HK1166425B - Programmable transmit continuous-time filter - Google Patents

Description

Programmable transmit continuous time filter

Cross Reference to Related Applications

The benefit of the filing date of U.S. provisional patent application No.61/145,638, filed on 19/1/2009, is claimed herein, and the specification thereof is incorporated herein by reference in its entirety.

Background

A transmit continuous-time filter (TX-CTF) is a frequency-selective circuit typically included in the transmitter portion of some types of cellular telephones (also referred to as handsets). The TX-CTF typically receives the output of a digital-to-analog converter (DAC) and attenuates DAC aliasing and noise. The output of the TX-CTF is typically provided to an active up-conversion mixer (upconversion mixer), which up-converts the signal from a baseband frequency to a desired Radio Frequency (RF) band for transmission.

Some tri-mode (tri-mode) cellular handsets support Wideband Code Division Multiple Access (WCDMA) modulation, Gaussian Minimum Shift Keying (GMSK) modulation used in the global system for mobile telecommunications (GSM) standard, and 8-phase shift keying (8PSK) modulation used in the enhanced data rates for global evolution (EDGE) standard, also known as the enhanced data rates for GSM evolution standard. Enabling all three of the above modes in the same handset imposes stringent performance requirements on the TX-CTF, including high current drive capability, high linearity, low input referred noise, and low bandpass ripple. Designing a TX-CTF that meets all these requirements can be problematic. Straightforward solutions to these problems that may be proposed, such as increasing the current, may cause other problems. For example, high TX-CTF current consumption may result in undesirably high current leakage on a cellular handset battery. It is desirable to minimize battery current leakage so that talk time and standby time (i.e., the amount of time the handset can be used before the battery needs to be recharged) can be maximized, and the battery size can be minimized.

A typical TX-CTF10 is shown in fig. 1. Since a typical cellular handset transmitter uses a form of quadrature modulation, the TX-CTF10 includes an in-phase (I) portion 12 and a quadrature (Q) portion 14. Since portions 12 and 14 are substantially identical, only portion 12 will be described in detail herein. The portion 12 includes two components 16 and 18. Component 16 may be, for example, a second order biquadratic (biquadratic) stage, and component 18 may be, for example, a first order real pole (real pole) stage. The component 16 includes a first amplifier 20 and a passive circuit that may include, for example, capacitors 22, 24, 26 and resistors 28, 30, 32, 34, 36, and 38. Passive circuits may be selected and connected to first amplifier 20 in an arrangement that defines desired filter parameters, such as filter poles and/or zeros representing second order biquad filter characteristics. Similarly, the component 18 includes a second amplifier 40 and a passive circuit that may include, for example, capacitors 42 and 44 and resistors 46, 48, 50 and 52. The passive circuit of the component 18 may be similarly selected and connected to the second amplifier 40 in an arrangement that defines desired filter parameters, such as filter poles and/or zeros representing a first order real pole filter characteristic.

In operation, a differential input signal Vl (whose negative side is denoted "V1 _ N" and whose positive side is denoted "V1 _ P" in fig. 1) is provided to the stage 16, which stage 16 outputs a signal V2 (whose negative side is denoted "V2 _ N" and whose positive side is denoted "V2 _ P"). The signal V2 is in turn provided to the stage 18, which stage 18 outputs a signal V3 (the negative side of which is denoted "V3 _ N" and the positive side is denoted "V3 _ P").

As in a typical cellular handset, the in-phase (I) and quadrature (Q) outputs of the TX-CTF10 are provided to active up-conversion mixers 54 and 56, respectively. Each of the up-conversion mixers 54 and 56 is typically of the Gilbert cell type, which presents a high impedance to the TX-CTF 10. The TX-CTF10 can easily drive a high-impedance load with a low current and maintain the required linearity.

It would be desirable to provide TX-CTFs for multi-mode cellular handsets that can meet the above performance standards, or similar performance standards, without consuming excessive current.

Disclosure of Invention

Embodiments of the invention relate to a programmable current transmit continuous time filter (TX-CTF) system in a Radio Frequency (RF) transmitter and a method of transmitter operation. The input of the TX-CTF may receive a baseband transmit signal and the output of the TX-CTF may be provided to an up-conversion mixer for conversion to RF for transmission. The TX-CTF includes amplifier circuitry and passive circuitry that together define filter parameters. The TX-CTF also includes a programmable current circuit that provides a programmable bias current to the amplifier circuit. The TX-CTF system also includes control logic that receives one or more transmitter control signals and, in response, generates signals that control the bias current provided to the TX-CTF. The transmitter control signal may include, for example, one or more of the following: a transmitter modulation mode signal, a transmitter frequency band signal, and a transmitter power signal.

Other systems, methods, features and advantages of the invention will be, or will become, apparent to one with skill in the art upon examination of the following figures and detailed description.

Drawings

The invention may be better understood with reference to the following drawings. The components within the figures are not necessarily to scale, emphasis instead being placed upon clearly illustrating the principles of the present invention. Moreover, in the figures, like reference numerals designate corresponding parts throughout the different views.

Fig. 1 is a block diagram illustrating a known or previous transmit continuous-time filter (TX-CTF) connected to an active up-conversion mixer.

Fig. 2 is a block diagram of an exemplary cellular handset including a transmitter portion having a TX-CTF system according to an exemplary embodiment of the present invention.

Fig. 3 is a block diagram of the example transmitter portion of fig. 2.

Fig. 4 is a block diagram of the exemplary TX-CTF system of fig. 3.

Fig. 5 is a block diagram of an exemplary second amplifier system of the TX-CTF system of fig. 4.

Fig. 6A is a flow diagram illustrating example decision logic for the second amplifier system of fig. 5.

Fig. 6B is a continuation of the flowchart of fig. 6A.

Fig. 7 is a block diagram of the bias control logic portion of the exemplary first stage bias generator circuit of the second amplifier system of fig. 5.

Fig. 8 is a block diagram of a PFET signal generator portion of an example first stage bias generator circuit of the second amplifier system of fig. 5.

Fig. 9 is a block diagram of the NFET signal generator portion of the exemplary first stage bias generator circuit of the second amplifier system of fig. 5.

Fig. 10 is a block diagram of a programmable current first stage of the second amplifier system of fig. 5.

Fig. 11 is a block diagram of a programmable current second stage of the second amplifier system of fig. 5.

FIG. 12 is a table illustrating an example relationship between a control signal and a resulting first stage bias current.

FIG. 13 is a table illustrating an example relationship between another control signal and a resulting second stage bias current.

Detailed Description

As shown in fig. 2-3, in the illustrated or exemplary embodiment of the present invention, a mobile wireless telecommunications device 58, such as a cellular telephone handset, includes a Radio Frequency (RF) subsystem 60, an antenna 62, a baseband subsystem 64, and user interface components 66. The RF subsystem 60 includes a transmitter section 68 and a receiver section 70. The output of transmitter section 68 and the input of receiver section 70 are coupled to antenna 62 via a front end module 72, which front end module 72 allows both the transmitted RF signal generated by transmitter section 68 and the received RF signal provided to receiver section 70 to pass through simultaneously. For certain elements of the transmitter portion 68 described below, however, the elements listed above may be of the type conventionally included in such mobile wireless telecommunications devices. These are referred to by the present invention as conventional elements, are well understood by those of ordinary skill in the art, and therefore are not described in further detail herein. However, unlike the conventional transmitter portion of such mobile wireless telecommunication devices, the transmitter portion 68 includes a transmit continuous time filter (TX-CTF) system 74 (fig. 3), which has the features described below.

The transmitter portion 68 receives as input a digital baseband signal from the baseband subsystem 64 (fig. 1) and outputs an RF signal to be transmitted. The transmitter portion 68 also includes a digital-to-analog converter 76, a dual-mode modulator and up-conversion mixer 78, and a power amplifier system 80. A digital-to-analog converter 76 converts the digital baseband signal to analog form and provides the resulting analog baseband signal to TX-CTF system 74. The output of the TX-CTF system 74 is provided to a dual mode modulator and up-conversion mixer 78. The output of the dual mode modulator and up-conversion mixer 78 is provided to a power amplifier system 80.

The baseband subsystem 64 may control various operational aspects of the mobile wireless telecommunications device 58 through an internal microprocessor system or similar logic (logic) (not separately shown). For example, the baseband subsystem 64 may generate one or more transmitter control signals on one or more connections 82 (e.g., a digital bus) that affect the operation of the transmitter portion 68. The transmitter control signal may include, for example, one or more of the following: a transmitter modulation mode signal, a transmitter frequency band signal, and a transmitter power signal.

In an example embodiment, the transmitter modulation mode signal may indicate that the modulator and the up-conversion mixer 78 are operating in a selected one of at least two modulation modes. As is well understood in the art, a multi-mode (e.g., dual-mode or tri-mode) cellular handset enables roaming between geographic areas where cellular telecommunication standards differ. In this example embodiment, the modulation modes may include WCDMA modulation associated with the WCDMA standard and GMSK modulation associated with some aspects of the GSM standard and the EDGE standard, although in other embodiments more than two modes may be present. As is well understood in the art, the EDGE standard uses GMSK modulation for the lower four of its nine modulation and coding schemes and higher order 8PSK modulation for the upper five of the nine modulation and coding schemes.

In response to a transmitter modulation mode signal representing a command or instruction issued by baseband subsystem 64 to operate in the WCDMA mode, transmitter section 68 modulates signals to be transmitted in accordance with the WCDMA standard, in a manner well understood in the art. In response to a transmitter modulation mode signal representing a command or instruction issued by the baseband subsystem 64 to operate in EDGE modulation mode, the transmitter portion 68 modulates the signal to be transmitted in accordance with the EDGE standard, i.e., GMSK or 8PSK modulation. In response to a transmitter modulation mode command issued by the baseband subsystem 64 to operate in GSM mode, the transmitter portion 68 modulates the signal to be transmitted in accordance with the GSM standard, i.e., GMSK modulation. Although in the exemplary embodiment the modes include any two or more of GSM, EDGE, and WCDMA, in other embodiments the mode selected in response to the transmitter modulation mode signal may include these or any other modulation modes known in the art.

The transmitter band signal may indicate that the modulator and up-conversion mixer 78 operate in a selected one of two or more (frequency) bands. In this example embodiment, there are a high band and a low band, although in other embodiments there may be more than two bands. As is well understood in the art, dual-band, tri-band, quad-band, etc. cellular handsets enable operation in geographic areas where cellular telecommunication standards specify different frequency bands. In response to a transmitter band signal representing a command issued by the baseband subsystem 64 to operate in a selected frequency band, the transmitter section 68 up-converts the signal to be transmitted to the selected frequency band.

The transmitter power signal may include one or more signals indicating the output power at which transmitter portion 68 is operating, indicating the output power at which transmitter portion 68 is indicated to operate, or in any other manner related to the power of the transmitted RF signal. For example, the baseband subsystem 64 may issue power control commands that instruct the power amplifier system 80 to set its gain to a selected value and thus amplify its input signal to a corresponding power level. The control circuit 84 in the power amplifier system 80 provides a closed loop feedback system that maintains the power amplifier 86 at a selected power level, or makes other adjustments in response to other conditions, as is also well understood in the art. There may be any number of selectable power levels, but here for illustrative purposes there may be two selectable power levels: a low power level and a high power level. It will be appreciated by those skilled in the art that the values of the low and high power levels may be in accordance with applicable standards (e.g., WCDMA, EDGE, GSM, etc.), but here for illustrative purposes it need only be understood that there are at least two different selectable power levels.

Another transmitter power signal that may be included in addition to or instead of the amplifier power control signal described above may indicate a measured or detected power level at which transmitter portion 68 is actually operating. A signal 88 indicative of such measured power level at which the transmitter portion 68 is operating is generated in the control circuit 84 as part of a closed loop feedback power control process.

Another transmitter power signal that may be included in addition to or instead of the above-described amplifier power control signal may indicate a "back-off" condition in which transmitter operation transitions from higher transmit power to lower transmit power. Although not shown for purposes of clarity, transmitter portion 68 may back off its transmit power by, for example, switching the attenuation circuit to the signal path. Such fallback mechanisms are conceived by the WCDMA standard. However, in embodiments of the present invention, the transmitted power control signal may indicate such a WCDMA fallback situation or any other similar type of fallback situation.

The TX-CTF 74 system receives one or more of the above-described transmitter control signals and, in response, adjusts the bias current provided to its amplifier circuitry, as described in further detail below.

As shown in FIG. 4, in the exemplary embodiment, TX-CTF system 74 includes an in-phase (I) portion 92 and a quadrature (Q) portion 94. Since the in-phase portion 92 and the quadrature 94 are substantially identical, only the in-phase portion 92 will be described in detail herein. The in-phase portion 92 includes first and second members 96 and 98. Component 96 may define, for example, a second order biquad filter, and component 98 may define, for example, a real pole (real pole) filter. The component 96 includes a first amplifier 100 and a passive circuit that may include, for example, capacitors 102, 104, 106 and resistors 108, 110, 112, 114, 116, and 118. In an arrangement defining desired filter parameters, such as filter poles and zeros representing second order biquad filter characteristics, a passive circuit may be selected and connected to the first amplifier 100. Similarly, the component 98 includes a second amplifier system 120 and a passive circuit that may include, for example, capacitors 122 and 124 and resistors 126, 128, 130, and 132. The passive circuit of the component 98 may be selected and connected to the second amplifier system 120 in an arrangement that defines desired filter parameters, such as filter poles and zeros representing a first order real pole filter characteristic. Although in the exemplary embodiment, component 96 defines a second order biquad filter and component 98 defines a first order real pole filter, in other embodiments, either component may comprise any other suitable type of continuous time filter.

In operation, a differential input signal Vl (whose negative side is denoted "V1 _ N" and positive pole is denoted "V1 _ P" in fig. 4) is provided to block 96, which block 96 outputs a signal V2 (whose negative pole is denoted "V2 _ N" and positive pole is denoted "V2 _ P"). The signal V2 is in turn provided to a block 98, which block 98 outputs a signal V3 (the cathode of which is denoted "V3 _ N" and the anode of which is denoted "V3 _ P").

The in-phase (I) and quadrature (Q) outputs of the TX-CTF system 74 are provided to a modulator and up-conversion mixer 78 (fig. 3). In an example embodiment, the modulator and up-conversion mixer 78 includes a passive, rather than an active, up-conversion mixer circuit. Passive mixers consume less current and can operate at lower supply voltages than active mixers. Thus, the use of a passive mixer is advantageous for reducing power consumption, and also for implementing the circuit at a lower supply voltage, which allows for a smaller handset battery. The passive up-conversion mixer circuit of the modulator and up-conversion mixer 78, similar to the active up-conversion mixer circuit, performs frequency conversion of the signal so that the signal is centered at the RF carrier frequency. However, in a passive up-conversion mixer circuit, frequency conversion, i.e., up-conversion, also results in a potentially disadvantageous reduction of the input impedance of the modulator and up-conversion mixer 78. Thus, in order for TX-CTF system 74 to drive modulator and up-conversion mixer 78 with a sufficient power level, TX-CTF system 74 is provided with a much lower output impedance than prior TX-CTF10 (FIG. 1). In the following manner, TX-CTF system 74 provides such a lower output impedance without sacrificing the linearity required for GMSK modulation and without consuming excessive current.

Note also that the use of a passive up-conversion mixer circuit results in much more noise being transferred from the TX-CTF system 74 to the RF output than if an active up-conversion mixer circuit were used. Such noise originating from the transmitter portion 68 (fig. 2) may undesirably couple into the receiver portion 70. A high level of transmitter noise may prevent proper transceiver operation and may exceed allowable thresholds established by WCDMA, GSM, EDGE, or other standards. However, in some examples of handset operation, such as operation in a WCDMA mode, the allowable threshold for noise established by the WCDMA standard depends on the transmit power. For example, a lower threshold of noise is allowed when the handset is transmitting at high power levels. Conversely, a higher threshold of noise is allowed when the handset is transmitting at a low power level. In addition, when the transmitter is operating in the WCDMA fallback situation described above, i.e. when the transmitter power is decreasing from a higher level to a lower level, the allowed noise threshold increases as the power decreases. An example of such an increase in the allowed noise threshold relative to the transmitter power is an increase of one decibel for each decibel of power decrease. The low noise in TX-CTF system 74 requires high current. Conversely, a higher current may be used to achieve a higher noise in TX-CTF system 74. In the manner described below, TX-CTF system 74 facilitates minimization of current consumption by providing a lower noise threshold in response to handset operating conditions, such as the low, high, and reverse transmitter power conditions described above.

The second amplifier system 120 (fig. 4) of the in-phase (I) section 92 is illustrated in further detail in fig. 5. Although the quadrature (Q) portion 94 includes another such second amplifier system, the other second amplifier system is the same as the second amplifier system 120 and, therefore, is not described herein.

As shown in fig. 5, the second amplifier system 120 includes a programmable current first stage 134, a programmable current second stage 136, and decision logic 138. In the illustrated embodiment, the decision logic 138 receives the transmitter control signal described above and, in response, controls or programs the bias currents provided to the amplifier circuits (described below) of the programmable current first stage 134 and the programmable current second stage 136. Decision logic 138 may comprise any suitable logic that enables the determination of the amount of bias current to be provided. For example, the decision logic 138 may comprise a microprocessor or digital signal processor (not shown) programmed according to the logic represented by the flow charts of fig. 6A-B. In an example embodiment, one output of the decision logic 138 representing the amount of bias current to be provided to the programmable current first stage 134 is represented by a 3-bit digital word or signal ISET including bits ISET0, ISET1 and ISET 2. In an example embodiment, another output of the decision logic 138, which is representative of the amount of bias current provided to the programmable current second stage 136, is represented by a 3-bit digital word or signal AB that includes bits AB0, AB1, and AB 2. (in an exemplary embodiment, the signal name "AB" is a reference to class AB of the amplifier circuit in the programmable second stage 136.) the inverter 139 provides the signal AB to the programmable current second stage 136 along with its complement.

As shown in fig. 6A-B, decision logic 138 may, for example, include several logic components related to the operation of programmable current first stage 134 and programmable current second stage 136 in response to handset operating conditions. It should be recalled from the above description with respect to fig. 4 that the programmable current first stage 134 and the programmable current second stage 136 are included in the second amplifier system 120 of the second component 98. 6A-B, the first logic 139 determines the amount of bias current provided to the programmable current first stage 134 in response to a combination of transmitter modulation mode and transmitter power; the second logic 141 determines the amount of bias current provided to the programmable current second stage 136 in response to the transmitter frequency band; the third logic 143 determines the amount of bias current provided to one or both of the programmable current first stage 134 and the programmable current second stage 136 in response to whether a combination of transmitter power and transmitter WCDMA power back-off conditions exist; and the fourth logic 145 determines the amount of bias current provided to the programmable current second stage 136 in response to the emitter modulation mode. Although these logic components are shown and described as sequential in the example embodiment for clarity, they may be integrated with one another in any other suitable manner. For example, in other embodiments, such logic components may work in parallel, or alternatively be combined in the form of a single logical operation, such as a formula evaluation in software or a network of logic in hardware.

The contributions to the total amount of bias current to be provided to programmable current first stage 134 and the total amount of bias current to be provided to programmable current second stage 136, represented by logic units 139, 141, 143, and 145, may be added together to determine a total. The logic represented by the flow diagrams of fig. 6A-B is intended to be exemplary only, and other suitable logic will be readily implemented by those skilled in the art to which the invention relates in view of the teachings herein. It should also be noted that the logic represented by the flow charts of fig. 6A-B is separated from other transceiver operations for clarity purposes. Those skilled in the art will appreciate that such logic is to be applied at the appropriate time, such as when a change in operating conditions occurs in the transceiver.

With respect to logic 139, if the transmitter modulation mode is WCDMA, as indicated by block 140, and if the transmitter power signal indicates that the transmitter power is low, as indicated by block 142, then decision logic 138 outputs an ISET signal to adjust the bias current provided to the programmable current first stage 134 to a lower or reduced level (relative to some predetermined range or scale within which the bias current level may be programmed), as indicated by block 144. For example, as described above, the bias current may be adjusted to a lower or reduced level by contributing a smaller number (selected from a predetermined range or scale of numbers) to the digital sum indicated by the ISET signal. If the transmitter modulation mode is WCDMA, as indicated by block 140, and if the transmitter power signal indicates that the transmitter power is high, as indicated by block 142, the decision logic 138 outputs an ISET signal to adjust the bias current provided to the programmable current first stage 134 to a higher or increased level, as indicated by block 146. For example, the bias current may be adjusted to a lower level by contributing a larger number to the sum of the numbers represented by the ISET signal.

With respect to the logic 141 portion, if the transmitter is operating in the low frequency band, as indicated by block 148, then the decision logic 138 outputs an AB signal to adjust the bias current provided to the programmable current second stage 136 to a lower or reduced level, as indicated by block 150. If the transmitter is not operating in the low frequency band (i.e., it is operating in the high frequency band), then decision logic 138 outputs an AB signal to adjust the bias current provided to the programmable current second stage 136 to a higher or increased level, as indicated by block 152.

With respect to logic 143, if the transmitter is operating in a power back-off condition, as indicated by block 154, then decision logic 138 outputs one or a combination of both of the ISET signal and the AB signal to adjust the bias current provided to one or both of the programmable current first stage 134 and the programmable current second stage 136, respectively, to a lower or reduced level, as indicated by block 156.

Additionally, in some embodiments, after the bias current has been adjusted in this manner, the decision logic 138 may also change the ISET signal to adjust the bias current provided to one or both of the programmable current first stage 134 and the programmable current second stage 136 to different bias current levels, i.e., different combinations of bias current levels provided to the programmable current first stage 134 and the programmable current second stage 136, while the transmitter is still in a power back-off condition. For example, the decision logic 138 may initially cause only the bias current provided to the programmable current first stage 134 to decrease and not cause the bias current provided to the programmable current second stage 136 to decrease. At some point in time thereafter (e.g., on the order of milliseconds), while the transmitter is still in a power-back condition, the decision logic 138 may cause both the bias current provided to the programmable current first stage 134 and the bias current provided to the programmable current second stage 136 to be further reduced or otherwise adjusted. Then, at a later point in time, but still while the transmitter is still in a power back-off condition, the decision logic 138 may also reduce or otherwise adjust the bias current provided only to the programmable current second stage 136, and not further reduce or otherwise adjust the bias current provided to the programmable current first stage 134. The foregoing adjustment sequences are intended as examples only, and other adjustment sequences will occur to those skilled in the art in view of the teachings herein.

With respect to logic block 145, if the transmitter is operating in a WCDMA modulation mode, as indicated by block 162, then decision logic 138 outputs an AB signal to adjust the bias current provided to programmable current second stage 136 to a lower or reduced level, as indicated by block 164. If the transmitter is not operating in the WCDMA modulation mode, the decision logic 138 outputs an AB signal to adjust the bias current provided to the programmable current second stage 136 to a higher or elevated level, as indicated by block 166.

In response to the ISET signal, bias control logic 168 (FIG. 5) in second amplifier system 120 generates a PFET (p-channel field effect transistor) digital control word or signal PCTRL comprising bits PCTRL2, PCTRL3, PCTRL4, PCTRL5, PCTRL6, and PCTRL7, and an NFET (n-channel field effect transistor) digital control word or signal NCTRL comprising bits NCTRL2, NCTRL3, NCTRL4, NCTRL5, NCTRL6, and NCTRL 7. Since the portion of the bias control logic 168 that generates the signal NCTRL is the same as the portion that generates the signal PCTRL, only the portion that generates the signal NCTRL is shown and described herein. It should be noted that the number of bits in the various signals described herein is merely exemplary, and in other embodiments, such signals may have any other suitable number of bits.

As shown in fig. 7, the portion of the bias control logic 168 that generates the signal NCTRL may include, for example, a network of combinational logic such as: inverters 170, 172, 174, 176, 178, 180, 182, 184, 186, 188, and 190; NOR gates 192, 194, and 196; a NAND gate 198; an OR gate 200; AND AND gates 202, 204, AND 206. The combinational logic shown in fig. 7 is merely an example, and those skilled in the art understand that the signal NCTRL may be generated in various other ways.

Referring again to fig. 5, in response to signal PCTRL and a fixed or constant PFET bias voltage VB P, the first stage PFET signal generator 208 generates a set of PFET control voltages VB P1, VB P2, VB P3, VB P4, VB P5, VB P6, and VB P7. Similarly, in response to signal NCTRL and a fixed or constant NFET bias voltage VB _ N, first stage NFET signal generator 210 generates a set of NFET control voltages VB _ N1, VB _ N2, VB _ N3, VB _ N4, VB _ N5, VB _ N6, and VB _ N7.

As further illustrated in fig. 8, the first stage PFET signal generator 208 includes six pairs of PFETs. In each pair, one PFET is controlled by one of the bits PCTRL2-PCTRL7 applied to the PFET gate, and the other PFET is controlled by the complement of the bit applied to the PFET gate. Similarly, as further illustrated in FIG. 9, the first stage NFET signal generator 210 comprises six pairs of NFETs. In each pair, one NFET is controlled by one of the bits NCTRL2-NCTRL7 applied to the gate of the NFET, and the other NFET is controlled by the complement of that bit applied to the gate of the NFET.

As shown in fig. 10, the programmable current first stage 134 receives a differential input signal Vl (i.e., signals V1_ N and V1_ P), control signals VB _ P and VB _ N, a fixed or constant supply voltage VDD, a fixed or constant common mode feedback voltage V _ CMFB, and a fixed or constant cascode (cascode) transistor bias voltage V _ CASC, and in response outputs a signal V2 (i.e., signals V2_ N and V2_ P). The programmable current first stage 134 includes a PFET branch 212 comprising 14 PFETs and an NFET branch 214 comprising 14 NFETs. The PFET branch 212 and the NFET branch 214 provide controllable or programmable bias currents to the amplifier transistor 215. As noted above, the programmable current first stage 134 shown in fig. 5 and 10 is included in the non-inverting (I) side of the system; the same programmable current first stage is included on the quadrature (Q) side of the system, but is not shown for purposes of clarity.

As shown in fig. 11, the programmable current second stage 136 receives the differential input signal V2 (i.e., signals V2_ N and V2_ P), the control signals AB0, AB1, and a2 and their complements, the fixed or constant second stage PFET bias voltage VAB _ P, the fixed or constant second stage NFET bias voltage VAB _ N, and the supply voltage VDD, and in response outputs the signal V3 (i.e., signals V3_ N and V3_ P). The programmable current second stage 136 includes three branches 216, 218, and 220. Branch 216 is still in the "on" state (i.e., signal AB0 remains high) and contributes the same bias current under all conditions of operation of the system, while branches 218 and 220 are used to contribute a controllable or programmable portion of the bias current. The programmable current second stage 136 shown in fig. 5 and 11 is included in the non-inverting (I) side of the system; the same programmable current second stage is included on the quadrature (Q) side of the system, but is not shown for purposes of clarity.

In operation, output signal V3 represents the result of filtering input signal V1 using TX-CTF system 74 (fig. 4), wherein the bias current provided to the amplification circuitry of second amplifier system 120 is controlled or programmed in response to one or more transmitter control signals.

The table in fig. 12 illustrates an example of the relationship between the ISET signal, the resulting bias current provided to each of the PFET branch 212 and NFET branch 214 (fig. 10) in the programmable current first stage 134, and the sum of the bias currents provided to these PFET and NFET branches in the combined in-phase and quadrature (Q) sides of the system.

The table in fig. 13 illustrates an example of the relationship between the AB signal, the resulting bias current provided to each of the branches 218 and 220 (fig. 10) in the programmable current second stage 136, and the sum of the bias currents provided to these branches in the combined in-phase and quadrature (Q) sides of the system.

In the manner described above with respect to the exemplary embodiments, the present invention adjusts the TX-CTF noise performance and linearity in response to transmitter operating conditions. In order to meet the performance requirements specified by the various standards involved by multimode transceivers (e.g., GMSK, EDGE, WCDMA, etc.), it is desirable to provide low noise and high linearity, but without the present invention, meeting all of the performance requirements of all of the various standards simultaneously under all of the various operating conditions can come at the expense of high current consumption. To meet this performance requirement with the lowest average power consumption, the present invention provides a low noise and high linearity that is no higher than required by the transmitter operating conditions.

As described above, changing the bias current supplied to the programmable current first stage 134 changes the noise in the amplification circuit in the programmable current first stage 134. The higher bias current provided to the programmable current first stage 134 results in low noise in the amplification circuit of the programmable current first stage 134. The lower bias current provided to the programmable current first stage 134 results in higher noise in the amplification circuit of the programmable current first stage 134. The noise performance of the amplification circuitry of programmable current first stage 134 is a major contributor to the overall noise of TX-CTF system 74 and ultimately transmitter portion 68 (fig. 2). For example, in the WCDMA mode, the noise requirements depend on the transmitter output power. At higher transmit powers, lower noise is required, and vice versa. Also, in the backward case, the noise requirements are relaxed. By programming programmable current first stage 134 in response to one or more of modulation mode, transmit power, and backoff conditions, TX-CTF system 74 provides low noise performance only when such operating conditions require it, thereby minimizing the average power consumption of TX-CTF system 74 as a whole and ultimately transmitter portion 68 as a whole.

Similarly, as described above, changing the bias current provided to the programmable second stage 136 changes the output current drive and linearity in the amplification circuit in the programmable current second stage 136. The higher bias current provided to the programmable current second stage 136 results in higher output current drive capability and higher linearity in the amplification circuit of the programmable current second stage 136. The lower bias current provided to the programmable current second stage 136 results in lower output current drive capability and lower linearity in the amplification circuit of the programmable current second stage 136. High current drive capability is required when high linearity performance of the TX-CTF system 74 is required, such as when the transmitter section 68 is in GMSK mode, or when the input impedance of the dual mode modulator and up-conversion mixer 78 is low, such as when the transmitter section 68 is operating in the high frequency band. Conversely, a lower current drive capability is sufficient when the lower linearity performance of the TX-CTF system 74 is sufficient, such as when the transmitter section 68 is in the WCDMA mode, or when the input impedance of the dual mode modulator and up-conversion mixer 78 is high, such as when the transmitter section 68 is operating in a low frequency band. By programming programmable current second stage 136 in response to one or both of transmitter mode and frequency band, TX-CTF system 74 provides high linearity performance only when needed for such operating conditions, thereby minimizing average power consumption by the entirety of TX-CTF system 74 and ultimately transmitter portion 68.

While various embodiments of the invention have been described, it will be apparent to those of ordinary skill in the art that many more embodiments and implementations are possible that are within the scope of the invention. For example, although examples of suitable emitter control signals and their use in determining the amount of bias current to be provided are described, others will be readily apparent to those skilled in the art in view of the teachings herein. Accordingly, it is not intended that the invention be limited, except as by the following claims.

Claims (19)

1. A system for a Radio Frequency (RF) transmitter, comprising:

a programmable current transmit continuous-time filter (TX-CTF) having an input configured to receive a baseband transmit signal prior to up-conversion to an RF signal at a transmitter, the programmable current TX-CTF further comprising a programmable current first CTF stage having an input configured to receive the baseband transmit signal, and a programmable current second CTF stage having an input configured to receive an output of the programmable current first CTF stage, the programmable current first CTF stage comprising: a first CTF stage amplifier circuit and a programmable first CTF stage current circuit configured to provide a programmable bias current to the first CTF stage amplifier circuit, the programmable bias current generated in response to first digital programming data, the programmable current second CTF stage comprising: a second CTF stage amplifier circuit and a programmable second CTF stage current circuit configured to provide a programmable bias current to the second CTF stage amplifier circuit, the programmable bias current generated in response to second digital programming data; and

control logic configured to receive one or more transmitter control signals and to generate the first digital programming data and the second digital programming data in response to the one or more transmitter control signals.

2. The system of claim 1, wherein the control logic is further configured to control at least one of linearity of the programmable currents TX-CTF and noise performance of the programmable currents TX-CTF by controlling at least one bias current in response to one or more transmitter control signals.

3. The system of claim 1, wherein the one or more transmitter control signals comprise at least one of a transmitter modulation mode, a transmitter frequency band, and a transmitter power.

4. The system of claim 1, further comprising a passive up-conversion mixer having an input coupled to an output of the programmable current TX-CTF.

5. The system of claim 1, wherein:

the one or more transmitter control signals comprise a transmitter power signal indicative of at least a low transmit power and a high transmit power;

the control logic is configured to generate first digital programming data to cause the programmable first CTF stage current circuit to generate a high bias current in response to a transmitter power signal indicating a high transmit power; and

the control logic is configured to generate first digital programming data to cause the programmable first CTF stage current circuit to generate a low bias current in response to a transmitter power signal indicating a low transmit power.

6. The system of claim 5, wherein:

the one or more transmitter control signals further include a transmitter modulation mode signal indicating at least a Wideband Code Division Multiple Access (WCDMA) mode and another mode;

the control logic is configured to generate first digital programming data to cause the programmable first CTF stage current circuit to generate a high bias current in response to a transmitter power signal indicating high transmit power when the transmitter modulation mode signal indicates the WCDMA mode; and

the control logic is configured to generate first digital programming data to cause the programmable first CTF stage current circuit to generate a low bias current in response to a transmitter power signal indicating low transmit power when the transmitter modulation mode signal indicates the WCDMA mode.

7. The system of claim 1, wherein:

the one or more transmitter control signals comprise a transmitter band signal indicating at least a low transmit frequency and a high transmit frequency;

the control logic is configured to generate second digital programming data to cause the programmable second CTF level current circuit to generate a low bias current in response to a transmitter band signal indicating a low transmit frequency; and

the control logic is configured to generate second digital programming data to cause the programmable second CTF stage current circuit to generate a high bias current in response to a transmitter band signal indicating a high transmit frequency.

8. The system of claim 1, wherein:

the one or more transmitter control signals comprise a transmitter modulation mode signal indicative of at least a Wideband Code Division Multiple Access (WCDMA) mode and a Gaussian Minimum Shift Keying (GMSK) mode;

the control logic is configured to generate second digital programming data to cause the programmable second CTF stage current circuit to generate a low bias current in response to a transmitter modulation mode signal indicating a WCDMA mode; and

the control logic is configured to generate second digital programming data to cause the programmable second CTF stage current circuit to generate a high bias current in response to a transmitter modulation mode signal indicating a GMSK mode.

9. The system of claim 1, wherein:

the one or more transmitter control signals comprise one or more transmitter power signals indicative of at least a low transmit power, a high transmit power, and a condition of backing off from a higher transmit power to a lower transmit power by attenuating the transmit signal; and

the control logic is configured to generate at least one of the first digital programming data and the second digital programming data to cause at least one of the programmable first CTF level current circuit and the programmable second CTF level current circuit to generate the low bias current in response to a transmitter power signal indicating a condition of backing off from a higher transmit power to a lower transmit power by attenuating the transmit signal.

10. The system of claim 9, wherein the condition of fallback from higher transmit power to lower transmit power comprises a WCDMA fallback condition.

11. A method for operating a Radio Frequency (RF) transmitter, comprising:

providing a baseband transmit signal to an input of a programmable current transmit continuous-time filter (TX-CTF), the TX-CTF including an amplifier circuit receiving a programmable bias current, the programmable current TX-CTF further including a programmable current first CTF stage having an input receiving the baseband transmit signal and a programmable current second CTF stage having an input receiving an output of the programmable current first CTF stage; and

controlling a bias current to the amplifier circuit in response to one or more transmitter control signals, including providing a high bias current to the programmable current first CTF stage in response to a transmitter power signal indicating a high transmit power; and providing a low bias current to the programmable current first CTF stage in response to a transmitter power signal indicating a low transmit power; and

the output of the programmable current TX-CTF is provided to an up-converter in the transmitter.

12. The method of claim 11, wherein providing the output of the programmable current TX-CTF to the upconverter comprises providing the output of the programmable TX-CTF to a passive mixer.

13. The method of claim 11, wherein the one or more transmitter control signals comprise at least one of a transmitter modulation mode, a transmitter frequency band, and a transmitter power.

14. The method of claim 11, wherein the programmable current TX-CTF comprises a programmable current first CTF stage having an input to receive a baseband transmit signal and a programmable current second CTF stage having an input to receive an output of the programmable current first CTF stage, the one or more transmitter control signals further comprising a transmitter modulation mode signal indicating at least a Wideband Code Division Multiple Access (WCDMA) mode and another mode, controlling the bias current in response to the one or more transmitter control signals comprising:

providing a high bias current to the programmable current first CTF stage in response to a transmitter power signal indicating a high transmit power and a transmitter modulation mode signal indicating a WCDMA mode; and

a low bias current is provided to the programmable current first CTF stage in response to a transmitter power signal indicating a low transmit power and a transmitter modulation mode signal indicating a WCDMA mode.

15. The method of claim 11, wherein the programmable current TX-CTF comprises a programmable current first CTF stage having an input to receive a baseband transmit signal and a programmable current second CTF stage having an input to receive an output of the programmable current first CTF stage, the one or more transmitter control signals comprise a transmitter band signal indicative of at least a low transmit frequency and a high transmit frequency, and controlling the bias current in response to the one or more transmitter control signals comprises:

a low bias current is provided to the programmable current second CTF stage in response to a transmitter band signal indicating a low transmit frequency.

A high bias current is provided to the programmable current second CTF stage in response to a transmitter band signal indicating a high transmit frequency.

16. The method of claim 11, wherein the programmable current TX-CTF comprises a programmable current first CTF stage having an input to receive a baseband transmit signal and a programmable current second CTF stage having an input to receive an output of the programmable current first CTF stage, the one or more transmitter control signals comprising one or more transmitter power signals indicating at least a low transmit power, a high transmit power, and a condition to fallback from a higher transmit power to a lower transmit power by attenuating the transmit signal, controlling the bias current in response to the one or more transmitter control signals comprising:

providing a low bias current to at least one of the programmable current first CTF stage and the programmable current second CTF stage in response to a transmitter power signal indicating a condition to back off from a higher transmit power to a lower transmit power by attenuating the transmit signal.

17. The method of claim 16, wherein the condition of fallback from higher transmit power to lower transmit power comprises a WCDMA fallback condition.

18. A system for a Radio Frequency (RF) transmitter, comprising:

control logic configured to receive one or more transmitter control signals and to provide first digital programming data and second digital programming data in response to the one or more transmitter control signals;

a programmable current first CTF stage having an input configured to receive a baseband transmit signal, the programmable current first CTF stage comprising: a first CTF stage amplifier circuit; and a programmable first CTF stage current circuit configured to provide a programmable bias current to the first CTF stage amplifier circuit, the programmable bias current generated in response to the first digital programming data; and

a programmable current second CTF stage having an input configured to receive an output of the programmable current first CTF stage, the programmable current second CTF stage comprising: a second CTF stage amplifier circuit; and a programmable second CTF stage current circuit configured to provide a programmable bias current to the second CTF stage amplifier circuit, the programmable bias current generated in response to the second digital programming data, the control logic configured to generate the first digital programming data and the second digital programming data in response to the one or more transmitter control signals; and

a passive up-conversion mixer having an input coupled to an output of the programmable current TX-CTF.

19. A wireless device, comprising:

a Radio Frequency (RF) receiver; and

an RF transmitter including a programmable current-transfer continuous-time filter (TX-CTF) having a baseband transmit signal configured for receiving prior to up-conversion to an RF signal in the transmitter, the programmable current TX-CTF further including a programmable current first CTF stage having an input configured for receiving the baseband transmit signal, and a programmable current second CTF stage having an input configured for receiving an output of the programmable current first CTF stage, the programmable current first CTF stage comprising: a first CTF stage amplifier circuit and a programmable first CTF stage current circuit configured to provide a programmable bias current to the first CTF stage amplifier circuit, the programmable bias current generated in response to first digital programming data, the programmable current second CTF stage comprising: a second CTF stage amplifier circuit and a programmable second CTF stage current circuit configured to provide a programmable bias current to the second CTF stage amplifier circuit, the programmable bias current generated in response to second digital programming data; and

control logic configured to receive one or more transmitter control signals and configured to generate the first digital programming data and the second digital programming data in response to the one or more transmitter control signals.