HK1082351B - Communication transmitter using offset phase-locked-loop - Google Patents

Description

Communication transmitter using offset phase locked loop

Technical Field

The present invention relates generally to signal processing systems, and more particularly to systems and methods for translating the frequency of a processed signal, for example, in a communication system.

Background

In order to transmit voice, data, and other types of baseband signals within a communication system, a variety of functions must be performed. These functions include filtering, amplification, and subsequent modulation of the signal onto a carrier frequency sufficient to meet system specifications. The type of modulation performed is used as the basis for classifying the transmitters. When modulation (or up-conversion) of a baseband signal is performed in two steps, the transmitter is said to have a double conversion architecture. And, when modulation is performed in one step, the transmitter is said to have a direct conversion architecture.

Fig. 1 shows a transmitter with a conventional double conversion architecture. The transmitter comprises a modulator which performs up-conversion of the baseband signal in two steps. In a first step, the in-phase (I) and quadrature (Q) components of the baseband signal are converted to an Intermediate Frequency (IF) according to a phase-shifted version of the local oscillator signal LO1 that is input into mixers 1 and 2. The intermediate frequency signals are then combined and translated to a carrier frequency in accordance with a second local oscillator signal LO2, which is input into the mixer 3. Finally, the resulting radio frequency signal is filtered, amplified, and transmitted through an antenna for demodulation in a subsequent receiver.

Fig. 2 shows a transmitter with a conventional direct conversion architecture. Unlike a transmitter of a dual conversion architecture, a direct conversion transmitter uses only one modulation step to generate a radio frequency transmit signal. Prior to modulation, the digital signals along the I and Q channels are converted to analog signals by DAC 4, filtered in a low pass filter 5, and amplified by a Variable Gain Amplifier (VGA) 6. The signals are then modulated in mixers 8 and 9 by mixing them with phase-shifted versions of the local oscillator signal LO, respectively. Since the local oscillator signal is set to the carrier frequency, the modulation is performed in a single step. To accomplish this, the modulated signals are combined, amplified, filtered, and transmitted through an antenna to a receiver. This particular modulation scheme is referred to as direct quadrature modulation.

Fig. 3 illustrates a transmitter having a third conventional architecture referred to as an offset-locked-loop (OPLL) architecture. Similar to dual conversion transmitters, translational-loop transmitters use two PLL circuits to generate the radio frequency signal. However, the translational-loop transmitter uses its PLL circuit in a very different manner.

Translational-loop transmitters differ from dual-conversion transmitters in the manner in which frequency conversion is performed. In the architecture of fig. 1, the intermediate frequency signal is mixed with a second local oscillator signal by mixer 3, translating the Intermediate Frequency (IF) signal to a carrier frequency. In a translational-loop transmitter, the mixer is replaced by a control unit 20 which performs the translation to the carrier frequency.

The control unit comprises a phase and frequency detector and a clock frequency (PFD)&CF) unit 22, a filter 24, a voltage controlled oscillator 26 in the forward signal path of the transmitter, and a mixer 27 and a filter 28 in the feedback path. The manner in which the control circuit performs frequency conversion will now be described. Firstly, the methodThe baseband signal containing the information to be transmitted is input to the first mixer 10. The baseband signal may be in the form of Gaussian Minimum Shift Keying (GMSK) data and the mixer may be a first mixer similar to a conventional dual-conversion transmitter. As shown, the mixer 10 uses a local oscillation signal F generated by a phase-locked loop circuit PLL2_LO2And converting the GMSK data from a baseband frequency to an intermediate frequency. Once the mixing is completed, the intermediate frequency signal is filtered by a band pass filter 15 to remove undesired or so-called image frequency components.

The control loop converts the intermediate frequency signal to a carrier frequency according to the following steps. First, a Voltage Controlled Oscillator (VCO) outputs a predetermined frequency F_VCOOf the signal of (1). The mixer 27 combines this signal with a second local oscillator signal F generated by a phase-locked loop PLL1_LO1And (4) mixing. The output of the mixer having two image frequencies F_VCO+F_LO1And F_VCO-F_LO1. The bandpass filter 28 removes the higher frequency signal and inputs the lower frequency signal to the PFD&And a CP unit.

PFD &The CP unit determines whether the frequency of the intermediate frequency signal output from the filter 15 matches the frequency of the signal output from the filter 28. If the signals do not match, PFD&The CP unit generates a difference signal indicating the amount of frequency mismatch present. This difference signal is filtered by filter 22 and input to the VCO to control F_VCOSuch that the frequency output from the filter 28 will match the intermediate frequency signal frequency. Since the VCO is tuned up to the output (F) of the filter 28_VCO-F_LO1) Matching F_LO2The intermediate frequency signal may be referred to as a reference signal.

Once frequency matching occurs between the two signals, the PFD & CP unit will compare the phase of the signal output from the filter 28 with the phase of the intermediate frequency signal. If there is a mismatch, the PFD & CP unit outputs a difference signal to adjust the output of the VCO until the phase of the signal output from the filter 28 matches the phase of the intermediate frequency signal. When the frequency and phase of the output of the filter 28 match the intermediate frequency signal, the frequency of the VCO will be set to the desired carrier frequency. The VCO then outputs the modulated baseband signal at the carrier frequency to the antenna for transmission.

Each of the above-described transmitters has advantages and disadvantages.

Dual-conversion transmitters are desirable because narrowband filtering and gain control can be efficiently implemented at the Intermediate Frequency (IF) stage. Also, by using two local oscillator frequencies to generate the transmit signal, the dual-conversion transmitter avoids a problem known as injection pulling, a phenomenon that often occurs in direct-conversion transmitters. Dual-conversion transmitters have also proven to be less problematic than other types of radio frequency transmitters.

Despite these advantages, dual-conversion transmitters also suffer from drawbacks that, in some instances, make them undesirable. Perhaps most notably, dual-conversion transmitters require more hardware than, for example, direct-conversion transmitters. Most of these hardware is in the form of filters and oscillator circuits for performing a first (or intermediate frequency) up-conversion of the baseband signal. Dual-conversion transmitters also use a separate phase-locked loop (PLL) circuit to generate the oscillating signal required for upconversion. While these drawbacks have proven significant in terms of cost and complexity, many Code Division Multiple Access (CDMA) and Time Division Multiple Access (TDMA) mobile telephone systems in use today use this type of transmitter.

Direct conversion transmitters provide advantages that dual conversion transmitters and translational-loop transmitters cannot achieve. For example, as discussed above, a direct-conversion transmitter uses less hardware than a dual-conversion transmitter because it uses only one local oscillation frequency to generate the transmit signal. Thus, only one PLL is required. The same advantages exist with respect to translational-loop transmitters that also use two PLL circuits to generate the radio frequency signal. Direct conversion transmitters also do not require the feedback loop found in translational-loop transmitters. Direct conversion transmitters therefore use less hardware and are therefore more suitable for use in cell phones and other highly integrated applications.

Despite these advantages, direct conversion transmitters also have a number of significant disadvantages. For example, direct conversion transmitters use duplex filters to meet specifications for noise reduction in the receive band of the communication system. These filters cause several dB of loss to occur in the transmitter, which must be compensated by additional power from the power amplifier. This so-called "back-off" power significantly shortens talk time. Thus, direct conversion transmitters are not the best choice for many mobile applications. For example, translational-loop filters (without the use of duplex filters) have become more commonly used in TDMA applications (e.g., GSM) than direct conversion architectures.

Translational-loop transmitters provide advantages not available with the first two types of transmitters. The PLL used in the feedback loop minimizes external filtering, for example, by acting like a tracking narrowband bandpass filter. This makes translational-loop transmitters desirable for use in GSM handsets to reduce cost and power consumption requirements.

The translational-loop transmitter also implements a low noise platform. This allows to replace the duplex filter used in the direct conversion architecture with a simple switch. As a result, the insertion loss associated with the duplex filter is eliminated, which allows the power amplifier in the transmitter to operate at low output power. Unlike many other transmitter architectures, class C power amplifiers can be used, providing good power boosting efficiency. This is particularly important in GSM systems where the modulation is a constant envelope signal.

An attendant benefit of a variable frequency loop system is that the VCO removes any residual Amplitude Modulation (AM) component that may be present. This allows the class C amplifier to be driven more strongly, thereby providing an additional measure of power added efficiency.

Translational-loop transmitters also have a number of disadvantages relative to all of their advantages, making them less than optimal in terms of performance when applied to mobile communication systems. Perhaps most notably, these transmitters must use multiple PLL circuits to generate the oscillating signals needed to convert the baseband signal to a carrier frequency. These additional oscillators increase the physical size and cost of the handset, as well as increase the power requirements. As a result, conventional translational-loop transmitters dissipate charge stored in the handset battery at a faster rate than desired.

Accordingly, there is a need for an improved system and method for modulating signals in a translational-loop transmitter, and more particularly, which generates modulated signals in a more economical and energy-efficient manner than conventional translational-loop transmitters, while having a more integrated architecture that occupies less space when incorporated into, for example, a mobile handset.

Disclosure of Invention

It is an object of the present invention to provide an improved system and method for modulating signals in a translational-loop transmitter.

It is another object of the present invention to achieve the above objects by generating a modulated signal in a manner that is more economical and energy efficient than conventional translational-loop transmitters.

It is a further object of this invention to achieve the above objects by using fewer oscillator circuits and/or less complex hardware than conventional translational-loop transmitters.

It is a further object of the present invention to provide a translational-loop transmitter which has a higher degree of integration than conventional transmitters of this type and therefore occupies less space when incorporated in, for example, a mobile handset.

It is a further object of the present invention to provide an improved method of generating an oscillating signal for frequency conversion in a translational-loop modulator.

These and other objects and advantages of the present invention are achieved by providing a system and method for generating a transmitter signal using at most one phase-locked loop circuit. According to one embodiment of the invention, the system comprises: the phase-locked loop circuit includes a phase-locked loop unit generating a reference oscillation signal, and a local oscillation signal generator generating a first oscillation signal and a second oscillation signal from the reference signal. The first and second oscillator signals are harmonically related with respect to a desired carrier frequency and their frequencies are selected to ensure that their sum equals the carrier frequency. To generate the transmitter signal, a first oscillator signal is mixed with a baseband signal to form an intermediate frequency signal, and a second oscillator signal is input to a frequency translation loop to be used as a basis for translating the intermediate frequency signal to a carrier frequency.

A second embodiment of the present invention comprises: a first oscillator for generating an oscillation signal; a mixer for mixing the oscillation signal with an input signal to generate an intermediate frequency signal; a frequency divider for dividing the frequency of the second oscillator to generate a feedback signal; and a comparator for comparing the feedback signal with the intermediate frequency signal to generate a difference signal, and outputting a control signal for setting the second oscillator to a desired carrier frequency according to the difference signal. The frequency divider and comparator may be included in a frequency conversion loop of a transmitter. In these cases, if the frequency of the first oscillator is (N/M) F_CThe frequency divider is arranged to multiply the frequency of the second oscillator by (N/M), where N and M are integers. The first oscillator may be a phase locked loop unit and the second oscillator may be a voltage controlled oscillator.

A third embodiment of the system of the present invention is similar to the second embodiment except that if the first oscillator is set to a frequency (N/M) F_CThe divider multiplies the output of the first oscillator by (1/M) and the frequency of the second oscillator by a fraction (1/N). Given these parameters, the translational loop of the transmitter outputs the modulated signal at the desired carrier frequency.

The fourth embodiment of the present invention generates an oscillation signal without using a phase-locked loop at all. This system comprises: a first oscillator for generating a crystal oscillator signal; a mixer for mixing an input signal with the crystal oscillator signal to generate an intermediate frequency signal; a frequency divider for dividing the frequency of the second oscillator to generate a feedback signal; and a comparator for comparing the feedback signal with the intermediate frequency signal to obtain a difference signal and outputting a control signal for setting the second oscillator to a desired carrier frequency according to the difference signal. The frequency divider divides the frequency of the second oscillator by a value such that the frequency of the feedback signal is equal to the frequency of the intermediate frequency signal. Also, the second oscillator may be a voltage controlled oscillator.

Various embodiments of the method of the present invention perform the functions of the systems described above. With such a system and method, the number of phase-locked loop circuits used in conventional translational-loop transmitters can be significantly reduced or eliminated altogether. This allows the size and power requirements of the mobile handset to be reduced, thereby improving miniaturization and providing longer battery life.

Drawings

The present invention will be described in detail with reference to the drawings, wherein like reference numerals denote like elements, and wherein

Fig. 1 is a schematic diagram illustrating a conventional dual-conversion transmitter.

Fig. 2 is a schematic diagram illustrating a conventional direct conversion transmitter.

Fig. 3 is a schematic diagram illustrating a conventional translational-loop (or offset-phase-locked-loop) transmitter.

Fig. 4 is a schematic diagram illustrating the modulation portion of a translational-loop transmitter using a single phase-locked loop for local oscillator generation in accordance with a first embodiment of the present invention.

Fig. 5 is a schematic diagram illustrating an exemplary configuration of a Local Oscillation (LO) signal generator shown in fig. 4.

Figure 6 is a flow chart illustrating the steps involved in one embodiment of the method of the present invention.

Fig. 7 is a schematic diagram illustrating a modulation portion of a translational-loop transmitter in accordance with a second embodiment of the present invention.

Fig. 8 is a schematic diagram illustrating a modulation portion of a translational-loop transmitter in accordance with a third embodiment of the present invention.

Fig. 9 is a schematic diagram illustrating a modulation portion of a translational-loop transmitter in accordance with a fourth embodiment of the present invention.

Detailed Description

The present invention is a system and method for modulating signals in a communication system. The invention is particularly applicable to modulating signals in a translational-loop (also referred to as an offset-phase-locked-loop) transmitter of a wireless communication system, however, it will be appreciated by those skilled in the art that the invention is not limited to this application. For example, the present invention may be used to modulate signals in a wired communication system using constant envelope modulation, or in any other system using modulated signals. The invention is also not limited to the generation of modulated signals but can be applied in any system where frequency conversion is required. For example, the present invention may be used to generate local oscillator signals used to demodulate various signals in a communication receiver, if desired. For purposes of illustration only, the present invention will be described below with respect to one application in a translational-loop transmitter.

Referring to fig. 4, a system for modulating various signals according to a first embodiment of the present invention uses a single oscillation element 40 in a translational-loop transmitter to generate a local oscillation signal. The oscillating unit comprises a Phase Locked Loop (PLL) unit 41 which is connected to a Local Oscillation (LO) signal generator 42 (the remainder of the transmitter is similar to that in fig. 3 and therefore the same reference numerals have been used where available).

In operation, the PLL unit provides a reference oscillation signal to the LO signal generator, and the LO signal generator generates two local oscillation signals from the reference signal. An exemplary configuration of the LO signal generator is shown in fig. 5. In this figure, the LO signal generator is shown as comprising a first frequency divider 51 and a second frequency divider 52. The first frequency divider generates a local oscillation signal F which is input to the mixer 10_LO2Such that the frequency of a gaussian filtered minimum shift keying (GMSK) data signal may be up-converted from a baseband frequency to an intermediate frequency. A quadrature signal generator is preferred because a single-sided up-conversion is required to obtain the intermediate frequency. The second frequency divider generates a local oscillation frequency F which is input to a mixer 27 in a feedback loop section of a second modulation section of the translational-loop transmitter_LO1. The oscillation frequency F_LO1For generating a control signal for adjusting a Voltage Controlled Oscillator (VCO)26 which will result in a conversion of the intermediate frequency signal output from the filter 15 to the desired carrier frequency.

The LO signal generator generates a local oscillation signal F according to a control signal from the ratio control unit 53_LO1And F_LO2. In operation, this control unit sets the value of each frequency dividing unit such that the frequency F_LO1And F_LO2Relative to the carrier frequency harmonic. Specifically, F is generated_LO1So that it equals (N)₁/M₁)F_CAnd produce F_LO2So that it equals (N)₂/M₂)F_CIn the formula, F_CIs the desired transmitter carrier frequency. To generate this type of signal, the ratio control unit controls the division factors of the units 51 and 52 such that they satisfy the following equation:

in the formula, M₁And N₁Is an integer (1)

In the formula, K is an integer (2)

Wherein S and R are integers (3)

Equations (1) and (4) clearly show that the local oscillation signal F_LO1And F_LO2Carrier frequencies (f) representing different fractions_C) And these scores must add up to 1. Equation (2) clearly shows that none of the fractions may be an integer multiple of 1 (e.g., none of the fractions may be 1/2 because when it is multiplied by the integer 2, the result is 1). This is preferred to ensure that no harmonically related local oscillator signals are used to reduce harmonic mixing and parasitic leakage.

Equation (3) makes the relationship between the oscillation signals more clear. For example, if S < R, the oscillation signal F_LO2Is a ratio of F_O1A larger fraction of carrier frequencies. In the following table, F is illustrated_LO1And F_LO2Some possibilities of non-harmonic correlation with respect to the carrier frequency of the transmitter.

F	F	Sum of
			(3/5)fc	(2/5)fc	fc
(4/7)fc	(3/7)fc	fc
			(5/9)fc	(4/9)fc	fc
(7/9)fc	(2/9)fc	fc

Given the above equation, there will appear wherein F_LO1＝3/5f_CAnd F_LO2＝2/5f_CIs described in (1). In this group of cases, a translational-loop transmitter for receiving an oscillating signal according to the invention may operate in the following manner. This will be explained with reference to fig. 6, which shows the steps comprised in the first embodiment of the method of the present invention.

In an initial step, the PLL 41 outputs a reference oscillation signal to the LO signal generator 42. A ratio control unit 53 in the LO signal generator inputs a division factor (according to the amplitude of the reference signal) so that the frequency dividing units 51 and 52 output the oscillation signal F_LO1And F_LO2The two signals are not harmonically related to the desired transmitter carrier frequency in a manner that satisfies equations (1) through (4) above (block 60). In this example, F_LO1＝3/5f_CAnd F is_LO2＝2/5f_C。

In the modulation step, the mixer 10 mixes the input baseband signal with the oscillation signal F output from the LO signal generator_LO2To generate a frequency of 2/5f_COf the intermediate frequency signal (block 61). This signal is then filtered by a band-pass filter 15 to remove unwanted (e.g. mirrors)Like frequency) frequency components.

In the frequency conversion step, the oscillation signal F is used_LO1The intermediate frequency is converted to a carrier frequency. In performing this conversion, the intermediate frequency signal is used as a reference frequency for controlling the output voltage of the voltage controlled oscillator 26. This is done according to the following steps. First, a Voltage Controlled Oscillator (VCO) outputs a preset frequency F_VCOMixer 27 mixes this signal with a local oscillator signal F output from the LO signal generator_LO1＝3/5f_C(block 62). The output of the mixer having two image frequencies F_VCO+F_LO1And F_VCO-F_LO1. The bandpass filter 28 removes the higher frequency signal while going to the PFD&CP unit 22 inputs the lower frequency signal (block 63).

PFD &The CP unit determines whether the frequency of the intermediate frequency signal output from filter 15 matches the frequency of the signal output from filter 28 (block 64). If the signals do not match, PFD&The CP unit generates a difference signal representing the amount of frequency mismatch. This difference signal is filtered by a filter 24 and input to the VCO to control the frequency F_VCOSo that the frequency output from the filter 28 matches the intermediate frequency signal frequency, i.e., so that F_VCO-F_LO1＝F_LO2(block 65).

Once there is frequency matching between the two signals, the PFD&The CP unit compares the phase of the signal output from the filter 28 with the phase of the intermediate frequency signal (block 66). If there is a mismatch, PFD&The CP unit outputs a difference signal for adjusting the output of the VCO until the phase of the signal output from the filter 28 matches the phase of the intermediate frequency signal (block 67). When both the frequency and phase of the output of the filter 28 match the same parameters of the intermediate frequency signal, the frequency of the VCO will be set to the desired carrier frequency f_C. This is clear from equation (4), which shows that the VCO output is equal to F_LO1+F_LO2＝(2/5+3/5)f_C＝f_COf (c) is detected. Therefore, the VCO outputs a modulated baseband signal of a carrier frequency to the antennaBefore transmission (block 68).

Referring to fig. 7, a system for modulating a signal according to a second embodiment of the present invention differs from the first embodiment in two respects. The first difference relates to the way the local oscillator signal is generated. Unlike the first embodiment, the second embodiment generates only one local oscillation signal in order to modulate the baseband signal to a desired carrier frequency. This oscillation signal is generated by a Phase Locked Loop (PLL) unit 75 which outputs an oscillation signal F to the mixer 10_LOTo generate an intermediate frequency signal which is then filtered by a band pass filter 15.

The second difference relates to the way in which the frequency is up-converted to the carrier frequency. Unlike the first embodiment, the frequency conversion is not performed based on the local oscillation signal. In contrast, the mixer 27 in fig. 4 is replaced by a frequency divider unit 78. The frequency divider is arranged to divide the VCO frequency F_VCOIs divided by a value such that the filter 28 outputs a signal equal to the frequency of the intermediate frequency signal output from the filter 15. Therefore, if the oscillation signal F_LOIs carrier frequency F_CBy a fraction N/M, the divider 78 is set to divide the voltage controlled oscillator output by the same value N/M.

In order to modulate a desired carrier frequency using the embodiment of fig. 7, the following additional equations must be satisfied:

wherein K is an integer, f_BRepresenting the original signal carrying the information from the baseband, while f_IF，INRepresenting the intermediate frequency signal, which is one of the inputs to the mixer in the offset PLL.

This condition must be met because the input signal is somewhat compressed (labeled compressed GMSK data in the figure). Since the frequency divider 78 in the feedback path compresses the GMSK modulated input signal, the input data from the baseband modem can be expected to have finer resolution by the factor shown in equation (5). If the feedback factor is not abnormally large, the frequency conversion can be performed without difficulty. The desired carrier signal generation can be obtained by the following calculation. The output frequency of the band-pass filter 28 becomes the output of the VCO divided by N/M, i.e., (N/M) F_VCOAnd the output of the band-pass filter 15 becomes (N/M) f_C+(N/M)f_B. Since the phase and frequency detector 22 attempts to match the phase and frequency of the two input signals, the outputs of the band pass filter 15 and the band pass filter 28 will be the same. This means that:

f_vco＝f_C+f_B (8)

as is clear from equation (8), by appropriately designing the frequency division factor, a modulated carrier signal can be obtained.

The requirement of equation (6) is similar to equation (2) for the first embodiment of the present invention. To avoid violating this condition and thus avoid possible harmonic damage, the numerator N of the frequency divider must not equal 1. Moreover, to satisfy equation (6), no harmonic component of the LO signal should fall within the desired carrier signal. Thus, the frequency divider 78 may be used for frequency generation as well as frequency division.

Referring to fig. 8, a system for modulating a signal according to a third embodiment of the present invention is similar to the second embodiment, except for two points. First, an operational frequency divider 85 is included between the Phase Locked Loop (PLL)75 and the mixer 10. This frequency divider is set to be the slave PLL 75 (F)_LO＝N/M F_C) The output frequency is divided by the fraction 1/N. Therefore, the oscillation signal output from the frequency divider 85 is equal to F_LO＝1/M F_C。

Second, in order to match the intermediate frequency signal input to the PFD & CP unit, an integer divider 88 with a division factor of 1/M is included in the feedback loop of the control unit 80. An advantage of this divider is that it can be designed as a simple integer-N divider instead of a more complex fractional divider. Nonetheless, the VCO frequency with large spectral leakage is not related to a carrier frequency harmonic, and therefore, this advantage of the present invention is maintained.

Referring to fig. 9, a system for modulating a signal according to a fourth embodiment of the present invention does not use a phase-locked loop circuit to modulate a baseband signal up to a desired carrier frequency. In the signal modulation, the oscillator 91 has a crystal reference frequency F_refIs provided to input a local oscillation signal to the mixer 10 so as to convert a baseband signal into an intermediate frequency signal. In this case, the effective compression ratio is increased, and thus a more accurate baseband signal is required in order to satisfy the required modulation accuracy.

To provide a more accurate baseband signal, the signal in digital form (GMSK data) may be converted to an analog signal using a sigma-delta digital-to-analog converter 92. This type of converter is preferred because it has a very high resolution and therefore can output a baseband signal with the accuracy required to achieve proper modulation with a crystal reference frequency. The analog signal may be filtered with an active low pass filter 93 to remove unwanted quantization noise before being input to the mixer.

The mixer 10 outputs an intermediate frequency signal of the reference frequency of a crystal oscillator. This frequency is depicted as 26MHz, however, one skilled in the art will appreciate that other crystal oscillator frequencies may be readily used. In the present invention, a PLL for local signal generation may not be required. This significantly reduces the amount of hardware required to implement the present system and the associated current consumption. Instead of a PLL, a crystal oscillation frequency is used to generate a local oscillation signal, which is advantageous due to its high stability and high Q factor,

after the intermediate frequency signal is generated, it is filtered by the band-pass filter 15 and then input to the control unit 90 which up-converts the signal to a carrier frequency. To perform this function, a frequency divider 98 is used in the feedback loop to reduce the frequency of the voltage controlled oscillator to a value equal to the frequency of the intermediate frequency signal. This is achieved by setting the factor N of the frequency divider such that F_VCOand/N is the value of the crystal oscillator frequency (in this example, 26 MHz).

In summary, the present invention represents a significant improvement over conventional translational-loop transmitters because it uses less phase-locked loop circuitry to generate the local oscillator signal required to modulate a baseband signal to a carrier frequency. As shown in fig. 3, a conventional transmitter of this type uses two PLL circuits to generate an oscillation signal required to convert a baseband signal to a carrier frequency. The first through third embodiments of the present invention use a single PLL to perform this function, and the fourth embodiment does not use a PLL to modulate the baseband signal. As a result, the present invention can reduce the physical size, cost, and power requirements of a mobile telephone handset, thereby improving miniaturization and providing longer battery life.

Other modifications and variations of the present invention will be apparent to those skilled in the art in light of the foregoing disclosure. It will thus be apparent that while only certain embodiments of the invention have been specifically described herein, various modifications may be made without departing from the spirit and scope of the invention.

Claims (7)

1. A method for generating an oscillating signal, comprising:

generating a first oscillation signal from a reference oscillation signal; and

generating a second oscillation signal from the reference oscillation signal;

wherein the first and second oscillator signals are non-harmonically related with respect to a desired carrier frequency, wherein the first oscillator signal is equal toAndthe second oscillating signal is equal toIn the formula, F_CIs the desired carrier frequency, and wherein:

in which i is equal to 1 or 2, K, S, R, M₁、N₁、M₂And N₂Are integers.

2. The method of claim 1, further comprising:

mixing the second oscillation signal with a baseband signal to generate an intermediate frequency signal; and

setting a frequency of a voltage controlled oscillator in a translational frequency loop according to a first oscillating signal, the frequency of the voltage controlled oscillator corresponding to the desired carrier frequency.

3. The method of claim 1, wherein the first and second oscillating signals are generated by a single phase-locked loop device.

4. A system for generating an oscillating signal, comprising:

a phase-locked loop unit that generates a reference oscillation signal;

a local oscillator signal generator for generating a first oscillator signal and a second oscillator signal from the reference oscillator signal, wherein the first oscillator signal and the second oscillator signal are non-harmonically related with respect to a desired carrier frequency, wherein the first oscillator signal is equal toAnd the second oscillating signal is equal toIn the formula, F_CIs the desired carrier frequency, and:

in which i is equal to 1 or 2, K, S, R, M₁、N₁、M₂And N₂Are integers.

5. The system of claim 4, further comprising:

a first mixer that mixes the second oscillation signal and the baseband signal to generate an intermediate frequency signal; and

a frequency translation loop receiving the output of the first mixer, the frequency translation loop including a voltage controlled oscillator having a frequency set according to a first oscillating signal, the frequency of the voltage controlled oscillator corresponding to the desired carrier frequency.

6. The system of claim 5, wherein the translational ring further comprises:

a second mixer that mixes an output of the voltage controlled oscillator and the first oscillation signal to generate a feedback signal;

a phase/frequency detector for comparing said feedback signal with an intermediate frequency signal to obtain a control signal for setting said voltage controlled oscillator to said desired carrier frequency.

7. The system of claim 4, wherein the local oscillator signal generator generates the first and second oscillator signals from a single reference oscillator signal, the single reference oscillator signal being output from a single phase-locked loop unit.