CN1652462B - Television tuner and method for processing a received radio frequency signal - Google Patents

Abstract

A television tuner comprising: a first mixer for mixing a received radio frequency signal with a first oscillation signal to generate an intermediate frequency signal; a second mixer for mixing the intermediate frequency signal with a second oscillation signal to generate an in-phase base frequency output signal; a third mixer for mixing the intermediate frequency signal with a third oscillating signal to generate a quadrature baseband output signal; and a phase locked loop coupled to the first and second mixers for generating the first and second oscillating signals according to a selected channel of the received RF signal.

Description

TV tuner and method for processing a received radio frequency signal

technical field

The present invention relates to a TV tuner, in particular to a TV tuner with a single phase-locked loop.

Background technique

In a TV system, the cost of the tuner (tuner) usually occupies a large proportion in the overall cost, and as the demand for integrating the functions of the TV into the personal computer system (or other electronic devices) gradually increases, The consideration of reducing the cost of the tuner becomes more and more important. In fact, the TV tuner can be manufactured on the circuit board first, and then installed in the personal computer system, so the personal computer can also have the function of the TV. Such a tuner can convert an RF TV signal into a base frequency (or low frequency) video signal, and then transmit the base frequency (or low frequency) video signal to other components in the personal computer for subsequent video processing.

FIG. 1 is a schematic diagram of a conventional TV tuner 100 (US Patent No. 5,737,035). The tuner 100 in FIG. 1 includes an on-chip circuit 102 and an off-chip bandpass filter 104 . Chip circuit 102 includes a low noise amplifier (LNA) 106, a first mixer 108, a second mixer 110, a second IF amplifier 112, a plurality of first voltage-controlled oscillators 114, a first PLL 116 , a second VCO 118 , and a second PLL 120 .

Due to the use of an off-chip band-pass filter 104, a special-purpose image-rejection mixer (as the second mixer 110), and a plurality of phase-locked loops to control the frequency of each oscillation signal, the above-mentioned known technology Doing so will increase the overall cost and system complexity of the TV tuner 100 .

Contents of the invention

It is therefore an object of the present invention to provide a television tuner having a single phase locked loop.

The invention discloses a TV tuner, comprising: a phase-locked loop, including a first voltage-controlled oscillator used to generate a first oscillating signal, and a second voltage-controlled oscillator used to generate a second oscillating signal device; a first mixer, coupled with the phase-locked loop, used to mix a selected radio frequency signal with the first oscillating signal to generate an intermediate frequency signal; a second mixer, and the lock The phase loop is coupled to mix the intermediate frequency signal with the second oscillating signal to generate an output signal.

As for a method for processing a received radio frequency signal disclosed in the present invention, it includes: using a single first voltage-controlled oscillator in a phase-locked loop to generate a first oscillating signal according to a selected radio frequency signal, Using a single second voltage-controlled oscillator in the phase-locked loop to generate a second oscillating signal; mixing the selected radio frequency signal with the first oscillating signal to generate an intermediate frequency signal; and combining the intermediate frequency signal with the first oscillating signal The two oscillating signals are mixed to generate an output signal.

Description of drawings

FIG. 1 is a schematic diagram of a highly integrated TV tuner in the prior art.

FIG. 2 is a schematic diagram of an embodiment of the tuner of the present invention.

Fig. 3 is a schematic diagram of another embodiment of the tuner of the present invention.

FIG. 4 is a flowchart of a method for processing a received radio frequency signal according to the present invention.

Description of main component symbols

100, 200, 300 tuner

102 Chip Circuit

104 Bandpass filter

106, 202 Low noise amplifier

108, 110, 204, 230 mixers

112 Intermediate frequency amplifier

114, 118, 224, 226 Voltage Controlled Oscillator

116, 120, 218 phase-locked loop

206, 212 mixer

208, 214, 232 low pass filter

210, 216 gain amplifier

220 Phase Frequency Detector

222 loop filter

228, 304 90 degree phase delay unit

234 Frequency divider (divider)

302, 306, 310 Harmonic mixer

308 45 degree phase delay unit

Detailed ways

Please refer to FIG. 2 , which is a schematic diagram of an embodiment of the TV tuner of the present invention. The television tuner 200 among the present embodiment comprises: a variable gain low-noise amplifier (LNA) 202, a first mixer 204, in-phase mixer (in-phase mixer) 206, in-phase low-pass filter device 208, an in-phase programmable gain amplifier (PGA) 210, a quadrature mixer 212, a quadrature low-pass filter 214, a quadrature programmable gain amplifier 216, and a single phase-locked loop (PLL) 218. Phase locked loop 218 includes a phase frequency detector (PFD) 220, a loop filter 222, a first voltage controlled oscillator 224, a second voltage controlled oscillator 226, a 90 degree phase delay unit 228, a fourth Mixer 230, a low-pass filter 232, and a feedback divider 234 for dividing by M.

The variable gain low noise amplifier 202 can amplify a received radio frequency signal RF_in, and the first mixer 204 mixes the amplified radio frequency signal with a first oscillation signal LO1 to generate an intermediate frequency signal IF (in terms of frequency) , IF=LO1-RF). The in-phase mixer 206 mixes the IF signal with a second oscillating signal LO2 to generate an in-phase output signal 207 . Next, the non-inverting low-pass filter 208 is responsible for filtering the non-inverting output signal 207 to suppress the interference noise outside the channel, and then the non-inverting programmable gain amplifier 210 amplifies the signal output by the non-inverting low-pass filter 208 to generate a non-inverting base frequency signal I. Similarly, the quadrature mixer 212 mixes the IF signal with a signal LO2_90° (the result of a 90-degree phase delay of the second oscillator signal LO2 ) to generate a quadrature output signal 213 . Next, the quadrature output signal 213 is filtered by the quadrature low-pass filter 214, and then the quadrature programmable gain amplifier 216 amplifies the output signal of the quadrature low-pass filter 214 to generate a quadrature baseband signal Q.

In the embodiment of FIG. 2 , the phase-locked loop 218 is used to generate the first oscillating signal LO1 , the second oscillating signal LO2 , and the signal LO2_90°. The phase frequency detector 220 compares the phases of a reference signal F _REF and a feedback signal _FFB to generate a corresponding error signal 221 . The pulse width of the error signal 221 can be used to indicate the magnitude of the phase difference between the reference signal F _REF and the feedback signal _FFB . According to the speed relationship between the reference signal F _REF and the feedback signal F _FB represented by the error signal 221 , the capacitor in the loop filter 222 will be charged or discharged. In essence, the loop filter 222 works like an integrator to accumulate a net charge corresponding to the error signal 221 . The loop filter voltage V _TUNE generated by the loop filter is used for the first VCO 224 and the second VCO 226 . The first voltage-controlled oscillator 224 and the second voltage-controlled oscillator 226 can generate first and second oscillation signals LO1 and LO2 respectively. In order to simultaneously generate the in-phase and quadrature output signals, the 90-degree phase delay unit 228 can delay the phase of the signal LO2 to generate the signal LO2_90°. It should be noted here that, in practice, in addition to the method shown in FIG. 2 , the 90-degree phase delay unit can also be disposed outside the PLL circuit 228 .

Equation 1 below is used to show the relationship between the two oscillating signals LO1, LO2 and the selected channel in the RF signal. In Equation 1, RF represents the frequency of the selected channel in the received signal, LO1 is the frequency of the first oscillating signal, and LO2 is the frequency of the second oscillating signal.

RF = LO1 - LO2 (Equation 1)

The first voltage-controlled oscillator 224 and the second voltage-controlled oscillator 226 will have opposite reactions to the change of the loop filter voltage V _TUNE . For example, if the loop filter voltage V _TUNE becomes larger, the first oscillation The frequency of the signal LO1 will increase, and the frequency of the second oscillating signal LO2 will decrease. The following Equation 2 and Equation 3 respectively show the frequency variation ΔLO1 of the first oscillating signal LO1 and the frequency variation ΔLO2 of the second oscillating signal LO2 relative to the voltage variation of the loop filter voltage ΔV _TUNE and a VCO gain factor K. relation.

ΔLO1≈|K|*ΔV _TUNE (Equation 2)

ΔLO2≈(-|K|)*ΔV _TUNE (Equation 3)

Please note that the first voltage-controlled oscillator 224 and the second voltage-controlled oscillator 226 do not necessarily have the same VCO gain factor K, and the same symbol K is used in the above two equations mainly to indicate that the first voltage-controlled oscillator The oscillator 224 and the second VCO 226 respond in opposite directions to changes in the loop filter voltage V _TUNE . However, in other embodiments, the first VCO 224 may also have a first gain factor K ₁ , and the second VCO 226 may have a second gain factor K ₂ .

The fourth mixer 230 can mix the first and second oscillating signals LO1 , LO2 to generate a signal 231 . Signal 231 has a higher frequency component at frequency (LO1+LO2) and a lower frequency component at frequency (LO1-LO2). The low-pass filter 232 is responsible for filtering out the aforementioned frequency components at the frequency (LO1+LO2). As for a feedback frequency divider 234, the frequency component at the frequency (LO1-LO2) will be divided according to the selected channel in the received radio frequency signal RF_in. The frequency components of are divided by M. In this way, the feedback signal F _FB required in the operation of the closed-loop phase-locked loop can be generated. Equation 4 shows that the frequency of the selected channel in the received RF signal RF_in will be equal to the divisor M multiplied by the reference signal F _REF .

Frequency of selected channel = F _REF * M (Equation 4)

Next, the PFD 220 compares the phases of the signal F _REF and the feedback signal F _FB , and the loop filter voltage V _TUNE generated by the loop filter 222 can be used to control the first and second VCOs 224 , 226 . Since the phase-locked loop 218 has a closed-loop structure, when reaching a stable state, the first voltage-controlled oscillator 224 and the second voltage-controlled oscillator 226 will generate appropriate first oscillation signal LO1 and second oscillation signal LO2, and (LO1-LO2) will be M times the reference signal F _REF (this corresponds to the selected channel in the signal RF_in). Then, the first mixer 204, the second mixer 206 and the third mixer 212 can down-convert the selected channel in RF_in into the in-phase baseband signal I and the quadrature baseband signal Q.

Please refer to FIG. 3 , which is a schematic diagram of another embodiment of the tuner of the present invention. The TV tuner 300 generally includes components similar to the TV tuner 200, the difference is that the first mixer 204, the second mixer 206 and the third mixer 212 in FIG. It is changed to a first harmonic mixer (harmonic mixer) 302 , a second harmonic mixer 306 and a third harmonic mixer 310 . In addition, the TV tuner 300 further includes a second 90-degree phase delay unit 304 and a 45-degree phase delay unit 308 . The second 90-degree phase delay unit 304 can generate a 90-degree phase-delayed signal of the first oscillating signal LO1, and both the first oscillating signal LO1 and its 90-degree phase-delayed signal are coupled to the first harmonic mixer device 302. In addition, in the embodiment of FIG. 3 , both the second oscillation signal LO2 and its signal LO2_90° after a 90-degree phase delay are coupled to the second harmonic mixer 306. The 45-degree phase delay unit 308 generates the second The oscillating signal LO2 is coupled to the third harmonic mixer 310 after phase delays of 45 degrees and 135 degrees.

In practice, the first, second, and third harmonic mixers 302 , 306 , and 310 can all be implemented using passive harmonic mixers. For the operation, implementation, and features of the harmonic mixer, please refer to the US patent application No. 10/604018 "Passive Harmonic Mixer (Passive Harmonic Mixer)" filed in June 2003 . Due to the use of the harmonic mixers 302 , 306 and 310 , the first oscillating signal LO1 and the second oscillating signal LO2 provided by the phase-locked loop 218 only need to provide half the frequency in normal operation. This feature can reduce the design complexity of the PLL 218 . As for the operation mode and characteristics of the TV tuner with harmonic structure, please refer to the patent application "TV Tuner and Processing Based on Harmonic Mixer" filed in December 2003, U.S. No. 10/707319 Method of receiving radio frequency signals (HARMONIC MIXER BASED TELEVISION TUNER AND METHOD OF PROCESSING A RECEIVED RF SIGNAL)".

Please refer to FIG. 4 at last. FIG. 4 is a flowchart of a method for processing a received radio frequency signal according to the present invention. The steps in FIG. 4 will be described in detail below:

Step 400: Using a single PLL to generate a first and a second oscillating signal, wherein the frequency of the first oscillating signal minus the frequency of the second oscillating signal is equal to the frequency of a selected channel of the received RF signal. Go to step 402.

Step 402: Mix the received RF signal with the first oscillating signal LO1 to generate an intermediate frequency signal IF. Go to step 404.

Step 404: Mix the intermediate frequency signal IF and the second oscillating signal LO2 to generate an in-phase base frequency signal, and mix the intermediate frequency signal IF and the phase-delayed second oscillating signal LO2 to generate a quadrature base frequency signal .

According to the above-mentioned embodiment of the present invention, since the second mixer 206, 306 and the third mixer 212, 310 can directly convert the first intermediate frequency signal IF to the fundamental frequency, there is no need to use a bandpass filter to convert the image Signal removed. In addition, the second mixer 206, 306 and the third mixer 212, 310 can be general mixers. Moreover, in the tuner of the present invention, a phase-locked loop 218 is used to generate the oscillating signals LO1, LO2, which can reduce the number of components used by the tuner.

A preferred embodiment, because the interfering signal outside the frequency channel is just suppressed until low-pass filter 208,214, so front element (low noise amplifier 202, first mixer 204, quadrature mixer 212 and in-phase mixing The frequency converter 206) has better linearity and can reduce the influence of interference signals.

The above descriptions are only preferred embodiments of the present invention, and all equivalent changes and modifications made according to the claims of the present invention shall fall within the scope of the present invention.

Claims (10)

1. tuner includes:

One phase-locked loop includes one second voltage controlled oscillator that is used for producing one first voltage controlled oscillator of first oscillator signal and is used for producing second oscillator signal;

One first frequency mixer couples mutually with this phase-locked loop, is used for a selected radiofrequency signal and this first oscillator signal mixing to produce an intermediate-freuqncy signal;

One second frequency mixer couples mutually with this phase-locked loop, is used for this intermediate-freuqncy signal and this second oscillator signal mixing to produce an output signal.

2. tuner as claimed in claim 1, wherein the difference on the frequency of this first oscillator signal and this second oscillator signal equals the frequency of this selected radiofrequency signal.

3. tuner as claimed in claim 1, wherein this first voltage controlled oscillator is opposite for the reaction that variation produced of a control signal with this second voltage controlled oscillator.

4. tuner as claimed in claim 1, wherein this phase-locked loop also comprises:

One phase-frequency detector is used for comparison one reference signal and a feedback signal to produce an error signal;

One loop filter is coupled to this phase-frequency detector, is used for according to this error signal to produce a control signal;

One the 4th frequency mixer, with this first and this second voltage controlled oscillator couple mutually, be used for this first oscillator signal and this second oscillator signal mixing; And

One low pass filter is coupled to the 4th frequency mixer, is used for signal filtering that the 4th frequency mixer is exported.

5. method of handling a received RF signal, this method includes:

According to a selected radiofrequency signal, use a phase-locked loop to produce one first oscillator signal and one second oscillator signal;

Should select radiofrequency signal and this first oscillator signal mixing to produce an intermediate-freuqncy signal; And

With this intermediate-freuqncy signal and this second oscillator signal mixing to produce an output signal.

6. method as claimed in claim 5, wherein the difference on the frequency of this first oscillator signal and this second oscillator signal equals the frequency of this selected radiofrequency signal.

7. method as claimed in claim 5, wherein produce this first and the step of this second oscillator signal also comprise:

Relatively a reference signal and a feedback signal are to produce an error signal;

Produce a control signal according to this error signal;

Produce this first oscillator signal and this second oscillator signal according to this control signal;

With this first oscillator signal and this second oscillator signal mixing; And

The result who draws according to mixing produces this feedback signal.

8. method as claimed in claim 5, wherein this output signal also includes a homophase fundamental frequency signal and a quadrature baseband signal.

9. method as claimed in claim 5, wherein this first oscillator signal is opposite for the reaction that variation produced of this control signal with this second oscillator signal.

10. method as claimed in claim 5, wherein this first oscillator signal is opposite for the reaction that variation produced of a control signal with this second oscillator signal.

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