JP5444084B2 - Semiconductor receiver and automatic gain control method - Google Patents

Description

  The present invention relates to a receiver, and more particularly to a receiver suitable for being mounted on a semiconductor device and an automatic gain control method.

  The receiver has a function of converting the frequency of the received signal into an intermediate frequency (abbreviated as “Intermediate Frequency”, “IF”). A mixer circuit is used for frequency conversion. The difference between the frequency of the local oscillator (Local Oscillator, abbreviated as “LO”) signal (LO signal) and the received signal input to the mixer circuit is the frequency of the output signal (IF signal) of the mixer circuit. Assuming that the frequency of the IF signal is constant, the frequency of the received signal that can be received is changed by changing the frequency of the LO signal, and the frequency of the signal that is desired to be received can be controlled by the frequency of the LO signal. In general, a signal received by a receiver includes a signal having a frequency (desired wave) to be received and a signal having an unnecessary frequency (interference wave), and only the desired wave is output as an IF signal. Requires the following two functions.

(A) The LO signal frequency is adjusted so that the difference between the desired wave frequency and the LO signal frequency becomes the IF signal frequency.

(B) Since a desired wave and an interference wave appear in the mixer output signal, a filter circuit is provided after that to suppress the interference wave and extract the desired wave.

  The performance of the receiver regarding interference wave suppression is represented by an interference wave suppression ratio. It can be said that the higher the value of the interference wave suppression ratio, the better the receiver. Generally, when the frequency difference between the desired wave and the interference wave becomes small, the interference wave suppression ratio of the receiver deteriorates. For this reason, in the communication system, the interference wave suppression ratio is set to a relatively small value when the frequency difference is small, and is set to a large value when the frequency difference is large. As an example, FIG. 2 shows interference wave suppression ratio standards in various TV broadcasts. The horizontal axis is the channel difference between the desired wave and the interference wave, and the vertical axis is the interference wave suppression ratio standard (dB display). A broken line is DVB-T (Digital Video Broadcasting Terrestrial: terrestrial digital television broadcasting standard (according to NorDig standard), and a solid line is ATSC (Advanced Television System Committee).

  FIG. 3 is a diagram illustrating a circuit configuration of a related art receiver. A radio frequency variable gain amplifier (hereinafter referred to as “RFVGA”) 3 has a function that allows a gain to be varied by a control voltage. When the control voltage is high, the gain is large, and when the control voltage is low, the gain is small.

  The power detector (Power Detector, abbreviated as “DET”) 8 outputs a voltage corresponding to the power of the input signal.

  A differential amplifier (Differential Amplifier, abbreviated as “DIFFAMP”) 10 amplifies and outputs a difference voltage between the output voltage of the power detector 8 and a reference voltage (referred to as Reference Voltage, “Vref”) 9. . The output voltage of the differential amplifier 10 is applied as a control voltage for the high-frequency variable gain amplifier 3.

  Frequency converter (MIXER) 4. The frequency of the output signal of the high frequency variable gain amplifier 3 is converted to a difference frequency from the LO frequency. The converted signal is called an intermediate frequency (IF) signal.

  The output of the local oscillator (abbreviated as “LO”) 5 is input to the frequency converter 4 and used during frequency conversion. This LO signal frequency is changed according to the signal frequency to be received.

  The intermediate frequency low-pass filter (Intermediate Frequency Low Pass Filter, abbreviated as “IFLPF”) 6 is a filter that passes a signal having a frequency lower than a predetermined frequency (cut-off frequency) and blocks signals higher than that. In the case of a semiconductor receiver that is a receiver mounted on a semiconductor device, the semiconductor receiver includes an active filter using an active element.

  The automatic gain control loop 7 is a negative feedback loop for controlling the gain of the high-frequency variable gain amplifier 3, and includes the high-frequency variable gain amplifier 3, a power detector 8, a reference voltage (Vref) 9, and a differential amplifier 10. Yes.

  The input signal (RF signal) is amplified by the high frequency variable gain amplifier 3 and then detected by the power detector 8. The differential amplifier 10 amplifies and outputs a difference voltage between the output voltage of the power detector 8 and the reference voltage (Vref) 9. The output voltage of the differential amplifier 10 becomes the control voltage of the high frequency variable gain amplifier 3, and the high frequency variable gain amplifier 3 changes the gain according to the input control voltage.

  Here, assuming that the output power of the high-frequency variable gain amplifier 3 is high, when the output voltage of the power detector 8 is high and exceeds the reference voltage (Vref) 9, (Vref−output voltage of the power detector 8). The sign of becomes negative, and the output voltage of the differential amplifier 10 decreases. As a result, the gain of the high-frequency variable gain amplifier 3 decreases, and the output power of the high-frequency variable gain amplifier 3 decreases. When the output power of the high-frequency variable gain amplifier 3 decreases, the reverse operation is performed, and the output power increases.

  Thus, by applying negative feedback to the high-frequency variable gain amplifier 3 by the differential amplifier 10, the output voltage of the power detector 8 and the reference voltage (Vref) 9 are finally equalized, and the loop is Converge. Therefore, the output power of the high-frequency variable gain amplifier 3 can be controlled by changing the voltage value of the reference voltage (Vref) 9.

  An input signal (received signal) from the input 1 is amplified by the high frequency variable gain amplifier 3. The gain of the high-frequency variable gain amplifier 3 is variably controlled by a control voltage. The signal power amplified by the high frequency variable gain amplifier 3 is detected by the power detector 8 and fed back as a control voltage of the high frequency variable gain amplifier 3 through the differential amplifier 10. The differential amplifier 10 amplifies and outputs the difference between the reference voltage (Vref) 9 and the output voltage of the power detector 8. When the output voltage of the power detector 8 is higher than the reference voltage (Vref) 9, the control voltage supplied to the high frequency variable gain amplifier 3 is lowered. This series of loops is called an automatic gain control (AGC) loop, and a negative feedback loop is formed, so that the output power of the high-frequency variable gain amplifier 3 operates to be constant regardless of the received signal power.

  The output signal of the high-frequency variable gain amplifier 3 is input to the frequency converter 4 and frequency-converted to a difference frequency from the LO signal. Thereafter, unnecessary interference waves are suppressed by the intermediate frequency low-pass filter, and only desired waves to be received are output.

JP 2003-218711 A

  The problems of the related technology are described below.

  In the related technology described with reference to FIG. 3, the anti-input characteristic of the active filter constituting the intermediate frequency low-pass filter 6 has an undesirable frequency characteristic, so that a sufficiently high interference wave suppression ratio cannot be obtained. There is.

  Hereinafter, the cause of this problem will be described.

<About the performance of the active filter>
In general, when a filter is built in a semiconductor receiver, the active filter is configured by combining resistors, capacitors and an amplifier (operational amplifier). Since an active element is used for the amplifier, it functions as a filter only in a power range where the active element is not saturated. The higher the input power that does not saturate, the higher the S / N ratio (signal-to-noise ratio) at the output. This characteristic is called “input resistance characteristic” and is one of the performance indexes of the filter.

  Another important performance index of the filter is attenuation characteristics. The attenuation characteristic means an attenuation amount at a certain frequency, and the higher the attenuation amount, the higher the performance of the filter.

  In order to make the attenuation characteristic of the active filter steep, it is necessary to increase the order of the filter circuit. That is, the filter needs to have a multistage configuration (increase the number of stages) of resistors, capacitors, and amplifiers. In this case, the internal node of the filter has a high amplification factor in the frequency region near the cut-off frequency fc, and input resistance characteristics deteriorate compared to a frequency with a low amplification factor. This problem is a problem unique to the active filter. As the attenuation characteristic of the active filter becomes steeper, the deterioration of the input resistance characteristic tends to increase. As shown in FIG. 4, near the cut-off frequency fc of the active filter, the anti-input characteristic of the active filter deteriorates in a V shape along the filter attenuation characteristic on one side. In FIG. 4, the horizontal axis represents frequency, and the vertical axis represents frequency characteristics (low-pass characteristics) of the active filter and input resistance characteristics.

<AGC convergence power and interference wave suppression ratio>
FIG. 5 shows the relationship between the AGC convergence power and the interference wave suppression ratio. In FIG. 5, the horizontal axis represents AGC convergence power (dBm), and the vertical axis represents the interference wave suppression ratio (dB). When the AGC convergence power, that is, the input power to the intermediate frequency low-pass filter (IFLPF) 6 is increased, the S / N ratio at the output of the intermediate frequency low-pass filter 6 can be kept high. Can be improved.

  However, if the input power to the intermediate frequency low-pass filter (IFLPF) 6 is increased too much, the input resistance characteristic of the intermediate frequency low-pass filter (IFLPF) 6 is exceeded, and the intermediate frequency low-pass filter (IFLPF) 6 is saturated. Therefore, the interference wave suppression ratio is significantly degraded as shown in FIG. That is, in the vicinity of the cutoff frequency of the intermediate frequency low-pass filter (IFLPF) 6, the anti-input characteristic of the intermediate frequency low-pass filter (IFLPF) 6 decreases in a V shape (see FIG. 4), and the frequency of the interference wave is intermediate. When the AGC convergence power is increased in the vicinity of the cutoff frequency of the frequency low-pass filter (IFLPF) 6, the input resistance characteristics are exceeded. In FIG. 5, the arrow line (interference wave of the interference wave) attached to the interference wave suppression ratio (solid line) The frequency deteriorates as shown in the vicinity of the cutoff frequency. Even when the frequency of the interference wave is higher than the cut-off frequency of the intermediate frequency low-pass filter (IFLPF) 6, if the AGC convergence power is increased too much, the degradation occurs as indicated by the arrow attached to the interference wave suppression ratio (broken line). To do.

<Improvement of interference wave suppression ratio>
In order to improve the interference wave suppression ratio of the receiver, it is necessary to make the attenuation characteristic of the intermediate frequency low-pass filter (IFLPF) 6 steep and improve the interference wave removal capability. However, when the steep attenuation characteristic is realized in the active filter, the deterioration of the input resistance characteristic near the cutoff frequency becomes large. For this reason, it is necessary to reduce the AGC convergence power, leading to a reduction in the interference wave suppression ratio. That is,
(A) To increase the interference wave suppression ratio, a low-pass active filter must have a steep attenuation characteristic.
(B) In an active filter having a steep attenuation characteristic, the deterioration of the input resistance characteristic near the cut-off frequency becomes large, and the interference wave suppression ratio decreases.

  The above (A) and (B) are in a trade-off relationship.

<Interference wave suppression ratio of related technology>
FIG. 6 shows a relationship between a desired wave and an interference wave input to the intermediate frequency low-pass filter 6 (the horizontal axis in FIG. 6 is frequency and the vertical axis is power). The interference wave in the vicinity of the desired wave on the frequency axis is referred to as “interference wave 1”.

  The output of the intermediate frequency low-pass filter (IFLPF) 6 corresponding to the interference wave 1 (attenuation characteristic at the IFLPF output indicated by the broken line in FIG. 6) is deteriorated in the input resistance characteristic of the intermediate frequency low-pass filter (IFLPF) 6. It is in the frequency band. An interference wave further away from the desired wave than the interference wave 1 on the frequency axis is referred to as an “interference wave 2”. The output of the intermediate frequency low-pass filter (IFLPF) 6 corresponding to the interference wave 2 is on the upper side (high frequency band) above the frequency band in which the anti-input characteristics of the intermediate frequency low-pass filter 6 deteriorate in a V shape. The intermediate frequency low-pass filter 6 is in a frequency band where the input resistance characteristics do not deteriorate.

  In the configuration of FIG. 3, since only one type of AGC setting can be taken, a certain AGC convergence power is continuously used. In the case of AGC setting in which the interference wave 1 is emphasized, the AGC convergence power is increased in a range not exceeding the deteriorated input resistance characteristic of the intermediate frequency low-pass filter 6 and the interference wave suppression ratio with respect to the interference wave 1 is improved. When the interference wave 2 becomes dominant with this AGC setting, there is a margin in the anti-input characteristics of the intermediate frequency low-pass filter 6, but since the AGC convergence power is constant, the margin is reduced by the interference wave suppression ratio. It cannot be used for improvement.

  In the case of the AGC setting in which the interference wave 2 is emphasized, since the input resistance characteristic of the intermediate frequency low-pass filter 6 with respect to the interference wave 2 is high, it is possible to set the AGC convergence power higher and suppress the interference wave with respect to the interference wave 2. The ratio can be improved.

  However, when the interference wave 1 becomes dominant with this AGC setting, the intermediate frequency low-pass filter 6 is saturated and the interference wave suppression ratio deteriorates.

  FIG. 7 schematically shows a change in the interference wave suppression ratio when the AGC convergence power changes. In FIG. 7, the horizontal axis represents the difference between the desired wave and interference wave channels, and the vertical axis represents the interference wave suppression ratio. When the AGC convergence power is large (broken line) and the difference between the desired wave and interference wave channels is approximately 2 or less in absolute value, the interference wave suppression ratio is significantly degraded compared to the case where the AGC convergence power is small (solid line). The channel difference is improved when the absolute value is 2 or more.

  As described above, in the semiconductor receiver shown in FIG. 3, only one type of AGC setting is possible, and it is impossible to know which of the interference wave 1 and the interference wave 2 is dominant.

  For this reason, there is no choice but to make a moderate AGC setting compatible with both the interference waves 1 and 2 in other words. As a result, a sufficiently high interference wave suppression ratio may not be obtained.

  According to the present invention, in the first aspect, a variable gain amplifier that receives an input signal and whose gain is varied by a control signal, a frequency converter that receives and converts the output signal from the variable gain amplifier, An active filter that receives an output signal of the frequency converter; a first circuit that detects power at a predetermined node before the active filter and generates a first signal for gain control of the variable gain amplifier; and A second circuit for detecting a power of an intermediate node of the active filter or a predetermined node after the active filter and generating a second signal for gain control of the variable gain amplifier; and the first and second circuits A first comparator that receives the first and second signals output from the comparator and compares the magnitudes of the first and second signals; and the first and second outputs that are output from the first and second circuits. A changeover switch that receives a signal, selects one of the first and second signals based on the comparison result of the comparator, and supplies the selected signal as the control signal for gain control of the variable gain amplifier. A receiver is provided.

According to the present invention, in the second aspect, a variable gain amplifier that is mounted on a semiconductor device and receives an input signal and whose gain is variable by a control signal, and a frequency conversion that receives an output signal from the variable gain amplifier. An automatic gain control method for a receiver, comprising: a frequency converter that performs an active filter that receives an output signal of the frequency converter,
Detecting power of a node in front of the active filter to generate a first signal for gain control of the variable gain amplifier;
Detecting a power of an intermediate node of the active filter or a node subsequent to the active filter to generate a second signal for gain control of the variable gain amplifier;
Comparing the magnitudes of the first and second signals;
An automatic gain control method is provided that selects one of the first and second signals based on the comparison result and supplies the selected signal as a control signal for gain control of the variable gain amplifier.

  According to the present invention, it is possible to realize an interference wave suppression ratio according to an interference wave frequency, and in particular, to improve an interference wave suppression ratio at a frequency that requires a high interference wave suppression ratio.

It is a figure which shows the structure of Embodiment 1 of this invention. It is a figure which shows the interference wave suppression ratio standard in various TV broadcasting. It is a figure which shows the structure of typical related technology. It is a figure which shows the attenuation | damping characteristic and anti-input characteristic of an intermediate frequency low-pass filter. It is a figure which shows AGC convergence power and interference wave suppression ratio. It is a figure which shows the desired wave and interference wave which are input into an intermediate frequency low-pass filter. It is a figure which shows the interference wave frequency and interference wave suppression ratio in related technology. It is a figure which shows the detection electric power in each electric power detector. It is a figure in case the desired wave and the interference wave 1 are received (AGC loop open). It is a figure in case the desired wave and the interference wave 1 are received (AGC loop close). It is a figure when the desired wave and the interference wave 2 are received (AGC loop open). It is a figure in case the desired wave and the interference wave 2 are received (AGC loop close). It is a figure which shows the structure of Embodiment 2 of this invention. It is a figure which shows the structure of Embodiment 3 of this invention. It is a figure which shows the circuit structural example of an active filter.

  An embodiment of the present invention will be described. In one of the preferred embodiments of the present invention (Preferred Modes), by devising the configuration of the AGC loop, the first interference wave (interference wave 1) in the vicinity of the desired wave is obtained in frequency (on the frequency axis). When it is dominant, the AGC convergence power is lowered, and when the second interference wave (interference wave 2) far from the desired wave is dominant in frequency, switching is performed to increase the AGC convergence power. Is configured to perform autonomously, and the input resistance characteristics of the intermediate frequency low-pass filter can always be fully utilized. As a result, resistance against interference waves can be increased. In order to realize the above, in the present invention, as a control voltage used for convergence of the automatic gain control (AGC) loop of the variable gain amplifier, the input power of the frequency converter (MIXER) (before the intermediate frequency low-pass filter) The first differential voltage between the output voltage of the first power detector (DET1) 8 for detecting the power) and the first reference voltage (Vref1) 9, and the power of the intermediate node of the intermediate frequency low-pass filter 6 Two difference voltages, that is, an output voltage of the second power detector (DET2) 11 to be detected and a second difference voltage of the second second reference voltage (Vref2) 12 are prepared.

  Then, the first and second differential amplifiers are differentially amplified by the first and second differential amplifiers (DIFFAMP1, 2) 10, 13, respectively, and the first and second differential amplifiers (DIFFAMP1, 2). A comparator (COMP) 14 for comparing the output voltages of the first and second differential amplifiers (DIFFAMP1, 2) 10, 13 based on the comparison result of the comparator 14. A changeover switch (SW) 15 for selecting one of the voltages is provided, and the voltage selected by the changeover switch (SW) 15 is supplied to the high frequency variable gain amplifier 3 as a control voltage for gain control.

  In the present embodiment, by setting the first reference voltage (Vref1) 9 and the second second reference voltage (Vref2) 12 to appropriate voltages, the interference wave 1 close to the desired wave is dominant on the frequency axis. AGC convergence power can be switched depending on whether the interference wave 2 that is far from the desired wave is dominant or not. For this reason, the AGC convergence power can be increased within a range where the interference wave 1 and the interference wave 2 do not exceed the input resistance characteristics of the active filter. As a result, according to the present invention, it is possible to realize an interference wave suppression ratio according to the interference wave frequency, which is difficult with the related art. Hereinafter, description will be made in accordance with a specific embodiment.

<Embodiment 1>
FIG. 1 is a diagram showing Embodiment 1 of the present invention. Referring to FIG. 1, the receiver of this embodiment is
A high frequency variable gain amplifier (RFVGA) 3 whose input is connected to the input 1;
A frequency converter (MIXIER) 4 whose input is connected to a high frequency variable gain amplifier (RFVGA) 3;
A local oscillator (LO) 5 for supplying an LO signal to a frequency converter (MIXER) 4;
An intermediate frequency low pass filter (IFLPF) 6 having an input connected to the output of the local oscillator (LO) 5 and an output connected to the output 2;
A first power detector (DET1) 8 whose input is connected to an input node of a frequency converter (MIXIER) 4;
A first reference voltage (Vref1) 9;
A first differential amplifier (DIFFAMP1) 10 having an inverting input and a non-inverting input connected to a first power detector (DET1) 8 and a first reference voltage (Vref1) 9;
A second power detector (DET2) 11 whose input is connected to an intermediate frequency low pass filter (IFLPF) 6;
A second reference voltage (Vref2) 12,
A second differential amplifier (DIFFAMP2) 13 having an inverting input and a non-inverting input connected to the output of the second power detector (DET2) 11 and the second reference voltage (Vref2) 12,
A comparator (COMP) 14 for inputting and comparing the output of the first differential amplifier (DIFFAMP1) 10 and the output of the second differential amplifier (DIFFAMP2) 13;
The output of the first differential amplifier (DIFFAMP1) 10 and the output of the second differential amplifier (DIFFAMP2) 13 are input, one is selected based on the comparison result in the comparator (COMP) 14, and a high frequency variable gain amplifier And a changeover switch (SW) 15 that supplies the (RFVGA) 3 as a control voltage for gain control.

  In the present embodiment, the second power detector (DET2) 11, the second reference voltage (Vref2) 12, the second differential amplifier (DIFFAMP2) 13, and the comparator (COMP) 14 are switched. A switch (SW) 15 is added to the configuration of FIG. In the following, description of the same components as those in FIG. 3 will be omitted as appropriate, and description will be made focusing on differences from the configuration in FIG.

  The second power detector (DET2) 11 detects the power of the intermediate node of the intermediate frequency low-pass filter (IFLPF) 6 and outputs a voltage corresponding thereto. As the intermediate node of the intermediate frequency low pass filter (IFLPF) 6, for example, a node that completely removes the interference wave 2 and does not completely remove the interference wave 1 is selected.

  The second reference voltage (Vref2) 12 is a reference voltage to be compared with the output voltage of the second power detector (DET2) 11.

  The second differential amplifier (DIFFAP2) 13 outputs a difference voltage between the output voltage of the second power detector (DET2) 11 and the second reference voltage (Vref2) 12.

  The comparator (COMP) 14 receives the output voltages of the first and second differential amplifiers (DIFFAMP1, 2) 10, 13, so that the larger voltage is selected by the changeover switch (SW) 15. A switching control signal is output. The changeover switch (SW) 15 is one of the output voltages of the first and second differential amplifiers (DIFFAMP1, 2) 10, 13 based on the switching control signal from the comparator (COMP) 14 (the one with the higher voltage). Is supplied to the high-frequency variable gain amplifier 3 as a control voltage.

  FIGS. 8A and 8B are diagrams schematically illustrating the spectrum of signals detected by the first power detector (DET1) 8 and the second power detector (DET2) 11 (horizontal). The axis is frequency and the vertical axis is power). 8A shows the power spectrum in the frequency domain of the MIXER input signal detected by the first power detector (DET1) 8, and FIG. 8B shows the second power detector (DET2) 11. Represents the power spectrum in the frequency domain of the signal of the IFLPF intermediate node detected by.

  Although the interference wave 2 can be sufficiently attenuated as an intermediate node of the intermediate frequency low-pass filter 6 (see the attenuation characteristics at the IFLPF intermediate node in FIGS. 8A and 8B), the interference wave 1 is not sufficiently attenuated. Node is selected. In this way, when an interference wave 1 having a frequency close to that of the desired wave (an interference wave near the cutoff frequency) is input, the power detected by the second power detector (DET2) 11 is as shown in FIG. As shown, the residual power of the interference wave 1 is included.

  On the other hand, when the interference wave 2 having a frequency different from that of the desired wave is input, it is sufficiently attenuated at the intermediate node of the intermediate frequency low-pass filter 6 and is detected by the second power detector (DET2) 11. The remaining power of the interference wave 2 is hardly included in the power to be generated.

  Further, as shown in FIG. 8A, in the first power detector (DET1) 8 that detects the power of the input signal to the frequency converter (MIXER) 4, the desired wave, the interference wave 1, and the interference wave 2 All power is detected.

<When desired wave and interference wave 1 are input>
9 and 10 show the relationship between the input power (Pin) and the power detector output voltage (Vout_det) in the first and second power detectors (DET1, DET2) 8 and 11 in FIG. 1 (horizontal axis). : Pin, vertical axis: Vout_det). Vref1 and Vref2 on the vertical axis are the first and second reference voltages in FIG.

  FIG. 9 shows a relationship in which the output voltage Vout_det of the power detector increases in proportion to the input power (Pin) when the AGC loop is open.

  FIG. 10 shows a case where the AGC loop is closed. When Vout_det reaches the reference voltage, the negative feedback AGC loop works, and in the input power range beyond that, Vout_det = reference voltage (Vref). The gain of the high frequency variable gain amplifier 3 is adjusted.

  When the desired wave and the interference wave 1 are input, the interference wave 1 among the signals detected by the second power detector (DET2) 11 is slightly attenuated up to the intermediate node of the intermediate frequency low-pass filter 6. Therefore, the output voltage Vout_det2 of the second power detector (DET2) 11 is slightly lower than the output voltage Vout_det1 of the first power detector (DET1) 8.

  As shown in FIG. 10, by setting the second reference voltage (Vref2) 12 lower than the first reference voltage (Vref1) 9, the output voltage Vout_det2 of the second power detector (DET2) 11 is set. The AGC loop works so that the second reference voltage (Vref2) 12 is balanced (Vout_det2 = Vref2) (the solid line indicated by the arrow of @ DET2 in FIG. 10).

  In this case, Vout_det1 (solid line indicated by the arrow of @ DET1 in FIG. 10) does not reach the first reference voltage (Vref1) 9 (Vout_det1 <Vref1), and is constant at a lower voltage. Note that the difference between the second reference voltage (Vref2) 12 and the first reference voltage (Vref1) 9 is the difference between the output voltage Vout_det1 of the first power detector (DET1) 8 and the second power detection at the same input power. The output voltage Vout_det2 of the device (DET2) 11 needs to be set larger than the difference.

  When the desired wave and the interference wave 2 are input, FIGS. 11 and 12 show the relationship between the input power (Pin) and the power detector output voltage (Vout_det).

  FIG. 11 shows a case where the AGC loop is open. FIG. 12 shows a case where the AGC loop is closed.

  When the desired wave and the interference wave 2 are input, the interference wave 2 is sufficiently attenuated by the intermediate frequency low-pass filter 6, and the output voltage Vout_det2 of the second power detector (DET2) 11 is sufficiently lower than Vout_det1. Become. Therefore, the AGC loop works so that the output voltage Vout_det1 of the first power detector (DET1) 8 and the reference voltage (Vref1) 9 are balanced (see the solid line indicated by the arrow of @ DET1 in FIG. 12). The output voltage Vout_det2 of the second power detector (DET2) 11 does not reach the second reference voltage (Vref2) 12, and becomes constant at a voltage lower than that (indicated by the arrow of @ DET2 in FIG. 12) See solid line).

  In this case, the output voltage Vout_det1 of the first power detector (DET1) 8 is higher than when the interference wave 1 is input, and the output power of the frequency converter (MIXER) 4, that is, the intermediate frequency low frequency range. The input power to the pass filter 6 increases.

  The operation of the above embodiment is summarized as follows.

<When receiving desired wave + interference wave 1>
The AGC loop
Vout_det2 = second reference voltage (Vref2) 12
Therefore, the AGC convergence power is determined by the second reference voltage (Vref2) 12.

  Therefore, the input power of the intermediate frequency low-pass filter 6 is controlled by the second reference voltage (Vref2) 12. The second reference voltage (Vref2) 12 is adjusted so that the interference wave 1 does not exceed the deteriorated input resistance characteristic of the intermediate frequency low-pass filter 6.

<When receiving desired wave + interference wave 2>
The AGC loop
Vout_det1 = first reference voltage (Vref1) 9
Therefore, the AGC convergence power is determined by the first reference voltage (Vref1) 9.

  Therefore, the input power of the intermediate frequency low-pass filter 6 is controlled by the first reference voltage (Vref1) 9. The first reference voltage (Vref1) 9 is adjusted so that the interference wave 2 does not exceed the non-degraded input resistance characteristic of the intermediate frequency low-pass filter 6.

  According to the present embodiment, the first reference voltage (Vref1) 9 and the second reference voltage (Vref2) 12 can be set independently of each other. For this reason, according to the present invention, the AGC convergence power for the interference wave 1 and the interference wave 2 can be set independently.

  Therefore, the optimum AGC convergence power can be autonomously obtained for each of the case where the interference wave 1 is dominant and the case where the interference wave 2 is dominant, so that a high interference wave suppression ratio can be always obtained.

<Embodiment 2>
FIG. 13 is a diagram showing a configuration of the second exemplary embodiment of the present invention. The difference between the present embodiment and the first embodiment is that an AD converter (Analog to Digital Converter, ADC) 16 and a digital filter 17 are provided after the intermediate frequency low-pass filter (IFLPF) 6. The input of the second power detector (DET2) 2 is connected to an intermediate node of a digital filter.

  The operation of the second embodiment of the present invention will be described. The basic operation is the same as in the first embodiment.

When the interference signal 1 is included in the received signal, the output voltage Vout_det2 of the second power detector (DET2) 11 is
Vout_det2 = second reference voltage (Vref2) 12
The AGC loop of the second power detector (DET2) -second differential amplifier (DIFFAMP2) works so that

When the interference signal 1 is not included in the received signal, the output voltage Vout_det1 of the first power detector (DET1) 8 is
Vout_det1 = first reference voltage (Vref1) 9
Thus, the AGC loop of the first power detector (DET1) -first differential amplifier (DIFFAMP1) works.

  By appropriately setting the first reference voltage (Vref1) 9 and the second reference voltage (Vref2) 12, the AGC convergence power is within a range in which the interference wave 1 and the interference wave 2 do not exceed the input resistance characteristics of the active filter. The interference wave suppression ratio corresponding to the interference wave frequency can be realized.

  In the second embodiment, the digital filter 17 plays a part of the role of removing the interference wave. Since the digital filter 17 is not an active filter, the input resistance characteristics are not deteriorated.

  The intermediate frequency low-pass filter (IFLPF) 6 is composed of an active filter. For this reason, as in the first embodiment of FIG. 1, there is a problem of deterioration of the input resistance near the cutoff frequency. However, a part of the attenuation characteristic of the intermediate frequency low-pass filter 6 is a digital filter. Therefore, compared with the first embodiment, the attenuation characteristic of the intermediate frequency low-pass filter 6 can be set more gently, and the deterioration of the input resistance characteristic can be reduced. This means that the input power of the intermediate frequency low-pass filter 6 is increased, and the interference wave suppression ratio of the entire receiver is improved.

  Further, by setting the input to the second power detector (DET2) 11 as an intermediate node of the digital filter 17, the input to the second power detector (DET2) 11 is set to the intermediate node of the active filter 6 as an input. Compared to the first embodiment, variation in filter attenuation characteristics can be reduced.

  Therefore, since the input power (Pin) vs. the second power detector output voltage (Vout_det2) is stabilized without being affected by the manufacturing variation of the semiconductor device, a more accurate AGC loop switching operation can be realized. .

<Embodiment 3>
FIG. 14 is a diagram showing the configuration of the third exemplary embodiment of the present invention. Referring to FIG. 14, the present embodiment is different from the first embodiment of FIG. 1 in that the first power detector (DET1) 8 is different from the first embodiment in the frequency converter ( In this embodiment, the output is changed to the output of the frequency converter (MIXER) 4, and hence the input of the intermediate frequency low-pass filter (IFLPF) 6.

  In the first embodiment, the following two types of AGC voltages are prepared and switched according to the frequency relationship between the desired wave and the interference wave.

  (1) Output voltage and first reference voltage of the first power detector (DET1) for detecting the input power of the frequency converter (MIXER) 4 (the power preceding the intermediate frequency low pass filter (IFLPF) 6) (Vref1) 9 differential voltage.

  (2) The difference voltage between the output voltage of the second power detector (DET2) that detects the power of the intermediate node of the intermediate frequency low-pass filter (IFLPF) 6 and the second reference voltage (Vref2) 12.

  In this case, (1) is a necessary condition for the power before the intermediate frequency low-pass filter (IFLPF) 6, the input power of the frequency converter (MIXER) 4, and the intermediate frequency low-pass filter (IFLPF) 6. The same effect can be achieved by using either of the input power. Also in the third embodiment of the present invention, the same effect as in the first embodiment can be expected.

  FIG. 15 is a diagram showing a configuration example of an active filter constituting the intermediate frequency low-pass filter (IFLPF) 6 in each of the embodiments. In the example of FIG. 15, the intermediate frequency low-pass filter 6 includes five operational amplifiers OP1 to OP5, and the intermediate node corresponds to the differential output of the third operational amplifier OP3. For example, an operational amplifier, an input resistor, and a feedback capacitor constitute a transfer function (-K / s; a capacitor is 1 and an input resistor is 1 / K), and a feedback resistor and a capacitor connected in parallel with one operational amplifier and an input resistor are A primary transfer function (-K / (s + p1); input resistance is 1, capacitance is 1 / K, and feedback resistance is K / p1) is configured. More specifically, the intermediate frequency low-pass filter (IFLPF) 6 includes operational amplifiers OP1 to OP5 cascaded in five stages, resistors R1 to R20 and capacitors C1 to C10 constituting each stage. The first stage amplifier OP1 is connected to the input nodes IN1 and IN2 of the intermediate frequency low-pass filter IFLPF via the resistors R1 and R2, and the output signal of the final stage amplifier OP5 is connected to the output nodes OT1 and OT2. . The output signal of the third stage amplifier OP3 is connected to the intermediate nodes MN1 and MN2. Even if the interference wave 1 and the desired wave are input to the input nodes IN1 and IN2 of the intermediate frequency low-pass filter IFLPF, the five-stage total has sufficient attenuation characteristics. Therefore, the output nodes OT1 and OT2 Only waves can be filtered and output. However, in the intermediate nodes MN1 and MN2 to which the output signal of the third stage amplifier OP3 is connected, the interference wave 1 such as the interference wave 1 in FIG. Output as an included signal. On the other hand, when the interference wave 2 is input to the input nodes IN1 and IN2, the interference wave 2 is removed at the stage of the intermediate nodes MN1 and MN2, and only the desired wave is output.

  The intermediate nodes MN1 and MN2 of the intermediate frequency low-pass filter IFLPF are connected to the power detector DET2 and the output nodes OT1 and OT2 to the output 2 in FIG. In FIG. 8, the intermediate nodes MN1 and MN2 and the output nodes OT1 and OT2 are described as outputting a pair of complementary signals. However, in FIG. 1, a pair of complementary signals is a single signal. As a simplified description.

  The configuration shown in FIG. 15 is merely an example, but the interference wave 2 is sufficiently attenuated by drawing out between the input and the output as an intermediate node in this way, but the node is not sufficiently attenuated with respect to the interference wave 1. Can be created.

  In the second embodiment of FIG. 13, the power of the intermediate node of the digital filter 17 is detected by the second power detector (DET2). The intermediate node in this case has various configurations depending on the configuration of the digital filter 17. It can be realized with a terminal. Considering the case where the digital filter 17 is constituted by a two-stage cascade filter as an example, if the output terminal of the first-stage filter is taken out as an intermediate node of the digital filter 17, information necessary for the present invention can be extracted. .

  The above-described embodiment has the following effects.

  It is possible to realize an interference wave suppression ratio according to the interference wave frequency, and particularly to improve the interference wave suppression ratio at a frequency (interference wave 2) that requires a high interference wave suppression ratio.

  In the present invention, attention is paid to deterioration of input resistance characteristics of an active filter built in a semiconductor receiver, and an object is to improve the interference wave suppression ratio deterioration of the receiver caused by the deterioration. On the other hand, Patent Document 1 (Japanese Patent Laid-Open No. 2003-218711) searched by the prior art document search assumes a ceramic filter as a filter provided in the IF region, and is an invention different from the subject of the present invention. . In the present invention, the AGC loop is switched according to the intensity of the interference wave near the cutoff frequency where the input resistance characteristics of the active filter provided in the IF region of the semiconductor receiver deteriorate, thereby preventing the saturation of the active filter and preventing interference. The wave suppression ratio is improved. A node that generates an AGC voltage, and an interference wave near the active filter cutoff frequency cannot be sufficiently attenuated, but an interference wave of an adjacent frequency is sufficiently attenuated (an intermediate node of an intermediate frequency low-pass filter). ) Must be selected.

  In Patent Document 1 (Japanese Patent Application Laid-Open No. 2003-218711), the control of the AGC loop is switched between the case where the interference wave existing in the IF region of the receiver exists in the filter pass band and the case where the interference wave exists outside the pass band, The operation of preventing deterioration of reception sensitivity is performed. In the present invention, the AGC voltage generated from the power at the input of the frequency converter (MIXER) is compared with the AGC voltage generated from the intermediate node power of the intermediate frequency low-pass filter, and the magnitude relationship between the reference voltages. The AGC loop is selected from the above. In Patent Document 1 (Japanese Patent Laid-Open No. 2003-218711), two types of AGC voltages are generated from the mixer input and the bandpass filter 1 output, and the larger AGC voltage is used.

  It should be noted that the disclosures of the above patent documents are incorporated herein by reference. Within the scope of the entire disclosure (including claims) of the present invention, the embodiments and the embodiments can be changed and adjusted based on the basic technical concept. Various combinations and selections of various disclosed elements are possible within the scope of the claims of the present invention. That is, the present invention of course includes various variations and modifications that could be made by those skilled in the art according to the entire disclosure including the claims and the technical idea.

1 input 2 output 3 high frequency variable gain amplifier (RFVGA)
4 Frequency converter (MIXER)
5 Local oscillator (LO)
6 Intermediate frequency low-pass filter (IFLPF) (active filter)
7, 7A, 7B, 7C Automatic gain control loop 8 First power detector (DET1) (Power detector (DET))
9 First reference voltage (Vref1) (reference voltage (Vref))
10 First differential amplifier (DIFFAMP1) (Differential amplifier (DIFFAMP))
11 Second power detector (DET2)
12 Second reference voltage (Vref2)
13 Third differential amplifier (DIFFAMP2)
14 Comparator (COMP)
15 Changeover switch (SW)
16 Analog-to-digital converter (ADC)
17 Digital filter

Claims (9)

A variable gain amplifier that receives an input signal and whose gain is variable by a control signal;
A frequency converter that receives and converts the output signal from the variable gain amplifier; and
An active filter for receiving an output signal from the frequency converter;
A first circuit for detecting a power of a predetermined node in front of the active filter and generating a first signal for gain control of the variable gain amplifier;
A second circuit for detecting a power of an intermediate node of the active filter and generating a second signal for gain control of the variable gain amplifier;
A comparator that receives the first and second signals output from the first and second circuits and compares the magnitudes of the first and second signals;
The first and second signals output from the first and second circuits are received, one of the first and second signals is selected based on the comparison result of the comparator, and the gain is variable. A change-over switch supplied as the control signal for gain control of the amplifier;
Equipped with a receiver. The first circuit includes a first power detector that detects power of the predetermined node before the active filter;
A first differential amplifier that differentially inputs an output of the first power detector and a first reference voltage;
With
The second circuit includes a second power detector for detecting power of the intermediate node of the active filter;
A second differential amplifier for differentially inputting an output of the second power detector and a second reference voltage;
With
The comparator compares the output voltages of the first and second differential amplifiers;
The receiver according to claim 1, wherein the changeover switch selectively outputs a larger voltage of the output voltages of the first and second differential amplifiers. A variable gain amplifier that receives an input signal and whose gain is variable by a control signal;
A frequency converter that receives and converts the output signal from the variable gain amplifier; and
An active filter for receiving an output signal from the frequency converter;
An analog-digital converter that converts an analog output signal of the active filter into a digital signal;
A digital filter for filtering the output signal of the analog-digital converter;
A first circuit for detecting a power of a predetermined node in front of the active filter and generating a first signal for gain control of the variable gain amplifier ;
A second circuit for detecting a power of an intermediate node of the digital filter and generating a second signal for gain control of the variable gain amplifier ;
A comparator that receives the first and second signals output from the first and second circuits and compares the magnitudes of the first and second signals;
The first and second signals output from the first and second circuits are received, one of the first and second signals is selected based on the comparison result of the comparator, and the gain is variable. A change-over switch supplied as the control signal for gain control of the amplifier;
With
The first circuit includes a first power detector that detects power of the predetermined node before the active filter;
A first differential amplifier that differentially inputs an output of the first power detector and a first reference voltage;
With
The second circuit includes a second power detector for detecting power of an intermediate node of the digital filter;
A second differential amplifier for differentially inputting an output of the second power detector and a second reference voltage;
With
The comparator compares the output voltages of the first and second differential amplifiers;
The change-over switch is a receiver that selectively outputs the larger voltage of the output voltages of the first and second differential amplifiers. The predetermined node before the active filter is:
An input node of the frequency converter;
The receiver according to any one of claims 1 to 3, wherein the receiver is any one of connection nodes between an output of the frequency converter and an input of the analog filter.   The receiver according to any one of claims 2 to 4, wherein the active filter is a low-pass filter. The second reference voltage is lower than the first reference voltage;
When the desired wave in the pass band of the low-pass active filter and the first interference wave closer to the cutoff frequency of the active filter are received, the output voltage of the second power detector is Controlled to be equal to the second reference voltage,
The input power to the low-pass active filter is determined by the second reference voltage;
When receiving the desired wave in the pass band of the low pass type active filter and the second interference wave that is separated from the cutoff frequency of the active filter than the first interference wave, the first power The output voltage of the detector is controlled to be equal to the first reference voltage;
The receiver according to claim 5, wherein input power to the low-pass active filter is determined by the first reference voltage. When the input power to the low-pass active filter is determined by the second reference voltage, the first interference wave does not exceed the input resistance characteristics of the low-pass active filter. The second reference voltage is adjusted;
When the input power to the low-pass active filter is determined by the first reference voltage, the second interference wave does not exceed the input resistance characteristics of the low-pass active filter. The receiver of claim 6, wherein the first reference voltage is adjusted.   A semiconductor device comprising the receiver according to claim 1. A variable gain amplifier that is mounted on a semiconductor device and whose input signal is input and whose gain is variable by a control signal, a frequency converter that receives and converts an output signal from the variable gain amplifier, and a frequency converter from the frequency converter An active filter for receiving an output signal, and a receiver automatic gain control method comprising:
Detecting power of a predetermined node before the active filter to generate a first signal for gain control of the variable gain amplifier;
Detecting a power of an intermediate node of the active filter to generate a second signal for gain control of the variable gain amplifier;
Comparing the magnitudes of the first and second signals;
An automatic gain control method, wherein one of the first and second signals is selected based on the comparison result, and the selected signal is used as a control signal for gain control of the variable gain amplifier.

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