JPH09298475A - Receiving circuit - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a receiving circuit whose characteristic is less deteriorated due to intermodulation of interference waves. SOLUTION: After an output signal of a MIX 5 converted into an intermediate frequency is amplified by a gain control AMP 8 so as to make the output constant, the resulting signal is detected by a quadrature detector 9, from which an I-signal 12 and a Q-signal 13 are obtained. The I-signal 12 and the Q-signal 13 are filtered respectively by LPFs 10, 11. Simultaneously the I-signal 12 and the Q-signal 13 are filtered by HPFs 18, 19, from which only a interference wave component is extracted. The I-signal 12 and the Q-signal 13 filtered by the HPFs 18, 19 are respectively A/D-converted by A/D converters 20, 21 and the level is detected by calculating the root of square sum of the I- and Q- components at a level detection circuit 22. The signal whose level is detected is subjected to integration in terms of time by an integration circuit 23 and the level is compared with a reference level and decided by a level decision circuit 24 and its output is used to vary the gain of a low noise AMP control circuit.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a receiver circuit of a receiver used for digital mobile communication or the like, and more particularly to a receiver circuit with less deterioration of reception characteristics due to intermodulation of interfering waves.

[0002]

2. Description of the Related Art As shown in FIG. 7, a receiver circuit of a receiver used in a conventional digital mobile communication or the like includes an antenna 1 for receiving a signal and a bandpass filter 2 for filtering a signal received by the antenna 1. A low noise amplifier 3 for amplifying the output of the band pass filter 2, and the low noise amplifier 3
, A mixer 5 for frequency-converting the output signal of the bandpass filter 4, an oscillator 6, a bandpass filter 7 for filtering the output of the mixer 5, and a bandpass filter A gain control amplifier 8 for varying the gain of the output of 7 by a control voltage; a quadrature detector 9 for quadrature detection of the output of the gain control amplifier 8;
The low-pass filter 10 and the low-pass filter 11 for filtering the output I signal 12 and the output Q signal 13 of the quadrature detector 9 are provided.

In this receiving circuit, the signal received by the antenna 1 is filtered by the bandpass filter 2, then amplified by the low noise amplifier 3, filtered by the bandpass filter 4, and output from the oscillator 6 by the mixer 5. The signal is frequency-converted into an intermediate frequency band, filtered by the bandpass filter 7, amplified by the gain control amplifier 8, and then quadrature-detected by the quadrature detector 9 to obtain output I signal 12 and Q signal 13.

[0004]

However, in the above conventional receiving circuit, when two or more interfering waves having a frequency relationship that causes intermodulation in the received signal are received at the same time,
When the frequency is converted into the intermediate frequency band by the mixer, there is a problem that the interfering wave drops into the band of the desired reception signal due to the intermodulation by the interfering waves of two or more waves, the interfering wave ratio of the receiving signal deteriorates, and the receiving characteristic deteriorates. there were. The present invention solves these conventional problems, and an object of the present invention is to provide a receiving circuit in which the deterioration of receiving characteristics due to intermodulation of interfering waves is small.

[0005]

In order to solve the problems of the conventional receiving circuit, the receiving circuit of the present invention is a circuit for detecting the interfering wave level in the I signal and the Q signal detected by the quadrature detector. Is provided, and the gain of the reception frequency band from the antenna to the mixer is variably controlled according to the level of the interference wave. As a result, the invention according to claim 1 of the present invention comprises an antenna for receiving a radio signal, an amplifier for amplifying the received signal, a filter for filtering the received signal,
It has a mixer that frequency-converts the received signal into an intermediate frequency band, an amplifier that amplifies the signal in the intermediate frequency band, a filter that filters the signal in the intermediate frequency band, and a quadrature detector that quadrature-detects the signal in the intermediate frequency band. In the receiving circuit, a high-pass filter that filters the output I signal and the output Q signal of the quadrature detector, an AD converter that performs analog / digital conversion of the output I signal and the output Q signal of the high-pass filter, and the AD conversion A level detection circuit for performing level detection from the I output and Q output of the container, an integration circuit for time integration of the output of the level detection circuit, a level determination circuit for comparing the output of the integration circuit with a reference value, A low noise amplifier gain control circuit that varies the gain in the reception frequency band according to the output data of the level determination circuit, The path has a first switch for branching the received signal of the antenna into two, a low noise amplifier for amplifying the branched signal, and a second switch for switching the output of the low noise amplifier and the output signal of the first switch. And a third resistor and a fixed resistor for switching the input load of the low-noise amplifier, and on / off-controls each switch by a control signal of the level determination circuit to variably control the gain. , The gain of the low-noise amplifier gain control circuit is varied according to the level of the interfering wave in the received signal to minimize the deterioration of the receiving characteristic due to the intermodulation of the interfering wave.

According to a second aspect of the present invention, the low noise amplifier gain control circuit includes the low noise amplifier, a fourth switch for bypassing the low noise amplifier, and a power source for the low noise amplifier. And a fixed resistor for switching the load of the input of the low noise amplifier, the ON / OFF control of each switch according to the control signal of the level determination circuit, and the gain. Is variably controlled, and has a function of reducing the circuit current when the low noise amplifier is bypassed by providing a fifth switch in the power source of the low noise amplifier.

According to a third aspect of the present invention, the low noise amplifier gain control circuit comprises the low noise amplifier, a gain control amplifier for varying the gain of an output signal of the low noise amplifier according to a control voltage, and the level. The D / A converter for converting the output data of the judgment circuit into digital / analog and the low-pass filter for filtering the output voltage of the D / A converter, and the control signal for the level judgment circuit includes the D / A converter. Digital / analog conversion is performed by a converter, the gain of the gain control amplifier is controlled by the control voltage filtered by the low-pass filter, and the gain is variably controlled. A gain control amplifier is provided at the output of the low noise amplifier. , Has the effect of continuously varying the gain.

According to a fourth aspect of the present invention, an antenna for receiving a radio signal, an amplifier for amplifying the received signal, a filter for filtering the received signal, and a mixer for frequency-converting the received signal into an intermediate frequency band. An amplifier for amplifying a signal in the intermediate frequency band, a filter for filtering the signal in the intermediate frequency band, and a quadrature detector for quadrature detecting the signal in the intermediate frequency band, wherein an output I signal of the quadrature detector A high-pass filter for filtering, an AD converter for analog / digital converting the output I signal of the high-pass filter, and an integrating circuit for time-integrating the output of the AD converter,
The low noise amplifier gain control circuit comprises: a level judgment circuit for comparing the output of the integrator circuit with a reference value; and a low noise amplifier gain control circuit for varying the gain in the reception frequency band according to the output data of the level judgment circuit. A control circuit includes a first switch that branches the reception signal of the antenna into two, a low-noise amplifier that amplifies the branched signal, and a second switch that switches the output of the low-noise amplifier and the output signal of the first switch.
Switch, a third switch for switching the load of the input of the low noise amplifier, and a fixed resistor. Each switch is turned on / off by a control signal of the level determination circuit.
It is off-controlled and the gain is varied, and has an effect of detecting the interfering wave level only by the I signal output of the quadrature detector.

According to a fifth aspect of the present invention, the low noise amplifier gain control circuit includes the low noise amplifier, a fourth switch for bypassing the low noise amplifier, and a power source of the low noise amplifier is turned on / off. A third switch for switching the input load of the low-noise amplifier and the fixed resistor, and ON / OFF-controls each switch by a control signal of the level determination circuit,
The gain is variably controlled. The interfering wave level is detected only by the I signal output of the quadrature detector, and the power switch of the low noise amplifier is provided to reduce the circuit current when bypassing the low noise amplifier. is there.

According to a sixth aspect of the present invention, the low noise amplifier gain control circuit comprises the low noise amplifier, a gain control amplifier for varying the gain of an output signal of the low noise amplifier according to a control voltage, and the level. It comprises a D / A converter for digital / analog converting the output data of the decision circuit and a low pass filter for filtering the output voltage of the D / A converter, and the control signal of the level decision circuit is the D / A. Digital / analog conversion is performed by a converter, the gain of the gain control amplifier is controlled by the control voltage filtered by the low-pass filter, and the gain is variably controlled. I signal output of a quadrature detector for interfering wave level detection The gain control amplifier is provided at the output of the low noise amplifier, and the gain is continuously varied.

[0011]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described below with reference to FIGS. 1 to 6.

(First Embodiment) As shown in FIG. 1, the receiving circuit of the first embodiment has an antenna 1 for receiving a radio signal and a bandpass filter 2 for filtering a signal received by the antenna 1. , A first switch 14 for switching the output of the bandpass filter 2 to two systems, and a first switch 14
A low noise amplifier 3 for amplifying the output, and a second switch for switching between the output of the low noise amplifier 3 and the other one output of the first switch 14.
Switch 15, a third switch 16 and a fixed resistor 17 that switch the input load of the low-noise amplifier 3, a bandpass filter 4 that filters the output of the second switch 15, and an output of the bandpass filter 4. Of the output of the oscillator 6, a mixer 5 for filtering the output of the mixer 5, a bandpass filter 7 for filtering the output of the mixer 5, a gain control amplifier 8 for variably controlling the output of the bandpass filter 7, and an output of the gain control amplifier 8. Quadrature detector 9 for quadrature detection, low-pass filter 10 and low-pass filter 11 for filtering I signal 12 and Q signal 13 output from quadrature detector 9, and I signal 12 and Q signal 13 output from quadrature detector 9 A high-pass filter 18 and a high-pass filter 19 for filtering the signal, and an AD converter 20 and an AD converter for AD-converting the outputs of the high-pass filter 18 and the high-pass filter 19.
21, a level detector 22 for detecting the levels of the outputs of the AD converter 20 and the AD converter 21, an integration circuit 23 for time integration of the output of the level detector 22, and a level determination for comparing the outputs of the integration circuit 23 And a circuit 24. The control signal 25 controls ON / OFF of the third switch 16 according to the level of the interfering wave detected by the level detection circuit 22 and the integration circuit 23,
Reference numeral 26 denotes the first switch 14 and the second switch 15 according to the interfering wave levels detected by the level detection circuit 22 and the integration circuit 23.
On / off control.

Next, the operation of this receiving circuit will be described. First, the signal received by the antenna 1 is filtered by the bandpass filter 2, and the low noise composed of the first switch 14, the low noise amplifier 3, the second switch 15, the third switch 16 and the fixed resistor 17 is provided. The variable gain is controlled by the amplifier control circuit.
The operation of the low noise amplifier control circuit will be described later.

Next, the signal whose gain is changed by the low noise amplifier control circuit is filtered by the bandpass filter 4,
The mixer 5 mixes the output signal of the oscillator 6 and frequency-converts it into an intermediate frequency band. The output signal of the mixer 5 converted to the intermediate frequency is filtered by the bandpass filter 7, amplified by the gain control amplifier 8 so that the output becomes constant, and then quadrature detected by the quadrature detector 9 to obtain the I signal.
12 and Q signal 13 are obtained.

The I signal 12 and the Q signal 13 are low-pass filters.
It is filtered by 10 and low-pass filter 11 and output. At the same time, the I signal 12 and the Q signal 13 are respectively high-pass filtered.
It is filtered by 18 and the high pass filter 19, and only the interfering wave component is extracted. High-pass filter 18 and high-pass filter 19
The I signal 12 and the Q signal 13 which have been filtered are subjected to analog / digital conversion by the AD converter 20 and the AD converter 21, respectively, and the level detection circuit 22 takes the square root of the sum of squares of the I component and the Q component. The level is detected by.

The signal whose level is detected by the level detection circuit 22 is time-integrated by the integration circuit 23, and the level judgment circuit 24 makes a comparison judgment with the reference level. The level judgment circuit 24 controls the low noise amplifier control circuit as follows according to the level reference values I1 and I2 (I1 <I2).

When the input level of the level determination circuit 24, that is, the interference wave level I input to the antenna 1 is I <I1, the low noise amplifier control circuit includes the first switch 14 and the second switch 14.
The switch 15 is set to the low noise amplifier 3 side by the control signal 26, the third switch 16 is opened by the control signal 25, and the input signal is amplified by the low noise amplifier 3 and output.

Next, the input level of the level determination circuit 24, that is, the interference wave level I input to the antenna 1 is I1 <I
In the case of <I2, the low noise amplifier control circuit sets the first switch 14 and the second switch 15 to the low noise amplifier 3 side by the control signal 26 and closes the third switch 16 by the control signal 25. The load of the fixed resistor 17 is added to the input of the noise amplifier 3, and the input signal of the low noise amplifier 3 is attenuated by the attenuation amount according to the resistance value of the fixed resistor 17, amplified by the low noise amplifier 3, and output.

Next, the input level of the level determination circuit 24, that is, the level I of the interference wave input to the antenna 1 is I> I2.
In the case of, the low noise amplifier control circuit is
The second switch 15 is set to the bypass line side by the control signal 26, bypasses the low noise amplifier 3, and is output.

Therefore, the input level to the mixer 5 is controlled by varying the gain of the low noise amplifier control circuit according to the level of the interfering wave input to the antenna 1, and the intermodulation by the interfering wave input of two or more waves is performed. It is possible to minimize the deterioration of the reception characteristic due to.

(Second Embodiment) As shown in FIG. 2, the receiving circuit of the second embodiment has a low noise amplifier control circuit for bypassing the low noise amplifier 3 and the low noise amplifier 3. No. 4 switch 28, fifth switch 27 for turning on / off the power of the low noise amplifier 3, the third switch 16 for switching the input load of the low noise amplifier 3, and the fixed resistor.
It is composed of 17 to reduce the circuit current of the low noise amplifier 3. Other configurations are the same as those in the first embodiment.

In this receiving circuit, the low noise amplifier control circuit is controlled by the level reference values I1 and I2 (I1 <I2) of the level determination circuit 24 as follows.

When the input level of the level determination circuit, that is, the interference wave level I input to the antenna 1 is I <I1, the low noise amplifier control circuit opens the fourth switch 28 by the control signal 30, The switch 16 is opened by the control signal 25, the fifth switch 27 is closed, and the power source of the low noise amplifier 3 is turned on. At this time, the signal input to the low noise amplifier control circuit is amplified by the low noise amplifier 3 and output.

Next, the input level of the level determination circuit, that is, the interference wave level I input to the antenna 1 is I1 <I <
In the case of I2, the low noise amplifier control circuit opens the fourth switch 28 by the control signal 30 and sets the fifth switch
27 is closed and the low noise amplifier 3 is turned on,
The third switch 16 is closed by the control signal 25, the load of the fixed resistor 17 is added to the input of the low noise amplifier 3, and the input signal of the low noise amplifier 3 is attenuated by the attenuation amount according to the resistance value of the fixed resistor 17. And is amplified by the low noise amplifier 3 and output.

Next, when the input level of the level judgment circuit, that is, the interference wave level I input to the amplifier 1 is I> I2, the low noise amplifier control circuit opens the third switch 16 by the control signal 25. , The input signal is bypassed by closing the fourth switch 28 with the control signal 30 and the fifth switch 27 is opened with the control signal 29, and the low noise amplifier 3 is turned off, and the low noise amplifier during signal bypass Has eliminated the effect of. At this time, the input signal is bypassed by the fourth switch 28 and output.

Therefore, the input level to the mixer 5 is controlled by varying the gain of the low noise amplifier control circuit according to the level of the interfering wave input to the antenna 1, and the intermodulation by the interfering wave input of two or more waves is performed. It is possible to minimize the deterioration of the reception characteristic due to, and to reduce the circuit current by turning off the power supply of the low noise amplifier 3 when the input signal is bypassed.

(Third Embodiment) As shown in FIG. 3, the receiving circuit of the third embodiment includes a low noise amplifier control circuit, a low noise amplifier 3, and an output signal of the low noise amplifier 3. A gain control amplifier 31 that varies the gain according to the control voltage 34, a D / A converter 32 that converts the output data of the level determination circuit 24 from digital to analog, and a low-pass filter that filters the output voltage of the D / A converter 32. It is composed of a filter 33 and is configured to continuously vary the gain of the low noise amplifier control circuit,
Other configurations are the same as those in the first embodiment.

In this receiving circuit, the low noise amplifier control circuit is controlled by the level reference value I of the level judging circuit 24 as follows.

When the input level of the level determination circuit, that is, the interference wave level I input to the antenna 1 is I> I0, the output data of the level determination circuit 24 is DA-converted so that the interference wave level I becomes I0 or less. The control signal 34 generated by digital / analog conversion by the converter 32 and filtered by the low-pass filter 33 controls the gain of the gain control amplifier 31 in the direction of lowering it.

Next, when the input level of the level determination circuit, that is, the interfering wave level I input to the antenna 1 is I <I0, the level is determined so that the interfering wave level I becomes maximum within a range not exceeding I0. The output data of the circuit 24 is digital / analog converted by the DA converter 32, and a low-pass filter
The control signal 34 generated by filtering at 33 controls the gain control amplifier 31 in the direction of increasing the gain. As a result, by increasing the gain in the reception frequency band, the noise figure of the receiving circuit can be improved and the receiving sensitivity of the receiving circuit can be increased.

Therefore, the input level to the mixer 5 is controlled by varying the gain of the low noise amplifier control circuit according to the level of the interfering wave input to the antenna 1, and the intermodulation by the interfering wave input of two or more waves is performed. It is possible to minimize the deterioration of the reception characteristic due to, and to finely control the gain by continuously varying the gain by the gain control amplifier 31 as compared with the case where the level is controlled stepwise.

(Fourth Embodiment) As shown in FIG. 4, a receiver circuit according to a fourth embodiment of the present invention includes an antenna 1 for receiving a radio signal and a bandpass filter for filtering a signal received by the antenna 1. 2, a first switch 14 that switches the output of the bandpass filter 2 to two systems, a low noise amplifier 3 that amplifies one output of the first switch 14, an output of the low noise amplifier 3, and the first switch 14 Second switch 15 for switching the other output of the third switch, a third switch 16 for switching the load of the input of the low noise amplifier 3 and a fixed resistor 17, and a bandpass for filtering the output of the second switch 15. A filter 4, a mixer 5 that frequency-converts the output of the bandpass filter 4 with the output of the oscillator 6, a bandpass filter 7 that filters the output of the mixer 5, and a gain control amplifier that variably controls the output of the bandpass filter 7. If a quadrature detector 9 for quadrature detection output of the gain control amplifier 8, the output of the quadrature detector 9 I
A low-pass filter 10 and a low-pass filter 11 that filter the signal 12 and the Q signal 13, and an I signal 12 output from the quadrature detector 9.
High-pass filter 18 that filters the
Of the output of the AD converter 20, an integration circuit 23 that time-integrates the output of the AD converter 20, a multiplication circuit 35 that multiplies the output of the integration circuit 23 by a correction coefficient 36, and an output of the multiplication circuit 35. A level determination circuit 37 for comparison and determination is provided. The control signal 38 controls ON / OFF of the third switch 16 according to the level of the interfering wave detected by the integrating circuit 23, and the control signal 39 corresponds to that of the first switch 14 depending on the level of the interfering wave detected by the integrating circuit 23. The second switch 15 is on / off controlled.

Next, the operation of this receiving circuit will be described. First, the signal received by the antenna 1 is filtered by the bandpass filter 2, and the low noise composed of the first switch 14, the low noise amplifier 3, the second switch 15, the third switch 16 and the fixed resistor 17 is provided. The variable gain is controlled by the amplifier control circuit.
The operation of the low noise amplifier control circuit will be described later.

Next, the signal whose gain has been changed by the low noise amplifier control circuit is filtered by the bandpass filter 4 and mixed by the mixer 5 with the output signal of the oscillator 6 to be frequency-converted into an intermediate frequency band. The output signal of the mixer 5 converted into the intermediate frequency is filtered by the bandpass filter 7, amplified by the gain control amplifier 8 so that the output becomes constant, and then quadrature detected by the quadrature detector 9,
A signal 12 and a Q signal 13 are obtained.

The I signal 12 and the Q signal 13 are low-pass filters.
It is filtered by 10 and low-pass filter 11 and output. At the same time, the I signal 12 is filtered by the high-pass filter 18 and only the interfering wave component is extracted. The I signal 12 filtered by the high-pass filter 18 is subjected to analog / digital conversion by the AD converter 20 and time-integrated by the integrating circuit 23.

The I signal integrated by the integration circuit 23 is multiplied by the correction coefficient 36 by the multiplication circuit 35. By multiplying this correction coefficient, almost the same level detection result as that of detecting the level by the square root of the square sum of the I component and the Q component can be obtained. The output of the multiplication circuit 35 is compared with the reference level by the level determination circuit 37, and the level reference values I1 and I2 (I1 <I
By 2), the low noise amplifier control circuit is controlled as follows.

When the input level of the level judgment circuit 37, that is, the interference wave level I input to the antenna 1 is I <I1, the low noise amplifier control circuit controls the first switch 14 and the second switch 15 by the control signal 39. By the low noise amplifier 3 side,
The third switch 16 is opened by the control signal 38, and the input signal is amplified by the low noise amplifier 3 and output.

Next, the input level of the level judgment circuit 37, that is, the level I of the interference wave input to the antenna 1 is I1 <I.
In the case of <I2, the low-noise amplifier control circuit sets the first switch 14 and the second switch 15 to the low-noise amplifier 3 side by the control signal 39, and closes the third switch 16 by the control signal 38. The load of the fixed resistor 17 is added to the input of the noise amplifier 3, and the input signal of the low noise amplifier 3 is attenuated by the attenuation amount according to the resistance value of the fixed resistor 17, amplified by the low noise amplifier 3, and output.

Next, the input level of the level determination circuit 37, that is, the level I of the interference wave input to the antenna 1 is I> I2.
In the case of, the low noise amplifier control circuit is the first switch 1
4 and the second switch 15 are set to the bypass line side by the control signal 39, bypass the low noise amplifier 3, and are output.

Therefore, the input level to the mixer 5 is controlled by varying the gain of the low noise amplifier control circuit according to the level of the interfering wave input to the antenna 1, and the intermodulation by the interfering wave input of two or more waves is performed. It is possible to minimize the deterioration of the reception characteristic due to, and the level detection circuit of the first embodiment is simplified.

(Fifth Embodiment) As shown in FIG. 5, the receiving circuit of the fifth embodiment has a low noise amplifier control circuit for bypassing the low noise amplifier 3 and the low noise amplifier 3. No. 4 switch 28, a fifth switch 27 for turning on / off the power of the low noise amplifier 3, a third switch 16 for switching the input load of the low noise amplifier 3 and a fixed resistor 17, The circuit current of the noise amplifier is reduced, and the interfering wave level is detected only by the I signal output 12 of the quadrature detector 9 to simplify the circuit. Other configurations are the same as those in the fourth embodiment.

In this receiving circuit, the low noise amplifier control circuit is controlled by the level reference values I1 and I2 (I1 <I2) of the level determination circuit 37 as follows.

When the input level of the level determination circuit 37, that is, the interference wave level I input to the antenna 1 is I <I1, the low noise amplifier control circuit opens the fourth switch 28 by the control signal 42, The third switch 16 is opened by the control signal 40, the fifth switch 27 is closed, and the power source of the low noise amplifier 3 is turned on. At this time, the signal input to the low noise amplifier control circuit is amplified by the low noise amplifier 3 and output.

Next, the input level of the level judgment circuit 37, that is, the level I of the interference wave input to the antenna 1 is I1 <I.
In the case of <I2, the low noise amplifier control circuit causes the fourth switch 28 to be opened by the control signal 42, the fifth switch 27 to be closed, the power of the low noise amplifier 3 to be turned on, and the third switch 16 to be turned on. It is closed by the control signal 40, the load of the fixed resistor 17 is added to the input of the low noise amplifier 3, the input signal of the low noise amplifier 3 is attenuated by the attenuation amount according to the resistance value of the fixed resistor 17, and the low noise amplifier 3 Entered in
The low noise amplifier 3 amplifies and outputs.

Next, the input level of the level judgment circuit 37, that is, the interference wave level I input to the antenna 1 is I> I2.
If the low noise amplifier control circuit is the third switch 16
Is opened by the control signal 40, the input signal is closed by bypassing the fourth switch 28 by the control signal 42, the fifth switch 27 is opened by the control signal 29, and the low noise amplifier 3 is turned off. The effect of the low noise amplifier at the time of signal bypass is eliminated. At this time, the input signal is bypassed by the fourth switch 28 and output.

Therefore, the input level to the mixer 5 is controlled by varying the gain of the low noise amplifier control circuit according to the level of the interfering wave input to the antenna 1, and the intermodulation by the interfering wave input of two or more waves is performed. It is possible to minimize the deterioration of the reception characteristic due to, and to reduce the circuit current by turning off the power supply of the low noise amplifier 3 when the input signal is bypassed.

(Sixth Embodiment) As shown in FIG. 6, the receiver circuit of the sixth embodiment includes a low noise amplifier control circuit, a low noise amplifier 3, and an output signal of the low noise amplifier 3. A gain control amplifier 31 that varies the gain according to the control voltage 43, a D / A converter 32 that converts the output data of the level determination circuit 37 from digital to analog, and a low-pass filter that filters the output voltage of the D / A converter 32. The filter 33 is configured to continuously vary the gain of the low noise amplifier control circuit, and the interference wave level is detected only by the I signal output 12 of the quadrature detector 9, thereby simplifying the circuit. Other configurations are the same as those in the fourth embodiment.

In this receiving circuit, the low noise amplifier control circuit is controlled by the level reference value I of the level judging circuit 37 as follows.

When the input level of the level determining circuit 37, that is, the interfering wave level I input to the antenna 1 is I> I0, the output data of the level determining circuit 37 is set to DA so that the interfering wave level I becomes I0 or less. A converter 32 performs digital / analog conversion, and a control signal 43 generated by filtering with a low-pass filter 33 controls the gain of the gain control amplifier 31 in a direction of lowering it.

Next, the input level of the level judgment circuit 37, that is, the interference wave level I input to the antenna 1 is I <I0.
In the case of, the control generated by converting the output data of the level determination circuit 37 into digital / analog by the DA converter 32 and filtering by the low-pass filter 33 so that the interfering wave level I becomes maximum within a range not exceeding I0. Gain control amplifier with signal 43
It is controlled by increasing the gain of 31. As a result, by increasing the gain in the reception frequency band, the noise figure of the receiving circuit can be improved and the receiving sensitivity of the receiving circuit can be increased.

Therefore, the input level to the mixer 5 is controlled by varying the gain of the low noise amplifier control circuit according to the level of the interfering wave input to the antenna 1, and the intermodulation by the interfering wave input of two or more waves is performed. It is possible to minimize the deterioration of the reception characteristic due to, and to finely control the gain by continuously varying the gain by the gain control amplifier 31 as compared with the case where the level is controlled stepwise.

[0052]

As is apparent from the above description, the receiving circuit of the present invention detects the interfering wave level in the received signal and determines the gain of the receiving frequency band from the antenna to the mixer according to the interfering wave level. By variably controlling, it is possible to realize a receiver for digital mobile communication with less deterioration due to intermodulation interference.

[Brief description of drawings]

FIG. 1 is a circuit configuration diagram showing a receiver circuit according to a first embodiment of the present invention,

FIG. 2 is a circuit configuration diagram showing a receiving circuit according to a second embodiment of the present invention,

FIG. 3 is a circuit configuration diagram showing a receiving circuit according to a third embodiment of the present invention,

FIG. 4 is a circuit configuration diagram showing a receiver circuit according to a fourth embodiment of the present invention,

FIG. 5 is a circuit configuration diagram showing a receiving circuit according to a fifth embodiment of the present invention,

FIG. 6 is a circuit configuration diagram showing a receiving circuit according to a sixth embodiment of the present invention,

FIG. 7 is a circuit configuration diagram showing a conventional receiving circuit.

[Explanation of symbols]

 1 Antenna 2, 4, 7 Band Pass Filter 3 Low Noise Amplifier 5 Mixer 6 Oscillator 8 Gain Control Amplifier 9 Quadrature Detector 10, 11, 33 Low Pass Filter 12 I Signal 13 Q Signal 14 First Switch 15 Second Switch 16 Third switch 17 Fixed resistance 18,19 High-pass filter 20,21 AD converter 22 Level detection circuit 23 Integration circuit 24,37 Level judgment circuit 25,26,29,30,38 to 42 Control signal 27 Fifth switch 28 4th switch 31 Gain control amplifier 32 DA converter 34, 43 Control voltage 35 Multiplier circuit 36 Correction coefficient

Claims (6)

[Claims] 1. An antenna for receiving a radio signal, an amplifier for amplifying the received signal, a filter for filtering the received signal, a mixer for frequency-converting the received signal to an intermediate frequency band, and a signal for the intermediate frequency band. In a receiving circuit having an amplifier for amplifying, a filter for filtering a signal in an intermediate frequency band, and a quadrature detector for quadrature detecting a signal in the intermediate frequency band,
A high-pass filter for filtering the output I signal and the output Q signal of the quadrature detector, and the output I of the high-pass filter
A for analog / digital conversion of signal and output Q signal
A D converter, a level detection circuit for performing level detection from the output of the AD converter, an integration circuit for time-integrating the output of the level detection circuit, and a level determination circuit for comparing the output of the integration circuit with a reference value. And a low noise amplifier gain control circuit that varies the gain in the reception frequency band according to the output data of the level determination circuit, wherein the low noise amplifier gain control circuit branches the reception signal of the antenna into two.
Switch, a low noise amplifier for amplifying the branched signal, a second switch for switching the output of the low noise amplifier and the output signal of the first switch, and a load for switching the input of the low noise amplifier. 3. A receiving circuit comprising a switch of No. 3 and a fixed resistor, and on / off controlling each of the switches by a control signal of the level determining circuit to variably control the gain. 2. A low-noise amplifier gain control circuit that bypasses the low-noise amplifier and the low-noise amplifier.
Of the low-noise amplifier, a fifth switch for turning on / off the power supply of the low-noise amplifier, the third switch for switching the load of the input of the low-noise amplifier, and the fixed resistor. The receiving circuit according to claim 1, wherein each switch is on / off controlled by a control signal to variably control the gain. 3. The low noise amplifier gain control circuit digitally outputs the low noise amplifier, a gain control amplifier for varying the gain of an output signal of the low noise amplifier according to a control voltage, and output data of the level determination circuit. / D / A converter for analog / analog conversion and a low-pass filter for filtering the output voltage of the D / A converter. The control signal of the level determination circuit is digital / analog converted by the D / A converter. The receiving circuit according to claim 1, wherein the gain of the gain control amplifier is controlled by the control voltage filtered by the low-pass filter, and the gain is variably controlled. 4. An antenna for receiving a radio signal, an amplifier for amplifying the received signal, a filter for filtering the received signal, a mixer for frequency-converting the received signal into an intermediate frequency band, and a signal for the intermediate frequency band. In a receiving circuit having an amplifier for amplifying, a filter for filtering a signal in an intermediate frequency band, and a quadrature detector for quadrature detecting a signal in the intermediate frequency band,
A high-pass filter that filters the output signal of the quadrature detector, an AD converter that performs analog / digital conversion of the output I signal of the high-pass filter, an integrating circuit that time-integrates the output of the AD converter, and an integrating circuit of the integrating circuit. A level determination circuit that compares the output and a reference value, and a low noise amplifier gain control circuit that varies the gain of the reception frequency band according to the output data of the level determination circuit, the low noise amplifier gain control circuit, A first switch for branching the received signal of the antenna into two; a low noise amplifier for amplifying the branched signal; a second switch for switching the output of the low noise amplifier and the output signal of the first switch; It is composed of a third switch for switching the input load of the low noise amplifier and a fixed resistor, and each switch is turned on by a control signal of the level judgment circuit. / Off control, the receiving circuit, characterized by variably controlling the gain. 5. A fourth low noise amplifier gain control circuit for bypassing the low noise amplifier and the low noise amplifier.
Of the low-noise amplifier, a fifth switch for turning on / off the power supply of the low-noise amplifier, the third switch for switching the load of the input of the low-noise amplifier, and the fixed resistor. 5. The receiving circuit according to claim 4, wherein each switch is on / off controlled by a control signal to variably control the gain. 6. The low noise amplifier gain control circuit digitally outputs the output data of the low noise amplifier, a gain control amplifier for varying the gain of an output signal of the low noise amplifier according to a control voltage, and output data of the level determination circuit. / D / A converter for analog / analog conversion and a low-pass filter for filtering the output voltage of the D / A converter. The control signal of the level determination circuit is digital / analog converted by the D / A converter. The receiving circuit according to claim 4, wherein the gain of the gain control amplifier is controlled by the control voltage filtered by the low-pass filter, and the gain is variably controlled.