JP2001016056A - Semiconductor integrated circuit and am receiver - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a semiconductor integrated circuit and AM receiver which are free of deterioration in reception sensitivity and deterioration in disturbance characteristics, when an active filter is used as a band-pass filter. SOLUTION: An AM wave received by an antenna 1 is amplified by a high- frequency amplifier 2. The amplified signal is converted by a frequency conversion part 3 into an intermediate-frequency signal. This intermediate-frequency signal is amplified by a variable gain amplifier 6 and the active filter 7 limits its band. An audio signal is extracted from the band-limited signal by an AM detector 8. At this time, the level of the signal inputted to the active filter 7 is adjusted by a detection sensitivity adjusting circuit 11. An analog OR circuit 12 compares the signal inputted to the AM detector 8 and the signal adjusted by the detection sensitivity adjusting circuit 11 with each other and outputs a larger signal. According to the output signal of the analog OR circuit 12, an automatic gain control circuit 14 controls the gain of the variable gain amplifier 6.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a semiconductor integrated circuit and an AM receiver, and more particularly to a semiconductor integrated circuit and an AM receiver for receiving an AM wave using an active filter as a bandpass filter.

[0002]

2. Description of the Related Art A configuration example of a conventional AM receiver will be described below.

FIG. 5 is a circuit diagram showing a configuration of a conventional AM receiver. First, an AM signal wave is received by an antenna 101 and amplified by a high frequency (RF) amplifier 102. The amplified AM signal wave is converted to an intermediate frequency signal (IF signal) by the frequency converter 103 and output to the intermediate frequency end 106. The frequency conversion unit 103 includes a voltage controlled oscillator (VCO) 104 and a frequency mixer 105.

The intermediate frequency signal output to the intermediate frequency end 106 is band-limited by a ceramic filter 107,
Input to the intermediate frequency stage 108. Ceramic filter 1
Reference numeral 07 denotes a band pass filter, which has a role of selecting a desired reception wave. The intermediate frequency stage 108 includes a variable gain amplifier 109 capable of changing the gain, an automatic gain control (AGC) circuit 110 for controlling the gain, and an A for performing detection.
It comprises an M detector 111. This intermediate frequency stage 108
Extracts an audio signal from the input intermediate frequency signal and outputs the audio signal to an output terminal 113.

The automatic gain control (AGC) circuit 110
Receives a signal input to the input unit of the AM detector 111 from the node 112 (AGC detection unit), and controls the gain of the variable gain amplifier 109 according to the magnitude of the signal. This allows the intermediate frequency stage 108 to
The level of the audio signal to be output is kept constant by keeping the magnitude of the signal input to the AM detector 111 irrespective of the magnitude of the signal 6.

[0006]

In the AM receiver shown in FIG. 5, a ceramic filter is used as a band-pass filter. Since the ceramic filter is externally attached to the IC, a space for the substrate is required, and the cost increases accordingly. Therefore, it is advantageous to replace the ceramic filter with an active filter that can be built into an IC.

FIG. 6 is a block diagram showing a configuration in which the ceramic filter 107 in FIG. 5 is replaced with an active filter 114 having a built-in IC. When the active filter 114 with a built-in IC is used as described above, the substrate space is not required, and the cost can be reduced accordingly.

However, in the configuration shown in FIG. 6, the noise output from the active filter 114 increases the noise level, which causes a decrease in sensitivity. FIG. 7 shows the received signal characteristics (the relationship between the audio output level and the input electric field strength). An audio output level (signal level (S)) 32 with AM modulation, an audio output level (noise level (N)) 33 without AM modulation,
S / N is defined by a ratio of 34. Then, the sensitivity becomes the prescribed S / N (A in the figure) when the electric field is weak, and the electric field strength 35, 3
6 (practical sensitivity).

In the configuration shown in FIG. 5, the ceramic filter 107 does not emit noise because it is a passive element. Therefore, the noise level (N) in this case is 33, and the sensitivity is 35. However, in the case of the configuration shown in FIG. 6, the active filter 114 emits noise internally. Therefore, at the time of a weak electric field in which the signal level passing through the active filter 114 becomes small, the passing signal is buried in the noise, and the noise level (N) becomes 34, and the sensitivity deteriorates to 36.

The present invention has been made in view of the above-mentioned problems, and an object of the present invention is to provide a semiconductor integrated circuit and an AM receiver which do not cause a decrease in reception sensitivity and a deterioration in interference characteristics when an active filter is used as a bandpass filter. The purpose is to provide.

[0011]

In order to achieve the above object, a semiconductor integrated circuit according to the present invention is provided with a variable gain amplifying means capable of amplifying an input signal and varying an amplification factor thereof, and the variable gain amplifying means. An active filter for band-limiting the signal amplified by the means, a detector for extracting an output signal from a signal passed through the active filter, and a detection sensitivity for detecting a signal input to the active filter and adjusting the magnitude of the signal Adjusting means, a signal input to the detection means, a signal adjusted by the detection sensitivity adjusting means, a comparing means for outputting a signal having a higher level, and a signal output from the comparing means. Automatic gain control means for outputting a control signal for adjusting the gain of the variable gain amplifying means.

Further, a semiconductor integrated circuit according to the present invention is
A first variable gain amplifying unit capable of amplifying an input signal and making the amplification factor variable, a first active filter for band-limiting the signal amplified by the first variable gain amplifying unit, A second variable gain amplifying means for amplifying a signal passing through the active filter and making the gain variable, a second active filter for band-limiting the signal amplified by the second variable gain amplifying means, Detection means for extracting an output signal from a signal passed through the second active filter; detection sensitivity adjustment means for detecting a signal input to the first active filter and adjusting the magnitude of the signal; Input signal and
A comparing unit that compares the signal adjusted by the detection sensitivity adjusting unit and outputs a signal having a higher level; and a gain of the first and second variable gain amplifying units according to an output of the comparing unit. And automatic gain control means for respectively outputting control signals for adjusting the gain.

Also, the AM receiver according to the present invention provides an AM receiver
Receiving means for receiving a wave, amplifying means for amplifying the output signal of the receiving means, frequency converting means for converting the frequency of the output signal of the amplifying means, and amplifying the output signal of the frequency converting means, Variable gain amplifying means capable of changing the gain, an active filter for band-limiting the output signal of the variable gain amplifying means, detecting means for extracting an audio signal from the output signal of the active filter, and input to the active filter A detection sensitivity adjustment unit that detects a signal and adjusts the magnitude of the signal; a signal input to the detection unit and a signal adjusted by the detection sensitivity adjustment unit; And an automatic gain control for outputting a control signal for adjusting the gain of the variable gain amplifying means according to the output signal of the comparing means. Characterized by comprising a means.

Also, the AM receiver according to the present invention provides an AM receiver
Receiving means for receiving a wave, amplifying means for amplifying the output signal of the receiving means, frequency converting means for converting the frequency of the output signal of the amplifying means, and amplifying the output signal of the frequency converting means, 1st variable gain
Variable gain amplifying means, and a first active filter for band-limiting an output signal of the first variable gain amplifying means,
A second variable gain amplifying means for amplifying an output signal of the first active filter and making the gain variable, and a second active filter for band limiting the output signal of the second variable gain amplifying means Detection means for extracting an audio signal from the output signal of the second active filter; detection sensitivity adjustment means for detecting a signal input to the first active filter and adjusting the magnitude of the signal; A comparison unit that compares a signal input to the detection unit with a signal adjusted by the detection sensitivity adjustment unit and outputs a signal of a higher level; and the first unit according to an output signal of the comparison unit. And an automatic gain control means for outputting a control signal for adjusting the gain of the second variable gain amplifying means.

[0015]

Embodiments of the present invention will be described below with reference to the drawings.

[First Embodiment] FIG. 1 is a circuit diagram showing a configuration of an AM receiver according to a first embodiment of the present invention.

An antenna 1 for receiving an AM signal wave is a radio frequency (RF) for selecting and amplifying a signal in a desired frequency band.
It is connected to the frequency converter 3 via the amplifier 2. The frequency converter 3 includes a voltage controlled oscillator (VCO) 4 and a frequency mixer 5. The frequency converter 3 converts the signal amplified by the high frequency (RF) amplifier 2 into an intermediate frequency signal (IF signal). The output unit of the frequency conversion unit 3 is
It is connected via a variable gain amplifier 6 to an active filter 7 that limits the band. The output of the active filter 7 is connected to an AM detector 8 that performs detection. An output terminal 9 is provided at an output section of the AM detector 8.

A detection sensitivity adjusting circuit 11 is connected to a connection point (node 10) between the variable gain amplifier 6 and the active filter 7. The output of the detection sensitivity adjustment circuit 11 is connected to the first terminal of the analog OR circuit 12. A second terminal of the analog OR circuit 12 is connected to a connection point (node 13) between the active filter 7 and the AM detector 8. The output of the analog OR circuit 12 is connected to an automatic gain control (AGC) circuit 14, and the output of the automatic gain control circuit 14 is connected to the variable gain amplifier 6 capable of changing the gain. A connection point between the frequency converter 3 and the variable gain amplifier 6 is defined as an intermediate frequency end 15.

Next, the operation of the AM receiver thus configured will be described.

First, an AM signal wave is received by an antenna 1 and input to a high frequency amplifier 2. This high frequency amplifier 2
Then, a signal in a desired frequency band is selected from the AM signal wave, amplified, and input to the frequency conversion unit 3. The signal input to the frequency converter 3 is converted into an intermediate frequency signal (IF signal) by the frequency converter
5 is output.

The intermediate frequency signal output to the intermediate frequency terminal 15 is amplified by the variable gain amplifier 6 and further band-limited by the active filter 7. Due to this band limitation, only the desired wave is input to the AM detector 8. And
An audio signal is extracted from the desired wave by the AM detector 8 and output to an output terminal 9.

Here, the signal detected from the node 10 (AGC detecting section) provided at the input section of the active filter 7 has its magnitude adjusted by the detection sensitivity adjusting circuit 11, and the signal is detected by the analog OR circuit 12. Input to one terminal.
The node 1 provided at the input of the AM detector 8
3 (AGC detection unit) detects the analog OR
The signal is input to the second terminal of the circuit 12. Analog OR circuit 1
2, the signal inputted to the first terminal and the signal inputted to the second terminal are compared, and the larger signal is selected and the automatic gain control circuit 14
Is output to The automatic gain control circuit 14 outputs a control signal for adjusting the gain of the variable gain amplifier 6 according to the input signal. The variable gain amplifier 6 receives a control signal, sets a gain according to the control signal, and amplifies the input intermediate frequency signal.

That is, the signal detected from the node 13 provided at the input of the AM detector 8 and the signal detected from the node 10 provided at the input of the active filter 7 are adjusted by the detection sensitivity adjusting circuit 11. The larger signal is selected by the analog OR circuit 12 from the signals thus obtained. Then, the gain of the variable gain amplifier 6 is adjusted by the AGC circuit 14 according to the magnitude of the selected signal. In this way, by controlling the gain of the variable gain amplifier 6 and keeping the magnitude of the signal input to the AM detector 8 constant irrespective of the magnitude of the intermediate frequency signal, the audio signal is kept constant. ing.

In the AM receiver according to the first embodiment,
The configuration from the antenna 1 for receiving the AM signal wave to the intermediate frequency end 15 for outputting the intermediate frequency signal is the same as that of the conventional example shown in FIG. This is a method of performing frequency conversion only once. Therefore, the band of the signal that appears at the intermediate frequency end 15 as the intermediate frequency signal is a band adjusted at a desired reception frequency of the high frequency amplifier 2 and the frequency conversion unit 3
Is the band to be converted.

In the first embodiment, the intermediate frequency signal is amplified by the variable gain amplifier 6 and then input to the narrow band active filter 7. When only the desired wave is input to the variable gain amplifier 6 as the intermediate frequency signal, the following is performed. The desired wave amplified by the variable gain amplifier 6 is
The signal passes through the active filter 7, is detected from a node 13 (AGC detector) provided at the input of the AM detector 8, and is input to the second terminal of the analog OR circuit 12.
Then, according to the signal input to the second terminal of the analog OR circuit 12, the analog OR circuit 12 and the AGC circuit 1
4, the gain of the variable gain amplifier 6 is adjusted. In the variable gain amplifier 6, when the electric field strength of the desired wave is large, the gain is changed to be small, and when the electric field strength is small, the gain is changed greatly, so that the gain depends on the electric field strength of the intermediate frequency signal input to the variable gain amplifier 6. Instead, the magnitude of the signal passing through the active filter 7 is made constant.

Therefore, even when the electric field strength of the intermediate frequency signal is weak, the electric field strength of the signal passing through the active filter 7 increases, and the signal is not buried in the internal noise of the active filter. Thus, it is possible to prevent the receiving sensitivity (practical sensitivity) from deteriorating at the time of a weak electric field. However, in this case, it is necessary to adjust the detection sensitivity adjustment circuit 11 so that the analog OR circuit 12 selects a signal from the node 13 which is an input unit of the AM detector 8.

On the other hand, when an interfering wave other than the desired wave is simultaneously input to the variable gain amplifier 6 as an intermediate frequency signal, the following operation is performed. The desired wave and the interference wave are simultaneously amplified by the variable gain amplifier 6 and input to the active filter 7. The active filter 7 allows the desired wave to pass therethrough but blocks the interfering wave.
, Only the desired wave is detected. When the gain of the variable gain amplifier 6 is controlled by the magnitude of the detection signal, when the magnitude of the interfering wave is larger than the desired wave, the interfering wave exceeds the dynamic range of the active filter 7 and the intermediate frequency The signal collapses, and thus the desired wave collapses, disturbing the audio output.

Therefore, in this embodiment, detection is also performed from the node 10 which is the input part of the active filter 7,
The gain of the variable gain amplifier 6 is adjusted so that the output signal of the variable gain amplifier 6 does not exceed the dynamic range of the active filter 7. Thus, when an interference wave other than the desired wave simultaneously enters, it is possible to prevent the desired wave from being disturbed and the interference characteristics from being deteriorated.

Next, a specific configuration example of the detection sensitivity adjustment circuit 11 and the analog OR circuit 12 in the AM receiver shown in FIG. 1 will be described.

FIG. 2 is a circuit diagram showing a specific configuration of the detection sensitivity adjustment circuit 11 and the analog OR circuit 12.

A signal detected from a node 13 which is an input of the AM detector 8 is transmitted to an automatic gain control (AGC) circuit 14 through a transistor TR1. A signal detected from a node 10 which is an input portion of the active filter 7 is transmitted to an AGC circuit 14 through a transistor TR2 after a voltage level is adjusted by a detection sensitivity adjustment circuit 11 including a resistor R2 and a resistor R3. Can be At this time, resistance division is performed by the resistors R2 and R3, and the voltage level of the signal detected from the node 10 is reduced.

Since the transistors TR1 and TR2 have their emitters connected in common, they operate as analog OR circuits that trace the higher voltage of the signal applied to each base and transmit it to the AGC circuit 14.
The AGC circuit 14 has a configuration for detecting the height of the input voltage value.

The operation of adjusting the gain of the variable gain amplifier 6 using the detection signal from the node 13 is to keep the input level to the AM detector 8 constant so that the output (detection output) of the audio signal is constant. Has the role of doing. The operation of adjusting the gain of the variable gain amplifier 6 using the detection signal from the node 10 is performed so that the input level to the active filter 7 is suppressed to be smaller than a predetermined value so that the dynamic range of the active filter 7 is not exceeded. Has the role of doing.

When only the desired wave is input to the active filter 7, assuming that the gain of the active filter 7 is 0 dB, the voltage levels of the signals detected from the nodes 10 and 13 are the same. However, node 10
Since the resistor R2 is provided between the transistor TR2 and the transistor TR2, the signal applied to the base of the transistor TR1 is larger than the signal applied to the base of the transistor TR2. Therefore, the detection signal from the node 13 becomes valid, and an operation for keeping the detection output constant is performed.

On the other hand, when a desired wave and an interfering wave are simultaneously input to the active filter 7, if the interference wave exceeds the dynamic range of the active filter 7 by the operation of keeping the detection output of the desired wave constant, , The signal detected from node 10 becomes larger than the signal detected from node 13, ie, the signal applied to the base of transistor TR2 is
Larger than the signal applied to the base of Therefore, the detection signal from the node 10 becomes valid, and an operation is performed so as not to exceed the dynamic range of the active filter 7.

In the AM receiver configured as described above,
By using an active filter that can be incorporated in an IC, it is not necessary to provide a ceramic filter outside the IC, and the substrate area and cost can be reduced. Further, by amplifying the received signal by the variable gain amplifier and then inputting the amplified signal to the active filter, it is possible to prevent the sensitivity from being deteriorated due to the use of the active filter. Furthermore, the input signal to the AM detector and the input signal to the active filter are compared after adjusting the latter voltage level, and the gain of the variable gain amplifier is controlled using the larger signal. Accordingly, it is possible to prevent the interference performance from deteriorating without changing the reception signal characteristics.

As described above, according to the first embodiment, when the external ceramic filter used as the band-pass filter is replaced with the active filter having the built-in IC, the reception sensitivity is reduced and the interference characteristic is reduced. A semiconductor integrated circuit for reception and an AM receiver that can prevent deterioration can be realized. Further, the ceramic filter external to the IC can be replaced with an active filter built in the IC, which is advantageous in terms of substrate area and cost.

[Second Embodiment] Next, an AM receiver according to a second embodiment of the present invention will be described.

FIG. 3 shows a second embodiment of the present invention.
FIG. 3 is a circuit diagram illustrating a configuration of an M receiver.

In the second embodiment, the frequency conversion from the antenna 1 to the intermediate frequency end 15 is performed twice. The steps from the intermediate frequency end 15 to the output terminal 9 are the same as in the first embodiment.

The antenna 1 for receiving the AM signal wave is connected to a frequency converter 21 via a radio frequency (RF) amplifier 20 for selecting and amplifying a signal of a desired frequency. The frequency converter 21 includes a voltage controlled oscillator (VCO) 22,
It comprises a first frequency mixer 23, a first intermediate frequency ceramic filter 24, an oscillator (OSC) 25, and a second frequency mixer 26. The frequency converter 21 converts the signal amplified by the high frequency amplifier 20 into a second intermediate frequency signal (2nd IF signal). The configuration from the intermediate frequency end 15 provided on the output unit of the frequency conversion unit 21 to the output terminal 9 is the same as that of the first embodiment shown in FIG.

Next, the operation of the AM receiver thus configured will be described.

First, the AM signal wave is received by the antenna 1 and input to the high frequency amplifier 20. The AM signal wave is amplified by the high frequency amplifier 20 and input to the frequency conversion unit 21. The signal input to the frequency converter 21 is converted to a second intermediate frequency signal by the frequency converter 21 and output to the intermediate frequency terminal 15.

In this case, the band of the signal output to the intermediate frequency terminal 15 is determined mainly by the first intermediate frequency ceramic filter 24, and the signal in that band is input to the variable gain amplifier 6. The band of the ceramic filter 24 is wide enough to obtain the selectivity with the adjacent station, and the intermediate frequency end 1
Audio signals are output from 5 to the output terminal 9 by the same operation as in the first embodiment.

As described above, according to the second embodiment, when the external ceramic filter used as the band-pass filter is replaced by the active filter having the built-in IC, the reception sensitivity is reduced and the interference characteristic is reduced. A semiconductor integrated circuit for reception and an AM receiver that can prevent deterioration can be realized.

[Third Embodiment] Next, an AM receiver according to a third embodiment of the present invention will be described.

FIG. 3 shows a third embodiment of the present invention.
FIG. 3 is a circuit diagram illustrating a configuration of an M receiver.

In the third embodiment, the variable gain amplifier has two stages in order to increase the amount of automatic gain control (AGC). At this time, since the active filter has a multi-stage configuration of higher order to realize a narrow band, the variable gain amplifier and the active filter are alternately arranged. Antenna 1 to intermediate frequency end 15
The configuration up to this point is the same as that of the first embodiment.

An antenna 1 for receiving an AM signal wave is a radio frequency (RF) for selecting and amplifying a signal in a desired frequency band.
It is connected to the frequency converter 3 via the amplifier 2. The frequency converter 3 includes a voltage controlled oscillator (VCO) 4 and a frequency mixer 5. The frequency converter 3 converts the signal amplified by the high frequency (RF) amplifier 2 into an intermediate frequency signal (IF signal).

The output of the frequency converter 3 is connected to the first active filter 31 for limiting the band via the intermediate frequency terminal 15 and the first variable gain amplifier 30. The output of the first active filter 31 is connected via a second variable gain amplifier 32 to a second active filter 33 that limits the band. The output of the second active filter 33 is connected to the AM detector 8 that performs detection. An output terminal 9 is provided at an output section of the AM detector 8.

At the connection point (node 34) between the first variable gain amplifier 30 and the first active filter 31,
The detection sensitivity adjustment circuit 35 is connected. An output section of the detection sensitivity adjustment circuit 35 is connected to a first terminal of the analog OR circuit 36. A second terminal of the analog OR circuit 36 is connected to a connection point (node 37) between the second active filter 33 and the AM detector 8. Analog OR circuit 36
Is connected to an automatic gain control (AGC) circuit 38. The output of the automatic gain control circuit 38 is connected to the first variable gain amplifier 30 and the second variable gain amplifier 32 capable of changing the gain. .

Next, the operation of the AM receiver thus configured will be described.

First, the AM signal wave is received by the antenna 1 and input to the high frequency amplifier 2. This high frequency amplifier 2
Then, a signal in a desired frequency band is selected from the AM signal wave, amplified, and input to the frequency conversion unit 3. The signal input to the frequency converter 3 is converted into an intermediate frequency signal (IF signal) by the frequency converter
5 is output.

The intermediate frequency signal output to the intermediate frequency terminal 15 is amplified by a first variable gain amplifier 30 and band-limited by a first active filter 31. Subsequently, the signal that has passed through the first active filter 31 is amplified by a second variable gain amplifier 32 and band-limited by a second active filter 33. Due to this band limitation, only the desired wave is input to the AM detector 8. An audio signal is extracted from the desired wave by the AM detector 8 and output to an output terminal 9.

Here, the first active filter 3
The signal detected from the node 34 (AGC detection unit) provided at the input unit 1 has its magnitude adjusted by the detection sensitivity adjustment circuit 35 and is input to the first terminal of the analog OR circuit 36. Further, a signal detected from a node 37 (AGC detector) provided at an input section of the AM detector 8 is input to a second terminal of the analog OR circuit 36. Analog O
In the R circuit 36, the signals input to the first terminal and the second terminal are compared, and the larger signal is selected and output to the automatic gain control circuit 38. The automatic gain control circuit 38 controls the first variable gain amplifier 30 and the second variable gain amplifier 30 in accordance with the input signal.
The control signal for adjusting the gain of the variable gain amplifier 32 is output. The first and second variable gain amplifiers 30 and 32 receive the control signal, set the gain according to the control signal, and amplify the input intermediate frequency signal.

That is, the signal detected from the node 37 provided at the input of the AM detector 8 and the signal detected from the node 34 provided at the input of the first active filter 31 are detected by the detection sensitivity adjustment circuit 35. The larger signal is selected by the analog OR circuit 36 from the adjusted signals. Then, the first and second variable gain amplifiers 30 and 3 are operated by the AGC circuit 38 in accordance with the magnitude of the selected signal.
The gain of 2 is adjusted. In this way, by controlling the gains of the variable gain amplifiers 30 and 32 and keeping the magnitude of the signal input to the AM detector 8 constant irrespective of the magnitude of the intermediate frequency signal, the audio signal is It is constant. Here, the configuration from the antenna 1 to the intermediate frequency end 15 is the same as that of the first embodiment,
The embodiment may be similar to that of the embodiment.

In the AM receiver configured as described above,
By using an active filter that can be incorporated in an IC, it is not necessary to provide a ceramic filter outside the IC, and the substrate area and cost can be reduced. Further, by amplifying the received signal by the variable gain amplifier and then inputting the amplified signal to the active filter, it is possible to prevent the sensitivity from being deteriorated due to the use of the active filter. Furthermore, the input signal to the AM detector and the input signal to the active filter are compared after adjusting the latter voltage level, and the gain of the variable gain amplifier is controlled using the larger signal. Accordingly, it is possible to prevent the interference performance from deteriorating without changing the reception signal characteristics.

By using two stages of variable gain amplifiers, the amount of automatic gain control (AGC) can be increased. This increases the freedom of setting from the antenna to the frequency conversion unit, and facilitates optimal design. Further, by dividing the active filter into two stages, a required narrow band filter can be easily configured.

As described above, according to the third embodiment, when a ceramic filter external to an IC used as a band-pass filter is replaced by an active filter built in the IC, the reception sensitivity is reduced and the interference characteristic is reduced. A semiconductor integrated circuit for reception and an AM receiver that can prevent deterioration can be realized. Further, the ceramic filter external to the IC can be replaced with an active filter built in the IC, which is advantageous in terms of substrate area and cost.

[0060]

As described above, according to the present invention, there is provided a semiconductor integrated circuit and an AM receiver which do not cause a decrease in reception sensitivity and a deterioration in interference characteristics when an active filter is used as a bandpass filter. Can be.

[Brief description of the drawings]

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

FIG. 2 is a circuit diagram showing a specific configuration of a detection sensitivity adjustment circuit and an analog OR circuit in the AM receiver.

FIG. 3 is a circuit diagram showing a configuration of an AM receiver according to a second embodiment of the present invention.

FIG. 4 is a circuit diagram showing a configuration of an AM receiver according to a third embodiment of the present invention.

FIG. 5 is a circuit diagram illustrating a configuration example of a conventional AM receiver.

FIG. 6 is a circuit diagram showing another configuration example of the AM receiver.

FIG. 7 is a diagram showing received signal characteristics (relationship between audio output level and input electric field strength).

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Antenna 2 ... High frequency (RF) amplifier 3 ... Frequency converter 4 ... Voltage controlled oscillator (VCO) 5 ... Frequency mixer 6 ... Variable gain amplifier 7 ... Active filter 8 ... AM detector 9 ... Output terminal 10 ... Node 11 ... Detection sensitivity adjustment circuit 12 ... Analog OR circuit 13 ... Node 14 ... Automatic gain control (AGC) circuit 15 ... Intermediate frequency end E ... Bias voltage I1 ... Constant current source R1, R2, R3 ... Resistance TR1, TR2 ... Transistor Vcc ... Power supply voltage 20 ... High frequency (RF) amplifier 21 ... Frequency converter 22 ... Voltage controlled oscillator (VCO) 23 ... First frequency mixer 24 ... Ceramic filter for first intermediate frequency 25 ... Oscillator (OSC) 26 ... 2 frequency mixer 30 ... first variable gain amplifier 31 ... first active filter 32 ... second variable gain amplifier 33 The second active filter 34 ... node 35 ... detection sensitivity adjustment circuit 36 ... analog OR circuit 37 ... node 38 ... automatic gain control (AGC) circuit

Claims (8)

[Claims] 1. A variable gain amplifying means capable of amplifying an input signal and varying an amplification factor thereof, an active filter for limiting a band of a signal amplified by the variable gain amplifying means, and an output from a signal passed through the active filter. Detection means for extracting a signal; detection sensitivity adjustment means for detecting a signal input to the active filter and adjusting the magnitude of the signal; and a signal input to the detection means and adjustment by the detection sensitivity adjustment means. Comparison means for comparing the obtained signal with a higher level signal, and automatic gain control means for outputting a control signal for adjusting the gain of the variable gain amplifying means according to the output of the comparison means. A semiconductor integrated circuit, comprising: 2. A first variable gain amplifying means capable of amplifying an input signal and making the gain variable, and a first active filter for limiting a band of the signal amplified by the first variable gain amplifying means. A second variable gain amplifying means capable of amplifying a signal passing through the first active filter and making the gain variable, and a second band limiting a signal amplified by the second variable gain amplifying means. An active filter; a detection unit that extracts an output signal from a signal passed through the second active filter; a detection sensitivity adjustment unit that detects a signal input to the first active filter and adjusts the magnitude of the signal. A comparison unit that compares a signal input to the detection unit with a signal adjusted by the detection sensitivity adjustment unit and outputs a signal having a higher level; Automatic gain control means for outputting control signals for adjusting the gains of the first and second variable gain amplifying means in accordance with the output of the means. A receiving means for receiving an AM wave; an amplifying means for amplifying an output signal of the receiving means; a frequency converting means for converting a frequency of an output signal of the amplifying means; and an output signal of the frequency converting means. Variable gain amplifying means capable of amplifying the gain and making the gain variable, an active filter for band-limiting an output signal of the variable gain amplifying means, a detecting means for extracting an audio signal from an output signal of the active filter, A detection sensitivity adjustment unit that detects a signal input to the active filter and adjusts the magnitude of the signal; a signal input to the detection unit and a signal adjusted by the detection sensitivity adjustment unit; Comparing means for outputting a signal having a higher level, and a control signal for adjusting the gain of the variable gain amplifying means according to the output signal of the comparing means. AM receiver characterized by comprising an automatic gain control means, the outputs of. A receiving means for receiving an AM wave; an amplifying means for amplifying an output signal of the receiving means; a frequency converting means for converting a frequency of an output signal of the amplifying means; and an output signal of the frequency converting means. Variable gain amplifying means capable of amplifying the gain and making the gain variable, a first active filter for band limiting an output signal of the first variable gain amplifying means, and a first active filter. A second variable gain amplifying unit capable of amplifying an output signal and making the amplification factor variable; a second active filter for band-limiting an output signal of the second variable gain amplifying unit; Detection means for extracting an audio signal from the output signal of the filter; detection sensitivity for detecting a signal input to the first active filter and adjusting the magnitude of the signal Adjusting means, comparing the signal input to the detection means, the signal adjusted by the detection sensitivity adjusting means, and outputting a signal of a larger level, and according to the output signal of the comparing means Automatic gain control means for outputting control signals for adjusting the gains of the first and second variable gain amplifying means, respectively. 5. The active filter is incorporated in the same IC as the variable gain amplifying means, the detecting means, the detection sensitivity adjusting means, the comparing means, and the automatic gain control means. The AM receiver according to claim 3 or 4. 6. The AM receiver according to claim 3, wherein said amplification means is a high-frequency amplifier for selecting and amplifying a signal of a desired frequency band from said AM wave. Machine. 7. The AM receiver according to claim 6, wherein said frequency conversion means is means for converting a signal amplified by said high-frequency amplifier into an intermediate frequency signal. 8. The AM receiver according to claim 1, wherein said comparing means is an analog OR circuit.