JP2774776B2 - Receiving machine - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a superheterodyne receiver suitably implemented as an on-vehicle radio receiver, and more particularly, to a receiver for performing an AGC operation for preventing distortion at a strong input. About the machine.

[0002]

2. Description of the Related Art FIG. 5 is a block diagram showing the electrical configuration of a typical prior art radio receiver 1. Antenna 2
In the tuning signal 3, only the signal component in the vicinity of the frequency of the desired wave to be received is emphasized, and the received signal is amplified by the high-frequency amplifier 4 and then input to the mixing circuit 5. In connection with this mixing circuit 5, a local oscillation circuit 6
Is provided. The local oscillation circuit 6 is realized by a voltage-controlled oscillator or the like, and includes a phase locked loop (hereinafter, referred to as a phase locked loop).
A local oscillation signal having a frequency corresponding to the tuning voltage from the circuit 7 is output.

The PLL circuit 7 includes a frequency divider for dividing the local oscillation signal at a frequency division ratio N corresponding to the frequency of the desired wave input from a control circuit 8 realized by a microcomputer or the like. A reference signal source for generating a reference signal having a predetermined reference frequency, a comparator for comparing the phase of the reference signal with the frequency-divided local oscillation signal and generating an error output corresponding to the difference, and the comparator And a filter that smoothes the error output from the local oscillation circuit into a DC voltage and supplies the DC voltage to the local oscillation circuit 6 and the tuning circuit 3 as the tuning voltage. Therefore, when changing the reception frequency, the control circuit 8 changes the N value, and adjusts the tuning voltage so that the phase difference between the signal obtained by dividing the local oscillation signal by the N value and the reference signal becomes zero. Is changed, and thus stable reception of a desired wave becomes possible.

[0004] The mixing circuit 5 mixes the local oscillation signal obtained as described above with the received signal, and the obtained intermediate frequency signal can filter only a component containing a voice signal. The signal is supplied to the intermediate frequency amplifier circuit 10 via the narrow band filter 9. The filtering bandwidth of the narrow band filter 9 is, for example, 1 when receiving frequency modulation broadcast.
It is selected to be about 80 kHz.

The intermediate frequency signal amplified by the intermediate frequency amplifier circuit 10 is applied to a detection circuit 11 and demodulated into an audio signal. The demodulated audio signal is applied to a power amplifier 13 and amplified. Is given to the speaker 14 to be acousticized.

The output from the high-frequency amplifier circuit 4 is
The signal is input to a first level detection circuit 15, and the level detection circuit 15 outputs a first AGC voltage corresponding to a reception level near a frequency of a desired wave amplified by the tuning circuit 3 and the high-frequency amplification circuit 4. This is provided to the adder 16. The adder 16 is also provided with a second level detection circuit 17.
The reception signal level is detected from the intermediate frequency signal level or the demodulated audio signal level in the detection circuit 11, and the detection result is input as the second AGC voltage.
The output from the adder 16 is provided to an attenuator circuit 18.

The attenuator circuit 18 is provided in association with the tuning circuit 3, and increases as the output voltage from the adder 16 increases, that is, the first and second AGs.
As the C voltage increases, the resonance sharpness of the tuning circuit 3 decreases. As a result, when the antenna input level is high, the resonance sharpness of the tuning circuit 3 decreases, and the signal level input to the high-frequency amplifier circuit 4 is suppressed as compared with the case where the antenna input level is low. Thus, the AGC operation is performed in a stage preceding the high-frequency amplifier circuit 4 and the mixing circuit 5 whose distortion characteristics are deteriorated by a strong input.

[0008]

In the prior art as described above, the second AGC voltage has a level corresponding to the received signal level of only the desired wave filtered by the narrow band filter 9. Therefore, when the AGC operation is performed only with the second AGC voltage, the influence of the interference wave of the frequency adjacent to the frequency of the desired wave is not considered at all, and the interference wave causes distortion in the high-frequency amplifier circuit 4 and the mixing circuit 5. Would.

On the other hand, the first AGC voltage is affected by the interference wave, and the desired wave may be undesirably suppressed because the reception level of the interference wave is large. If the AGC operation is performed only with the first AGC voltage, the AGC operation is performed even if the level of the desired wave is strong, and the SN characteristic deteriorates.

On the other hand, the transistor circuit forming the mixing circuit 5 has such a characteristic that the larger the bias current is, the more the dynamic range is shifted to the strong input side, and the distortion for the strong input is reduced. However, the dynamic range of this transistor circuit is constant. Therefore, if the bias current is increased to make the transistor circuit resistant to distortion, when the signal level of the desired wave is small, the dynamic range deviates from the dynamic range. Thus, there arises a problem that a small signal cannot be handled.

An object of the present invention is to provide a receiver capable of reliably listening to a desired wave.

[0012]

According to the present invention, there is provided an attenuator element for attenuating and controlling the gain of a tuning circuit, and the attenuation level of the attenuator element is controlled by a first level detection circuit according to the reception level in the high frequency amplifier circuit. Is changed in accordance with the first AGC voltage output from the second AGC voltage and the second AGC voltage output from the second level detection circuit in accordance with the level of the received signal in the detection circuit so as to suppress distortion for a strong input. And a mixing circuit capable of changing an appropriate input level in response to a change in a bias current, and adding the first and second AGC voltages to output to the attenuator element. An adder, and when an output of the adder is equal to or higher than a predetermined level, a first AGC voltage is used as the bias current. A receiver which comprises a bias switching means for providing the focus circuit. The present invention also provides
In response to the second AGC voltage, tone control means is provided for attenuating a high-frequency component of the demodulated audio signal as the received signal level decreases, and the bias switching means comprises: If it is above, the first
Is combined with the second AGC voltage, and the first AGC voltage
The tone control means attenuates high-frequency components as the C voltage increases.

[0013]

According to the present invention, an attenuator element for attenuating and controlling the gain of the tuning circuit is provided, and the attenuation level of the attenuator element is determined based on the output of the high-frequency amplifier circuit.
Represents the reception level output from the level detection circuit of FIG.
And the second AGC voltage representing the level of the intermediate frequency signal in the detection circuit or the level of the received signal output from the second level detection circuit based on the level of the demodulated audio signal from the detection circuit. In the receiver of the superheterodyne system which suppresses distortion in a mixing circuit or the like for a strong input, the first and second AGC voltages are added by an adding means and applied to the attenuator element. When the output of the adding means is equal to or higher than a predetermined level, the bias switching means supplies the first AGC voltage as a bias current to a transistor circuit constituting the mixing circuit in a mixing circuit.

Therefore, the first A including the influence of the interference wave
A wide band AGC operation using a GC voltage, and a narrow band AGC using a second AGC voltage indicating a desired signal reception signal level
When the operation is performed and the level of the interfering wave is increased and becomes equal to or higher than the predetermined level, the bias current of the mixing circuit is increased to be more resistant to a distortion with respect to a strong input. Is less than the predetermined level, the bias current is not increased as described above, and the appropriate input level of the mixing circuit is set relatively small, so that a small signal can be reliably heard.

Preferably, the demodulated audio signal line includes:
In response to the second AGC voltage, there is provided tone control means for attenuating a high-frequency component of the demodulated audio signal as the received signal level decreases, and the bias switching means outputs the output of the adding means. When the level is equal to or higher than a predetermined level, the first AGC voltage is combined with the second AGC voltage and supplied to the tone control means.

Therefore, the tone control means is provided with the second A
The higher the level suppression amount corresponding to the GC voltage, the higher the frequency component is attenuated, and the higher the bias current of the mixing circuit is, the stronger the influence of the interfering wave is. Further, high frequency components are attenuated. Thus, it is possible to suppress the influence of noise and make it easier to hear the desired wave.

[0017]

FIG. 1 shows a radio receiver 2 according to an embodiment of the present invention.
FIG. 2 is a block diagram showing an electrical configuration of FIG. Antenna 22
In the received signal received by the tuning circuit 23, only the signal component near the frequency of the desired wave to be received is emphasized in the tuning circuit 23,
After being amplified by the high frequency amplifier circuit 24, the mixed circuit 2
5 is input. In connection with the mixing circuit 25, a local oscillation circuit 26 is provided. The local oscillation circuit 26
Is realized by a voltage controlled oscillator or the like, and the PLL circuit 27
And outputs a local oscillation signal having a frequency corresponding to the tuning voltage from.

The PLL circuit 27 includes a frequency divider for dividing the local oscillation signal by a frequency division ratio N corresponding to the frequency of the desired wave input from a control circuit 28 implemented by a microcomputer or the like. A reference signal source for generating a reference signal having a predetermined reference frequency, a comparator for comparing the phase of the reference signal with the frequency-divided local oscillation signal and generating an error output corresponding to the difference, and the comparator And a filter for smoothing an error output from the local oscillation circuit to a DC voltage and applying the smoothed voltage to the local oscillation circuit 26 and the tuning circuit 23 as the tuning voltage. Therefore, when changing the reception frequency, the control circuit 28 changes the N value, and adjusts the tuning voltage so that the phase difference between the signal obtained by dividing the local oscillation signal by the N value and the reference signal becomes zero. Is changed, and thus stable reception of a desired wave becomes possible.

The mixing circuit 25 mixes the local oscillation signal obtained as described above with the received signal, and the obtained intermediate frequency signal can filter only a component including a voice signal. The signal is supplied to the intermediate frequency amplifier circuit 30 via the narrow band filter 29. The filtering bandwidth of the narrow-band filter 29 is selected to be, for example, about 180 kHz when receiving frequency-modulated broadcasting.

The intermediate frequency signal amplified by the intermediate frequency amplifying circuit 30 is applied to a detection circuit 31 to demodulate an audio signal.
After being supplied to the power amplifier 33 via the amplifier and amplified, the signal is supplied to the speaker 34 to be acousticized.

The output from the high frequency amplification circuit 24 is also input to a first level detection circuit 41. The first level detection circuit 41 outputs the frequency of the desired wave amplified by the tuning circuit 23 and the high frequency amplification circuit 24. When a nearby reception level is detected and the detected level is equal to or higher than the predetermined level V1, a DC voltage corresponding to the level is output to the adder 42 as a first AGC voltage as indicated by reference numeral α1 in FIG. I do.

A second level detection circuit 43 is provided in connection with the detection circuit 31. The second level detection circuit 43 converts the level of the intermediate frequency signal or the level of the demodulated audio signal in the detection circuit 31 into the level of the received signal. And the detection result is supplied to the non-inverting input terminal of the comparator 44. The inverting input terminal of the comparator 44 has a reference voltage source 4
5, a predetermined reference voltage Vref1 is input.

Therefore, the input to the detection circuit 31 is the high-frequency amplification circuit 2 which is the input to the level detection circuit 41.
4, the gain is high because the intermediate frequency amplifying circuit 30 is interposed, so that the comparator 44 outputs
As shown by reference numeral α2 in FIG. 2, a DC voltage of a level corresponding to the received signal level is output until the antenna input level changes from a level V2 smaller than the level V1 to a level V3 corresponding to the reference voltage Vref1. And for an antenna input above level V3,
An output whose output is clipped to the constant voltage E1 is derived.

The voltage E1 is selected as an AGC voltage that can be generated in a state where the reception state is the best, that is, when the reception is performed in the vicinity of the transmitting station without multipath. Accordingly, in the first AGC voltage from the level detection circuit 41 indicated by the reference numeral α1, the section indicated by the reference numeral α1a indicates a case where there is an interference wave having a frequency adjacent to the frequency of the desired wave.

The output from the comparator 44 is supplied to the second AG
The C voltage is given to the adder 42. The first and second AGC voltages synthesized by the adder 42 are supplied to an attenuator circuit 35 provided to attenuate and control the gain of the tuning circuit 23.

The attenuator circuit 35 reduces the resonance sharpness of the tuning circuit 23 as the AGC voltage increases as described later. Therefore, when the received electric field strength level at the antenna 22 is high, the resonance sharpness of the tuning circuit 23 is reduced, and the signal level input to the high frequency amplifier circuit 24 is suppressed as compared with the case where the received electric field strength level is low. Will be. Thus, the AGC operation for preventing the occurrence of distortion in the high-frequency amplifier circuit 24, the mixing circuit 25, and the like at the subsequent stage is realized.

The tuning circuit 23 comprises a
And a tuning unit 37 on the side of the detection circuit 31 at the subsequent stage. Matching unit 36
Are provided for matching between the antenna 22 and the tuning circuit 23, and are coupled in series with a line 38 connected to the high-frequency amplifier circuit 24.
2 and a matching capacitor C interposed between a connection point between these coupling capacitors C1 and C2 and a ground line.
3 is provided.

On the other hand, the tuning section 37 is connected to the line 38
Inductor L1 and variable capacitance diode D1, which are interposed between
D2 and a coupling capacitor C interposed in the line 38.
4 and a damping resistor R1 for the tuning voltage. Variable capacitance diodes D1, D2
Are connected in series with each other so that they have opposite polarities, and are interposed between the line 38 and a ground line, and the connection point between them is supplied with the tuning voltage via a damping resistor R1. . Therefore, for example, the variable capacitance diode D1
When the capacitance of the variable capacitance diode D2 increases, the capacitance of the variable capacitance diode D2 also increases, thereby tuning to the reception signal of the frequency to be received and emphasizing and outputting the signal.

The attenuator circuit 35 smoothes an AGC voltage from the adder 42 and a series circuit of a capacitor C5 and a diode D3 connected to a connection point 36a between the matching section 36 and the tuning section 37. A resistor R2 and a capacitor C6 which constitute an integrating circuit for outputting a signal; and a diode D4 for preventing a reverse current which applies the AGC voltage to a connection point between the capacitor C5 and the diode D3.
It is comprised including. When the AGC voltage smoothed by the capacitor C6 becomes equal to or higher than the conduction voltage of the diode D3, the diode D3 conducts, and the capacitor C5 is connected in parallel with the matching capacitor C3. , The level suppression operation is performed by lowering the resonance sharpness.

Further, in the present invention, in performing the above-mentioned AGC operation, a comparator 47 for comparing the AGC voltage from the adder 42 with a reference voltage Vref2 from a reference voltage source 46, and a comparator 47 A bias switching circuit 50 including a switch 48 that is opened and closed by an output.
Is provided. In the bias switching circuit 50, when the AGC voltage becomes equal to or higher than the reference voltage Vref2, the switch 48 is turned on and the first detection signal from the level detection circuit 41 is output.
Is supplied to the mixing circuit 25 as a bias current. Note that the bias switching circuit 50 may be a bias variable circuit that continuously varies a bias current.

The mixing circuit 25 is implemented by including a transistor circuit and the like, and mixes a reception signal from the high-frequency amplification circuit 24 with a local oscillation signal from a local oscillation circuit 26; The current
And a bias current source that performs adjustment control in accordance with the first AGC voltage.

Therefore, when the switch 48 is turned off, that is, when the level of the interfering signal is relatively small, the value of the bias current of the mixing circuit 25 is reduced, and the dynamic range of the mixing circuit 25, that is, the appropriate input Even if the level is set to the low level side and the desired wave is a weak input, the desired wave can be heard. On the other hand, when the level of the interfering signal that causes the switch 48 to conduct is large, the bias current is increased, and the dynamic range of the mixing circuit 25 is shifted to a high level, so that the distortion is suppressed even for a strong input. Is less likely to occur.

According to the present invention, the first AGC voltage via the switch 48 is added to the second AGC voltage from the level detection circuit 43 in the adder 49,
It is provided to tone control circuit 32. Tone control circuit 32
Is configured to include, for example, a low-pass filter (abbreviated LPF), an adder, and two multipliers, and converts the audio signal from the detection circuit 31 into a component passing through the LPF and a component passing through the bypass line. After the components are separated and the ratio of those components is adjusted by the multiplier coefficient corresponding to the AGC voltage in the multiplier, the components are added and output by the adder.

Therefore, when the second AGC voltage is low, the input audio signal is output as it is via the bypass line, and as the second AGC voltage increases, the ratio of the signal component via the LPF increases. As the high-frequency component is further suppressed and the first AGC voltage is further added, the high-frequency component is further suppressed. Thus, when the first AGC voltage is applied to the mixing circuit 25 as a bias current at a strong input,
In FIG. 3, the output audio signal level and the output noise signal level with respect to the antenna input level in the normal state as indicated by reference signs β1 and β2
Even when the noise is noticeable due to the increase as indicated by β2a, the noise can be made less noticeable by attenuating the high frequency components.

The radio receiver 21 configured as described above
In FIG. 2, as the weak input changes to the strong input,
As indicated by reference numeral α2, the second AGC voltage increases from the input level V2 to V3, and above the level V3, the second AGC voltage is clipped to the voltage E1. When the input level becomes the level V1 higher than the level V3, the level detection circuit 41
A first AGC voltage as shown in FIG.

Therefore, the AG added by the adder 42
The frequency characteristics of the C voltage are as shown in FIG. As is apparent from FIG. 4, a component near the frequency fo of the desired wave that can pass through the narrow band filter 29 is suppressed by the voltage E1 due to a synergistic effect with the second AGC voltage. On the other hand, as for the interference wave component, the AGC operation using the second AGC voltage is not performed, and a high AGC voltage is output.

On the other hand, in FIG.
As indicated by ref2, the reference voltage of the reference voltage source 46 of the comparator 47 is set, and therefore A
When the GC voltage becomes equal to or higher than the reference voltage Vref2, the switch 48 is turned on and the bias current is increased.

Therefore, at the time of a weak input, the bias current of the mixing circuit 25 is small, so that even if the desired wave is a weak input, it is possible to listen. On the other hand, when the component of the interference wave is equal to or higher than the level corresponding to the reference voltage Vref2, the bias current control is performed,
The dynamic range of the mixing circuit 25 is set to the strong input side,
After the bias current of the mixing circuit 25 reaches the maximum value, the AGC operation is performed by the first AGC voltage.
If the disturbing signal is large, the level is suppressed by the first AGC voltage to suppress the occurrence of distortion, and the mixing circuit 25
The noise component is suppressed by the tone control circuit 32 to make the desired wave component less noticeable due to the deterioration of the noise characteristic due to the increase in the bias current in the mixing circuit 25. It becomes possible.

The present invention is not limited to radio receivers for frequency-modulated broadcasting, but can be applied to other receivers of the superheterodyne system such as radio receivers for amplitude-modulated broadcasting and receivers for television broadcasting.

[0040]

As described above, according to the present invention, an attenuator element for attenuating and controlling the gain of the tuning circuit is provided, and the attenuation level of the attenuator element is set to the first AGC voltage corresponding to the output of the high-frequency amplifier circuit. And a second AGC voltage corresponding to an intermediate frequency signal level in a detection circuit or a demodulated audio signal level from the detection circuit, thereby performing level suppression for a strong input. , The first and second AGs
When the addition result of the C voltage is equal to or higher than a predetermined level, the first AGC voltage is applied as a bias current to a transistor circuit or the like constituting the mixing circuit in the mixing circuit. The bias current of the circuit is increased to increase the distortion against strong input. On the other hand, when the input is weak, the bias current is not increased as described above, and the appropriate input level of the mixing circuit is set to a relatively small value. Thus, a small signal can be reliably heard.

Preferably, the demodulated audio signal line
In response to the second AGC voltage, there is provided tone control means for attenuating the high frequency component of the demodulated audio signal as the received signal level decreases, and when the input is strong, the first AGC voltage is reduced to the second AGC voltage. Since the signal is synthesized with the voltage and applied to the tone control means, the higher-frequency component is attenuated as the level suppression amount increases in accordance with the second AGC voltage, and the higher-frequency component is further attenuated as the influence of the interfering wave becomes stronger. , The desired wave can be easily heard.

[Brief description of the drawings]

FIG. 1 is a block diagram showing an electrical configuration of a radio receiver 21 according to one embodiment of the present invention.

FIG. 2 is a graph illustrating an AGC operation of the radio receiver 21.

FIG. 3 is a graph illustrating a change in input / output characteristics due to an increase in a bias current of a mixing circuit 25 of the radio receiver 21;

FIG. 4 is a graph showing a frequency characteristic of the AGC voltage.

FIG. 5 is a block diagram showing an electrical configuration of a typical conventional radio receiver 1;

[Explanation of symbols]

 Reference Signs List 21 radio receiver 23 tuning circuit 24 high frequency amplifier circuit 25 mixing circuit 26 local oscillation circuit 27 PLL circuit 28 control circuit 29 narrow band filter 30 intermediate frequency amplifier circuit 31 detection circuit 32 tone control circuit 35 attenuator circuit 41, 43 level detection circuit 44 , 47 Comparator 50 Bias switching circuit

Claims (2)

(57) [Claims] An attenuator element for attenuating the gain of a tuning circuit is provided, and an attenuation level of the attenuator element is output from a first level detection circuit according to a reception level in a high-frequency amplifier circuit. A superheterodyne receiver in which the voltage is changed according to the voltage and the second AGC voltage output from the second level detection circuit in accordance with the level of the received signal in the detection circuit to suppress distortion for a strong input. A mixing circuit capable of changing an appropriate input level in response to a change in a bias current; an adding means for adding the first and second AGC voltages to output to the attenuator element; When the output is equal to or higher than a predetermined level, a bias for applying the first AGC voltage to the mixing circuit as the bias current is provided. A receiver comprising switching means. 2. A tone control means for attenuating a high-frequency component of a demodulated audio signal as the received signal level decreases in response to the second AGC voltage; When the output is equal to or higher than a predetermined level, the first AGC voltage is combined with the second AGC voltage, and the tone control means attenuates the high frequency component as the first AGC voltage increases. The receiver according to claim 1.