JPH05259778A - Automatic gain controller - Google Patents

Abstract

PURPOSE:To attenuate an excess signal just after signal input in the automatic gain controller. CONSTITUTION:Reproduction signals 21, 22 from a CD or the like are processed by a stereo modulation section 25 and a composite signal 26 is inputted to an FM modulation section 27. A composite signal 26 is subject to peak hold by a peak hold circuit 30 and attenuators 34, 35 are operated by a gain control voltage 33 with a fast leading and the reproduction signals 21, 22 are immediately suppressed. Overmodulation by the FM modulation section 27 just after the signal input is prevented by eliminating a delay in the leading of the gain control voltage 33.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention is provided, for example, in a modulation output device that FM-modulates a reproduction output of a CD player and outputs it to an FM radio tuner. For example, an input signal to an FM modulator is adjusted according to its intensity. The present invention relates to an automatic gain control device that suppresses the above.

[0002]

2. Description of the Related Art FIG. 6 is a circuit block diagram showing a modulation output device which FM-modulates a reproduction output of a vehicle-mounted CD player and outputs it to an FM radio tuner of a vehicle-mounted radio.
In this modulation output device 1, the reproduction output 2 of L / R read from the in-vehicle CD player is sent to the stereo modulation unit 3, and this stereo modulation unit 3 reproduces the reproduction output 2 (L +
A composite signal 4 including a main signal modulated by the (R) signal, a sub signal modulated by the (LR) signal, and a pilot signal of 19 kHz is generated. The FM modulator 5 uses the composite signal 4 to output, for example, 88.5.
The carrier wave of MHz is FM-modulated, and this is output to the FM radio tuner 7 of the in-vehicle radio via the switching unit 6, and F
The reproduced sound demodulated by the M radio tuner 7 is output from the speaker.

The switching unit 6 can switch between the FM modulation output from the FM modulation unit 5 of the output device 1 and the input from the antenna 8 provided in the automobile, and the radio reception is performed. Sometimes the input from the antenna 8 is sent to the FM radio tuner 7, and when the reproduction from the CD is performed, the output from the modulation output device 1 is sent to the FM radio tuner 7.

Here, there is a difference in dynamic range (width between standard modulation and maximum modulation) between the reception function of the FM radio tuner 7 manufactured for the purpose of receiving FM broadcasting and the stereo modulation of the reproduction output of the CD. There is a problem that has occurred. That is, in the case of receiving a broadcast wave by FM modulation, the dynamic range is about 10 dB, whereas the CD
The dynamic range of the modulation output in the stereo modulator 3 for obtaining the reproduction output of the player is about 20 dB. Therefore, when the composite signal 4 from the stereo modulator 3 is FM-modulated by the FM modulator 5 as it is and sent to the FM radio tuner 7, the FM radio tuner 7 receives the overmodulated FM signal, and the reproduced sound is reproduced. Distortion is likely to occur. In particular, the stereo modulation unit 3 is provided with a pre-emphasis function for raising the high frequency range. Therefore, when overmodulation occurs due to this high frequency signal, the FM radio tuner 7
Distortion is likely to occur in the high sound of the reproduced sound demodulated by.

Therefore, recently, as shown in FIG. 6, the composite signal 4 output from the stereo modulator 3 is detected by the gain control circuit 9, and the gain control voltage 11 output from the gain control circuit 9 causes It is considered that the attenuator 10, which is an input control unit, operates to suppress the reproduction output 2 to the stereo modulation unit 3 and prevent overmodulation by the FM modulation unit 5.

[0006]

However, the automatic gain control device using the gain control circuit 9 as shown in FIG. 6 has the following problems. In the gain control circuit 9,
The rectifier circuit of the diodes D1 and D2 rectifies the composite signal 4 by half-wave voltage and smoothes it by a low-pass filter having a large time constant by the resistor R and the capacitor C to generate a DC gain control voltage 11. This controls the attenuator 10 using a transistor or the like, and the intensity of the input signal to the stereo modulation unit 3 and further the FM modulation unit 5
The strength of the input signal to is suppressed.

FIG. 7 (A) shows the waveform of the composite signal 4 input to the FM modulator 5 from the stereo modulator 3 shown in FIG. 6, and FIG. 7 (B) shows the gain control from the gain control circuit 9. The change of the voltage value of the voltage 11 is shown. As shown in each diagram of FIG. 7, when the reproduction of the CD is started, the composite signal 4 from the stereo modulator 3 is detected, and the gain control circuit 9 outputs the gain control voltage 11 in accordance with the intensity of the composite signal 4. The attenuator 10 reduces the amplification gain of the reproduction output 2 to suppress the composite signal 4 and
It is sent to the modulator 5. However, in the gain control circuit 9 shown in FIG. 6, the DC signal (gain control voltage 11) is generated by smoothing the composite signal 4 by the low-pass filter of the RC circuit having a large time constant, so that the time constant of RC is large. As a result, the rise of the gain control voltage 11 is dull, and a certain long rise time t occurs until the composite signal 4 is suppressed. The FM modulation output of the overmodulation is given from the FM modulator 5 to the FM radio tuner 7 for the time t, and the reproduced sound from the speaker, particularly the high frequency range, is distorted during the time t.

The present invention has been made to solve the above-mentioned conventional problems, and it is possible to prevent the input signal from becoming excessively large immediately after the signal is input, and to prevent overmodulation or the like at the time of signal input. An object is to provide an automatic gain control device.

[0009]

According to the present invention, there is provided a gain control section for detecting the strength of an input signal and outputting a gain control power, and an input control section for changing the strength of the input signal according to the gain control power. In the automatic gain control device provided with, the gain control section is constituted by a peak hold circuit as a first means, and the gain control section is suppressed by the input control section as a second means. An amplitude limiting circuit for limiting the amplitude of the signal is provided. As a third means, the input signal is pre-emphasis processed, and the input signal is passed through a high pass filter to obtain the gain control section. It is characterized by being input to.

[0010]

In the first means, the peak hold circuit is used as the gain control unit. However, in the case of the peak hold circuit, the gain control power output from the gain control unit rises quickly, so that the signal immediately after the input is input. Even when the intensity of is high, the gain control power rises quickly, and proper suppression can be applied immediately after signal input.

In the second means, even if the gain control voltage rises slowly, the signal strength at the start of input is limited by the amplitude limiting circuit. Therefore, the strength of the signal immediately after input is temporarily excessive. Therefore, it is possible to prevent overmodulation.

In the third means, in the case of the pre-emphasis processed signal, only the high frequency modulation component is input to the gain control section through the high pass filter, and the gain control power is based on the high frequency modulation component. Is generated and the strength of the input signal is suppressed. Therefore, the gain control is performed only when the intensity of the high frequency component becomes high due to the pre-emphasis. For example, when FM modulation is performed by an input signal, sound distortion and the like become remarkable when the high frequency band is overmodulated. Therefore, by performing gain control only by the high frequency component, it is possible to prevent sound distortion and the like due to overmodulation. become able to.

[0013]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a circuit block diagram of a modulation output device that FM-modulates a reproduction output of a vehicle-mounted CD player and outputs it to an FM radio tuner of a vehicle-mounted radio as an example of a device using the automatic gain control device according to the present invention. In this modulation output device 20, an L-channel reproduction signal 21 and an R-channel reproduction signal 22 read from a vehicle-mounted CD player (not shown) and a pre-emphasis circuit 23 composed of resistors and capacitors, respectively. It is input to the stereo modulation unit 25 via 24. The pre-emphasis circuit 23
And 24 can be switched to the "normal reproduction mode" or "treble enhanced reproduction mode" by switching the resistance value, for example. In the stereo modulator 25, a main signal (L + R) modulated by the (L + R) signal based on the L channel reproduction signal 21 and the R channel reproduction signal 22,
-R) sub-signal modulated by signal, and 19 kHz
And a pilot signal of the composite signal 26 is generated. In the FM modulation unit 27, a carrier of 88.5 MHz, for example, is FM-modulated by the composite signal 26, and this is output to the FM radio tuner 7 of the vehicle-mounted radio via the switching unit 6, demodulated by the FM radio tuner 7 and the speaker. The reproduced sound is output from.

The switching unit 6 is capable of switching between the FM modulation output from the modulation output device 20 and the input from the antenna 8 provided in the automobile. When receiving radio, the switching unit 6 outputs from the antenna 8. When the input is sent to the FM radio tuner 7 and the CD is played back,
The output from the modulation output device 20 is sent to the FM radio tuner 7. In the modulation output device 20 shown in FIG. 1, a peak hold circuit 30 is used as a gain control unit, and this and an attenuator 34, 35 which is an input control unit constitute an automatic gain control device.

The composite signal 26 output from the stereo modulator 25 and input to the FM modulator 27 is detected at the detection point 2
8 is detected, the voltage is amplified by the amplifier 29, and the voltage is sent to the peak hold circuit 30. The peak hold circuit 30 includes operational amplifiers 31 and 32, a peak detection diode Da, and a smoothing circuit including a resistor Ra and a capacitance Ca. The DC voltage smoothed by the smoothing circuit of Ra and Ca is impedance-converted by the voltage loop of the operational amplifier 32, and the low impedance DC voltage is negatively fed back to the inverting input section of the operational amplifier 31. Therefore, the AC composite signal 26 detected at the detection point 28 has its peak value sampled by the operational amplifier 31, the peak signal detected by the diode Da, and smoothed by the smoothing circuit of Ra and Ca. Therefore, the gain control voltage 33 obtained from the peak hold circuit 30 becomes the peak hold voltage.

Here, in the peak hold circuit 30,
Since the DC voltage converted into low impedance by the operational amplifier 32 is negatively fed back to the operational amplifier 32, Ra
And the input impedance to Ca is low. Further, the rise time of peak detection (Δt in FIG. 4 (B)) can be shortened by the time constant of the internal resistance Rb and the capacitance Ca in the operational amplifier 31, the followability to the increase of the composite signal 26 can be improved, and Ra and Ca By increasing the time constant, the recovery time shown in FIG. 4B, that is, the discharge time T from the capacity Ca can be lengthened. Therefore, it is possible to set the recovery time (discharge time) T to be long so that the gain control voltage 33 does not drop sharply and to eliminate a feeling of strangeness in hearing.

At the next stage of the peak hold circuit 30, an attenuator 34 for the L channel and an attenuator 35 for the R channel are provided. The gain control voltage 33 output from the peak hold circuit 30 is given to the transistor Ta of the attenuator 34 as a base voltage,
Similarly, the gain control voltage 33 is applied to the transistor Tb of the attenuator 35 as a base voltage. The transistor T of each attenuator 34, 35
The collectors of a and Tb are coupled to the input portions of the reproduced signals 21 and 22 of the L channel and the R channel, respectively, and have coupling capacitances Cb and C, respectively.
It is connected via b.

When the peak hold circuit 30 obtains a peak voltage corresponding to the fluctuation of the composite signal 26 as the gain control voltage 33, the gain control voltage 33 is obtained.
The current is applied to the bases of the transistors Ta and Tb of the transistor 35, and a current flows between the collector and the emitter in accordance with the base voltage to attenuate the reproduction signals 21 and 22 of the L channel and the R channel, respectively, and suppress the composite signal 26. Thus, the FM modulator 27 is prevented from overmodulating.

FIG. 4A shows the level change of the composite signal 26 immediately after the CD reproduction signals 21 and 22 are started to be input in the embodiment shown in FIG. 1, and FIG.
Indicates the voltage change of the gain control voltage 33 at this time. In the peak hold circuit 30 shown in FIG.
Since the rising edge of the peak detection can be set quickly by the capacitance Ca and the capacitance Ca, the reproduction signals 21 and 2 are input to the stereo modulator 25.
2 is input, and when the output intensity of the composite signal 26 instantaneously increases due to the dynamic range of the stereo modulation unit 25, the gain control voltage 33 from the peak hold circuit 30 can be raised in a very short time Δt. .. Therefore, the reproduced signal 2 is generated by the attenuators 34 and 35.
1 and 22 are immediately suppressed and composite signal 26 is instantaneously attenuated.

That is, compared with the conventional example shown in FIG. 7A, the attenuators 34 and 35 provide input signals 21 and 22.
Since it is attenuated in a short time, even if overmodulation occurs in the FM modulator 27, this becomes an extremely short time indicated by Δt, and the distortion of the reproduced sound demodulated by the FM radio tuner immediately after the reproduction is It hardly happens. Moreover, as shown in FIG. 4B, the resistance Ra and the capacitance C are
Since the recovery time (discharge time) T can be set longer by using a, it is possible to eliminate a feeling of strangeness in hearing.

FIG. 2 is a circuit block diagram showing a second embodiment of the present invention. In this embodiment, as the gain control section 41, either the peak hold circuit 30 used in the embodiment of FIG. 1 or the conventional gain control circuit 9 shown in FIG. 6 is used. And the stereo modulator 2
A limiter (amplitude limiting circuit) 42 is provided at the subsequent stage of the detection point 28 in the output section of the composite signal 26 from 5.

FIG. 5A shows a limiter 42 in FIG.
Reproduction signals 21 and 22 when no
Shows the strength change of the composite signal 26 immediately after the input of
FIG. 5C shows the change in the intensity of the output 26a passing through the limiter 42 when the limiter 42 is provided.
Further, FIG. 5B shows the gain control voltage 33 given from the gain control unit 41 to the attenuators 34 and 35 based on the intensity of the composite signal 26 detected from the detection point 28.

In FIG. 5A, the allowable input range φ is
The allowable range of the intensity of the FM modulation signal with respect to the FM radio tuner 7 is shown, and this shows the range in which overmodulation does not occur according to the dynamic range of the FM radio tuner 7. Also, the limiter range φ0 in FIG.
The amplitude limit range by the limiter 42 is shown. This limiter range φ0 is narrower than the input allowable range φ, and the intensity range φ1 when the attenuators 34 and 35 are operated by the gain control voltage 33 and the composite signal 26 is attenuated.
A wider range, that is, the composite signal 26 can be prevented from being overmodulated, and the strength of the gain-controlled composite signal 26 is not affected.

As shown in FIG. 5 (A), in this embodiment, when the intensity of the composite signal 26 immediately after the reproduction signals 21 and 22 from the CD are input is instantaneously increased, the intensity range thereof is increased. Is limited by the limiter 42.
In FIG. 5C, the time during which the limiter 42 limits the amplitude is indicated by t1. At the same time, the gain control unit 4
The gain control voltage 33 from 1 attenuators 34, 3
When 5 operates and the composite signal 26 begins to be suppressed, the intensity of the composite signal 26 falls within the limiter range φ0 and is sent to the FM modulator 27 without being subjected to amplitude limitation by the limiter 42.

In the second embodiment, the limiter 42 having the limiter range φ0 as shown in FIG. 5C is provided to limit the strength of the composite signal immediately after the reproduction signals 21 and 22 are input. Since the FM modulator 27 prevents overmodulation, distortion of the acoustic output immediately after reproduction can be prevented when demodulated by the FM radio tuner 7. Further, in this embodiment, the reproduction signal 21
Since the amplitude can be limited by the limiter 42 at the time of rising of the control signals 22 and 22, regardless of the time constant of the RC circuit in the gain control section 41, that is, regardless of the length of the rising time t1 of the gain control voltage 33, the FM modulation section 27 It is possible to prevent overmodulation.

Next, a third embodiment of the present invention will be described with reference to FIG. In this embodiment, a peak hold circuit 30 is used as a gain control section as in FIG. The difference from the embodiment shown in FIG. 1 is that a high-pass filter 45 is provided in the preceding stage of the peak hold circuit 30.
Further, in the attenuators 34a and 35a as the input control section, the high frequency attenuator is configured so that only the high frequency components are attenuated with respect to the reproduced signals 21 and 22 by the capacitance values of the coupling capacitors Cd and Cd.

In the third embodiment, the reproduction signals 21 and 22 are reproduced.
Even when the strength of the composite signal 26 becomes high at the rising edge of, the high frequency signal passes through the high pass filter 45 and the peak hold circuit only when the composite signal 26 at this time includes a high frequency component of a certain frequency or higher. It is input to 30. Then, the peak-held gain control voltage 33 is obtained, and the high frequency attenuators 34a, 35 are
As a operates, only the high frequency component of a certain frequency or more of the reproduced signals 21 and 22 is suppressed. When the intensity of the high frequency component included in the composite signal 26 becomes a certain value or less, the suppression does not work for the entire frequencies of the reproduction signals 21 and 22.

In the embodiment shown in FIG. 3, the stereo modulator 25 is used.
Has a pre-emphasis function. When the high frequency is emphasized by the pre-emphasis and the strength of this high frequency signal becomes high, the high frequency attenuator 34
The high frequency components of the reproduced signals 21 and 22 are suppressed by a and 35a. However, the reproduced signals 21 and 2
Even when the level of the entire composite signal 26 becomes high as immediately after the input of 2, the attenuators 34a and 35a suppress the input when the composite signal 26 does not include high frequency components. If this is not done, the overmodulated FM modulation signal is output at this time. However, since the distortion of the acoustic signal when the FM modulation signal of the overmodulation is received by the FM radio tuner 7 is remarkable in the high frequency part in relation to the pre-emphasis, the overmodulation signal which does not include the high frequency component. In the reception of the sound distortion of the sound is not a problem. That is, by performing the gain control only when the intensity of the high frequency component at a certain frequency or higher is high, the distortion of the reproduced sound caused by the difference in the dynamic range can be sufficiently exhibited.

It should be noted that even if the peak hold circuit 30 is not used as the gain control section in the embodiment of FIG. 3 and the conventional gain control circuit 9 as shown in FIG. it can. Also, attenuators 34a and 35a
As the high frequency component of the composite signal 26 is high without using a high frequency attenuator, the reproduction signals 21 and 2
You may make it suppress all the 2 frequency components. Also,
In the above embodiment, the modulation output device for sending the reproduction output of the CD to the FM radio tuner has been described, but the reproduction output is not necessarily limited to the CD and may be an analog or digital tape reproduction output. Further, the present invention is not limited to the case where a modulation output is given to the FM radio tuner, and any output device that gives a modulation signal to a receiving section having a different dynamic range can be implemented.

Further, the device is not limited to FM modulation, and may be a device that outputs a modulated wave of AM modulation. Further, the automatic gain control device according to the present invention is not used only in the modulation output device, but in the case of demodulating an input signal (received signal) such as a front end of a receiver, the input signal (received signal) It can be implemented even when the suppression is given according to the strength.

[0031]

As described above, according to the present invention, it is possible to obtain an automatic gain control device capable of suppressing excessive input immediately after inputting a signal, for example.

[Brief description of drawings]

FIG. 1 is a circuit block diagram of a modulation output device using an automatic gain control device according to a first embodiment of the present invention,

FIG. 2 is a circuit block diagram of a modulation output device using an automatic gain control device according to a second embodiment of the present invention,

FIG. 3 is a circuit block diagram of a modulation output device using an automatic gain control device according to a third embodiment of the present invention,

FIG. 4A is a diagram showing a strength change of a composite signal in the automatic gain control device of the first embodiment, and FIG. 4B is a diagram showing a strength change of a gain control voltage in the first embodiment,

5A is a diagram showing a change in intensity of a composite signal when there is no limiter in the second embodiment, FIG. 5B is a diagram showing a change in gain control voltage, and FIG. 5C is a diagram showing a limiter provided. Diagram showing the strength change of the composite signal in the case,

FIG. 6 is a circuit block diagram of a modulation output device using a conventional automatic gain control device,

7A is a diagram showing a change in strength of a composite signal in a conventional example, and FIG. 7B is a diagram showing a change in strength of a gain control voltage in the same example in the prior art;

[Explanation of symbols]

 7 FM Radio Tuner 20 Modulation Output Device 21, 22 Playback Signal 25 Stereo Modulation Section 26 Composite Signal 27 FM Modulation Section 30 Peak Hold Circuit 33 Gain Control Voltage 34, 35 Input Control Section (Attenuator) 42 Limiter 45 High Pass Filter

Claims (3)

[Claims] 1. An automatic gain, comprising: a gain control unit that detects the strength of an input signal and outputs a gain control power; and an input control unit that changes the strength of the input signal according to the gain control power. In the control device, the gain control unit is configured by a peak hold circuit, and the automatic gain control device is provided. 2. An automatic gain provided with a gain control section for detecting the strength of an input signal and outputting a gain control power, and an input control section for changing the strength of the input signal according to the gain control power. The automatic gain control device, wherein the control device is provided with an amplitude limiting circuit that limits the amplitude of the signal suppressed by the input control unit. 3. A gain control section for detecting the strength of an input signal and outputting a gain control power, and an input control section for changing the strength of an input signal to the modulation section according to the gain control power. In the automatic gain control device described above, the input signal is pre-emphasis processed, and the input signal is input to the gain control unit via a high pass filter.