JP2547732B2 - Limiter circuit - Google Patents

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a limiter circuit for limiting a signal amplitude, and more particularly to prevention of a decrease in dynamic range.

[Conventional technology]

Conventionally, VTR (video tape recorder) audio recording and
When trying to achieve high fidelity (Hi-Fi) in playback, the FM recording / playback method is adopted.

By the way, in the Hi-Fi recording / reproducing VTR, since the stereo 2-channel audio FM signal is inserted in the narrow frequency band between the luminance signal (low carrier FM signal) and the low frequency conversion color signal, the luminance signal The maximum frequency deviation (± 150kHz in the VHS standard) for the audio FM signal is determined to prevent interference between the low frequency conversion color signal and the audio FM signal, and a limiter circuit is used at the audio signal stage so as not to exceed this range. Amplitude is restricted by.

FIG. 9 shows a VTR audio signal system of a general FM recording / reproducing system. In the FM recording / reproducing method, at the time of recording, the audio signal applied to the input terminal 2 is passed through the logarithmic compression / expansion type noise reduction circuit (PNR) 4 and is added to the limiter circuit 6, and the amplitude is increased by the limiter circuit 6. After limiting to a certain value or less, a specific carrier wave is FM-modulated in addition to the FM modulation circuit (FMMOD) 8 and the modulated output is added to the magnetic head 10 and recorded on a magnetic tape. In this case, the limiter circuit 6
Is composed of a resistor 12 and diodes 14 and 16.

During reproduction, the FM signal obtained through the magnetic head 10 is added to the FM demodulation circuit (FMDEM) 18, the audio signal is demodulated from the FM signal, and the demodulated output is output via the noise reduction circuit 20. Output from the terminal 22 to the audio playback system.

[Problems to be solved by the invention]

By the way, in the FM recording / reproducing system using such a limiter circuit 6, when the audio input signal is encoded by the logarithmic compression / expansion type noise reduction circuit 4, the audio input signal (the audio Signal), the dynamic range is significantly compressed (for example, 100d by the logarithmic compression effect of the noise reduction circuit 4).
Since the signal component having the dynamic range of B is compressed to 50 dB), the limiter circuit 6 never reaches a level where the amplitude is limited. For example, as shown in A of FIG. 10, when an audio input signal whose level fluctuation is gentle is applied to the noise reduction circuit 4, the encoded output (recording output signal) of the noise reduction circuit 4 is as shown in FIG. As shown in B, since it is logarithmically compressed within the range of the limit voltage levels V _C1 and V _C2 set in the limiter circuit 6, such an audio input signal is passed through the limiter circuit 6 and then passed through the FM modulation circuit 8. When magnetically recorded, the reproduction output signal can faithfully restore the original signal as shown in C of FIG.

However, the input signal contains a lot of high frequencies, and for a passive signal (dynamic signal) whose level changes drastically,
The dynamic range is difficult to be compressed due to the attack time constant of the noise reduction circuit 4 and the effect of pre-emphasis, and sometimes the limiter circuit 6 often limits the amplitude even at a normal input level. That is, when the signal level suddenly increases, the logarithmic compression cannot follow instantaneously due to the delay of the time constant circuit, and the level is further enhanced by the high-frequency enhancement effect of pre-emphasis, and the compression effect of the dynamic range is increased. Is less. When these signals are recorded and reproduced with the amplitude limited by the limiter circuit 6, the reproduced output signal has a slow rising waveform and cannot restore the original signal. From the auditory sense, the high-frequency sounds that are pulsative are cut off, and the impression is that the frequency characteristics in the high-frequency range have deteriorated. For example, as shown in FIG. 11A, when an audio input signal with a large level variation is applied to the noise reduction circuit 4, the encoded output (recording output signal) of the noise reduction circuit 4 is
As shown in FIG. 11B, since the limiter circuit 6 has a steep signal component exceeding the range of the limiting levels V _C1 and V _C2 set, if such a voice input signal is passed through the limiter circuit 6, , The signal portion exceeding the limiting levels V _C1 and V _C2 is scraped off by the limiter circuit 6,
When the audio input signal from which such a signal component is deleted is magnetically recorded through the FM modulation circuit 8, the reproduction output signal is
As shown in C of FIG. 11, the original signal cannot be faithfully restored and the dynamic range is reduced.

In such an FM recording / playback system, the limiter circuit 6 is indispensable for preventing interference between FM frequencies, but due to the nature of the noise reduction circuit 4, the limiter circuit 6 for preventing overmodulation causes the static noise to be suppressed. The dynamic range of recording and playback changes significantly between the dynamic input signal and the dynamic input signal, and the dynamic range narrows with the dynamic signal. Therefore, the limiter is especially effective for a sound source with many dynamic signal components. The operating characteristic of the circuit 6 becomes a problem.

SUMMARY OF THE INVENTION Therefore, an object of the present invention is to provide a limiter circuit in which the dynamic range is not deteriorated even when the level change is abrupt.

[Means for solving problems]

The limiter circuit of the present invention is, as illustrated in FIG. 1, a limiter circuit installed in an FM recording / reproducing system, which selectively switches between an audio input signal to be recorded and a reproduced FM signal. 1 switching means (switch 26) and an amplifier (operational amplifier) for amplifying the voice input signal or the FM signal applied from the first switching means to the positive phase input side.
32), a first signal path (34a) that forms a feedback circuit between the output section of the amplifier and the negative-phase input side to totally feed back the output signal of the amplifier to the negative-phase input side, and A second signal path is formed between the output section of the amplifier and the negative phase input side to form a feedback circuit, and the output signal of the amplifier is fed back to the negative phase input side through the resistor (36) ( 34b)
And between the first signal path and the second signal path and the negative phase input side of the amplifier, the first signal path to the negative phase input side of the amplifier or Second switching means (switch 40) for selecting and connecting the second signal path, and an output signal of the amplifier, which is added to the output side of the amplifier through the resistor, or feedback of the second signal path. A signal is provided with a voltage limiter (38) whose impedance changes when the level of the signal exceeds a predetermined level. When recording the audio input signal, the audio input signal is amplified by the amplifier and the output signal thereof is provided. Is fed back to the negative phase input side through a first signal path, and the voltage limiter is connected to the output side of the amplifier through the resistor so that the output signal from the second signal path side is on the FM modulation means side. When the FM signal is reproduced, the reproduced FM signal is added to the amplifier and amplified, and the output signal is fed back from the second signal path side to the anti-phase input side through the resistor. The output signal is extracted after being amplified by the amplifier.

In other words, the limiter circuit of the present invention, for example,
When the recording / playback method is implemented, the amplitude is expanded during playback to limit the amplitude during recording, and the signal amplitude is expanded / contracted as necessary to substantially improve the dynamic range regardless of the recording / playback mode. It is in.

[Action]

The limiter circuit of the present invention selects a signal path of a feedback circuit for an amplifier according to an input signal selected from a plurality of input signals, and adds a voltage limiter to the feedback circuit by selecting the signal path. . For example, for a certain input signal, a total feedback amplifier is constituted by an amplifier and a feedback circuit to form a buffer amplifier, the amplitude of the signal passing through the buffer amplifier is limited by a voltage limiter, and for another input signal, a voltage limiter is used. The original signal is reproduced by extending the amplitude through the added feedback circuit.

Therefore, even if the signal that requires amplitude limitation contains a sharp attack component, the attack component is not impaired, and a decrease in the dynamic range of the signal is prevented,
For example, even when the signal is FM-modulated and magnetically recorded, the amplitude of the signal reproduced from the magnetic recording can be compensated by the characteristic opposite to that at the time of recording at the time of recording, and the original signal can be faithfully reproduced.

〔Example〕

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

 FIG. 1 shows an embodiment of the limiter circuit of the present invention.

In the embodiment shown in FIG. 1, the limiter circuit 24 according to the present invention is installed in the FM recording / reproducing system shown in FIG. In the limiter circuit 24, the switch 26 provided as the first switching means selects an input signal to be applied to the non-inverting input terminal (+) of the operational amplifier 32 from a plurality of input signals applied to the input terminals 28 and 30. The audio input signal to be recorded from the noise reduction circuit 4 is added to the contact R side, and the FM demodulation circuit 18 demodulates the FM signal detected by the magnetic head 10 to the contact P side. The audio signal has been added.

Between the output side of the operational amplifier 32 and the inverting input terminal (-), a feedback circuit 34 for feeding back the output of the operational amplifier 32 to the input side.
Is added. The feedback circuit 34 has a first signal path 34a that directly connects the output side to the inverting input terminal (-),
A second signal path 34 including a resistor 36 between the output side and the inverting input terminal (-) and a voltage limiter 38 is added.
b and each signal path 34a, 34b is selectively switchable by a switch 40 provided as a second switching means.

The output side of the operational amplifier 32 has two output terminals.
42 and 44 are provided, and an audio signal as a reproduction output from the output terminal 42 and an audio signal to be recorded are selectively taken out from the output terminal 44. Therefore, the audio signal extracted from the output terminal 42 is added to the noise reduction circuit 20,
Further, the audio signal taken out from the output terminal 44 is added to the FM modulation circuit 8. The audio signal applied to the FM modulation circuit 8 is FM-modulated on the carrier wave for magnetic recording, and the modulated output is applied to the magnetic head 10 and magnetically recorded on the magnetic tape.

Therefore, in the recording mode, in the limiter circuit 24, the switches 26 and 40 are switched to the contact R side, and after the switch 26 is switched to the contact R side, the audio signal from the input terminal 2 side passes through the noise reduction circuit 4. , The non-inverting input terminal (+) of the operational amplifier 32. in this case,
By switching the switch 40 to the contact R side, the feedback circuit 34
Is a form in which the output side of the operational amplifier 32 and the inverting input terminal (-) are directly connected.
As shown in FIG. 2, an all-feedback amplifier 32 'is constructed, a resistor 36 is inserted in series between the all-feedback amplifier 32' and the FM modulation circuit 8, and a voltage limiter 38 is inserted with the resistor 36. The signal path 34b is added to the FM modulation circuit 8 side. In this case, the all-feedback amplifier 32 ′ simply functions as a buffer amplifier for the audio signal to be recorded, and the voltage limiter 38 operates via the resistor 36 so that the amplitude-limited audio signal is output.
It is added to the FM modulation circuit 8. Therefore, the audio signal whose amplitude has been limited is recorded on the magnetic tape from the magnetic head 10 through FM modulation. In this case, since it is the recording mode, the noise reduction circuit 20 and FM of the playback system
The demodulation circuit 18 has stopped operating.

Further, in the reproduction mode, the switches 26 and 40 are switched to the contact P side, and by switching the switch 26 to the contact P side, the FM signal is added from the magnetic head 10 side to the FM demodulation circuit 18, and the demodulated output is obtained. The audio signal is applied to the non-inverting input terminal (+) of the operational amplifier 32. In this case, switch 40
By switching the contact point to the contact P side, as shown in FIG.
The feedback circuit 34 has a configuration in which the resistor 36 is inserted between the output side of the operational amplifier 32 and the inverting input terminal (-), and the signal path 34 on the inverting input terminal (-) side of the operational amplifier 32 is provided.
A voltage limiter 38 is added to b.

In this case, the feedback circuit 34 includes a resistor 36 and a voltage limiter 38.
Is added, the characteristics have an inverse characteristic with respect to the amplitude limit by the voltage limiter 38 at the time of recording, and the original signal at the time of recording is reproduced by compensating for the amplitude limit of the voltage limiter 38 at the time of recording. Therefore, the voice signal whose original signal amplitude is restored is
It is taken out from the output terminal 22 via the noise reduction circuit 20.

In the limiter circuit 24, the voltage limiter 38 has
It has no temperature characteristics and stable operation can be obtained.
It is ideal to use a device that can obtain a gentle amplitude limiting operation when the voltage exceeds a specific limiting voltage, in that no signal distortion is caused and that the original signal is restored. Further, as a matter of course, when such a limiter circuit 24 is used in the recording / reproducing system, at the time of recording, the signal at the input portion of the FM modulation circuit 8 is FM modulated, recorded on a magnetic tape, detected and FM demodulated. It is necessary to occur with exactly the same amplitude as the signal after being processed. Then, in the recording / reproducing system, in order to make the signal amplitude at the time of recording equal to that at the time of reproducing, for example, at the time of recording, FM modulation is performed by using the voltage controlled oscillator in the FM modulation circuit 8, and at the time of reproduction, the FM modulation circuit. 8
PLL (Phase Locked Loop) type F using the voltage controlled oscillator of
By configuring the M demodulation circuit 18, if the frequency control sensitivity of the voltage controlled oscillator is set to be exactly the same during recording and reproduction, the signal reproduced from the magnetic recording is FM-demodulated through FM modulation and magnetic recording. The signal obtained in this case and the original signal can have the same amplitude.

FIG. 4 shows a concrete circuit configuration example of the limiter circuit 24 shown in FIG.

As shown in FIG. 4, an audio signal to be reproduced at the time of reproduction is added to the input terminal 28, and an audio signal to be recorded at the time of recording is added to the input terminal 30. In this case, the input terminals 28 and 30 do not assume external terminals (pins) of the IC.

The operational amplifier 32 is configured with two differential amplifiers 46A and 46B as pre-stage amplifiers and one output stage amplifier 48 to which switches 26 and 40 are added, and the differential amplifier 49A is for reproduction and differential. The amplifier 46B is set for recording, and its operation can be switched depending on the recording / reproducing mode. That is, the differential amplifier 46A includes the transistors 50, 5
2, 54, 56, 58 and resistors 60, 62, 64, 66. During reproduction, a bias input V _P as a control voltage is applied to the base of the transistor 54 to activate the transistor. Also,
The differential amplifier 46B is the transistors 56 and 58 of the differential amplifier 46A.
And resistors 60, 62 in common, transistors 68, 7
It is composed of 0 and 72 and a resistor 74, and at the time of recording, a bias input V _R as a control voltage is applied to the base of the transistor 72 to be in an operating state. The constant bias voltage V applied to the bias input terminal 76 is applied to the bases of the transistors 50 and 68 that form the input section of the differential amplifiers 46A and 46B.
_B is the base side of the transistor 50 through the resistors 78 and 66,
Applied to the base side of the transistor 68 via a resistor 80,
The bias voltage V _B is set to a voltage value that is half the power supply voltage V _CC , for example.

The output stage amplifier 48 includes transistors 82, 84, 86,
Composed of 88 and resistors 90, 92, 94, 96, transistor
82 is a transistor 56 installed as a load for the differential amplifiers 46A, 49B, and transistor 84 is a differential amplifier 46A, 4B.
It forms a current mirror circuit with the transistor 58 installed as a 6B load. In this case, during playback, the playback signal
PB is taken out from the output terminal 42 provided on the collector side of the transistors 84 and 88. Resistor 36 is an output stage amplifier 48
Is installed between the common collector of the transistors 84 and 88, which is the output terminal of the transistor, and the base of the transistor 52 on the inverting input terminal (-) side of the differential amplifier 46A. Then, at the time of recording, the output signal REC to be recorded is taken out from the output terminal 44 formed on the base side of the transistor 52.

Further, the voltage limiter 38 has a function of suppressing the signal amplitude by decreasing the impedance when the audio signal amplitude exceeds a specific level, and is symmetrical to the positive and negative sides with respect to the specific midpoint level voltage V _B. Set the allowable amplitude V _C1 to the positive side limiter 10 so that the positive and negative side amplitudes are uniformly limited.
It is composed of 0A and a negative limiter 100B whose allowable amplitude is set by V _C2 . In this case, the positive side limiter 100A includes the transistors 102, 104, 106 and 108 and the resistors 110, 112 and 11.
4, 116, and the negative side limiter 100B includes transistors 118, 120, 122, 124 and resistors 126, 128, 130, 1
It consists of 32. And resistors 134, 136, 138, 1
The series resistor circuit consisting of 40 constitutes a voltage divider circuit,
Limiting voltages V _C1 and V _C2 are symmetrically set on the positive and negative sides with respect to a specific midpoint level set by V _B. In this case, the bias voltage V _B set at the midpoint of the resistors 136 and 138 is shared with the bias voltage of the operational amplifier 32, and the midpoint level of the audio signal during recording and the midpoint of the audio signal during playback are set. Make sure the levels match.

Further, the transistors 142, 144, 146, 148, 150 and the resistors 152, 154, 156, 158, 160 constitute a constant current circuit which gives an operating current to the positive and negative limiters 100A, 100B. Depending on the control voltage V _L set at the base of the transistor 150, the positive and negative limiters 100A, 10
0B works.

Regarding the limiting operation, focusing on the positive side limiter 100A shown in FIG. 5, the resistance values of the resistors 110 and 112 are R _E , the resistance value of the resistor 36 is R _NF , and the transistor 142 forming the constant current source. The constant current supplied from I ₀ is supplied to the transistor 104 by supplying a signal voltage exceeding the limiting amplitude level.
The current flowing through the current flowing through the I _1, the transistor 102 I ₂
Then, the voltage level ΔV exceeding the limit amplitude level is ΔV = R _E (I ₁ −I ₂ ) + V _T 1n (I ₁ / I ₂ ) ... (1). However, V _T is given by V _T = kT / q and is a constant voltage obtained from Boltzmann's constant k, temperature T (° K) and charge q. And V _T 1n (I ₁ / I ₂ ) ≪ R _E (I ₁ −I ₂ ).
At this time, the voltage level ΔV is ΔV≈R _E (I ₁ −I ₂ ) ... (2). Further, the constant current I ₀ and the currents I ₁ and I ₂ have a relationship of I ₀ = I ₁ + I ₂ (3). Here, assuming that the resistance values of the resistors 114 and 116 are R ₁ and R ₁ · I ₁ >> V _T 1n (I ₁ / ΔI), the voltage level Δ
Current [Delta] I flowing through the transistor 106 corresponds to the V becomes _{ΔI ≒ I 1 -I 2 ≒ ΔV} / R E ...... (4).

Therefore, the input impedance R _IN of the positive side limiter 100A
Is R _IN = ΔV / ΔI≈R _E (5)

Therefore, for an input exceeding the voltage V _C1 , a voltage _divided by the input impedance (R _IN ≈R _E ) and the resistor 36 (R _NF ) can be obtained. Therefore, limiting is not performed completely, the amplitude is limited in a form in which the level is attenuated, the limiting level is determined by voltage division with the power supply, and the attenuation amount is also almost determined by the resistors 36, 110, 112, etc. The influence of temperature etc. is very small. Such an operation is the same for the negative limiter 100B.

Therefore, with the operation of the voltage limiter 38, the control voltages V _P and V _R for the transistors 54 and 72 cause the recording,
Switching the playback mode, a differential amplifier according to each mode
46A and 46B are selectively operated, and the signal paths 34a and 34b of the feedback circuit 34 are switched.

At the time of recording, since the buffer amplifier is constituted by the differential amplifier 46B, the output stage amplifier 48 and the feedback circuit 34, the input signal to be recorded applied to the input terminal 28 passes through the differential amplifier 46B and is output stage amplifier. Taken as buffer output from 48. This buffer output signal is applied to the voltage limiter 38 via the resistor 36. Since the voltage limiter 38 has the input / output characteristics as shown in FIG. 6, the recording input as shown at A in FIG. Signal amplitude is positive limit voltage
When _exceeding V _C1 and negative limit voltage V _C2 , positive limit voltage
A gentle amplitude limiting operation is performed according to the amplitude _exceeding V _C1 and the negative side limiting voltage V _C2 , and as shown in FIG. 7B, it is converted into a recording output signal having a certain amplitude or less and output terminal 44 Taken from.

During reproduction, the input signal to be reproduced which is applied to the input terminal 30 is output as the output signal PB from the output stage amplifier 48 via the differential amplifier 46A. In this case, the resistor 36 is inserted in the feedback circuit 34, and the voltage limiter 38 is added to obtain the input / output characteristic for expanding the amplitude limit during recording as shown in FIG. The amplitude of the reproduced signal is compensated by the input / output characteristics, and the original signal at the time of recording is faithfully reproduced. For example, as shown in FIG. 7C, when a reproduction input signal whose amplitude is limited is applied, amplitude compensation is applied to the part where the signal component is scraped off due to the input / output characteristics shown in FIG. , As shown in FIG. 7D, A in FIG.
The same output signal as the input signal at the time of recording shown in is reproduced, and the original signal is faithfully reproduced. That is, at the time of recording, for the input signal whose level is small enough not to apply the amplitude limitation, the resistor 36 is simply added between the output side of the operational amplifier 32 and the inverting input terminal (-) to provide the total feedback. Since the input and output signals are in the same amplitude state, when the level is large and the voltage reaches the voltage at which the voltage limiter 38 works, the amplitude is limited to the positive and negative parts in the signal paths 34a and 34b of the feedback circuit 34. Is added, the amplitude of the input signal is expanded, and the amplitude limitation at the time of recording is released and compensated to restore the original signal. In this case, also with respect to the amplitude expanding operation of the voltage limiter 38, similarly to the amplitude limiting operation, a gentle amplitude expanding operation according to the amplitude level can be obtained.

Therefore, according to the configuration of this embodiment, the amplitude limit start voltage is stable, the amplitude limit is moderately performed, and the limiter circuit that is stable with respect to temperature is used to add the amplitude limit during recording. Also, even if the same limiter circuit is used as the feedback system of the operational amplifier during reproduction and the signal exceeding the limiting voltage is amplitude-limited to below the limiting voltage level, the limited part can be faithfully restored to the original signal. Also, the same effect as expanding the dynamic range of the FM recording / playback system, that is, the maximum frequency deviation can be obtained. Therefore, it is possible to extend the dynamic range of the recording / playback system including noise reduction, not only to the pulsive signal but also to the static signal, and to easily and faithfully reproduce the original signal in the recording / playback system. Can be reproduced.

In addition, in the case other than self-recording / reproducing in which the recording / reproducing system can be shared, for example, when reproducing a recording such as a magnetic tape recorded by another recording device, the limiter control voltage V _L is set to H (ON). / L (OFF) {however, H is high potential and L is ground (GND) potential} stops the limiting operation and cancels the limiting expansion at the time of reproduction, thereby reproducing in the normal mode. That is, in this control, the recording and reproduction control voltages V _P and V _{R are} controlled by the control circuit, and during recording, V _P is L, V _R is H, V _L is H, and during extended reproduction, V _P is H, V _R is set to L, V _L is set to H, and during normal reproduction, V _P is set to H, V _R is set to L, and V _L is set to L.

Although the amplitude limitation of the audio signal in the recording / reproducing system is described in the embodiment, the present invention can be applied to the case where the amplitudes of a plurality of signals other than the recording / reproducing system are adjusted according to the signal. Further, although a magnetic tape is taken as an example of the recording means, the present invention can be similarly applied to a recording medium other than the magnetic tape.

As described above, according to the present invention, the signal path of the feedback circuit for the amplifier is selected according to the input signal selected from the plurality of input signals, and the signal path is selected by selecting the signal path. A voltage limiter is added to the feedback circuit.For example, for a certain input signal, an amplifier and the feedback circuit form a total feedback amplifier to form a buffer amplifier, and the amplitude of the signal passing through the buffer amplifier is limited by the voltage limiter. Also, for other input signals, the amplitude is expanded and the original signal is reproduced through a feedback circuit with a voltage limiter added, so not only the signal whose level changes gently,
Amplitude limiting and amplitude expanding can be performed on a signal whose level changes abruptly, and the reduction of the dynamic range of the signal due to amplitude limiting can be prevented, so that the original signal can be easily and faithfully reproduced.

[Brief description of drawings]

FIG. 1 is a circuit diagram showing an embodiment of the limiter circuit of the present invention, FIG. 2 is a circuit diagram showing an equivalent circuit in the recording mode of the limiter circuit shown in FIG. 1, and FIG. 3 is shown in FIG. FIG. 4 is a circuit diagram showing an equivalent circuit of the limiter circuit in a reproduction mode, FIG. 4 is a circuit diagram showing a concrete circuit configuration example of the limiter circuit shown in FIG. 1, and FIG. 5 is a diagram showing the voltage limiter shown in FIG. FIG. 6 is a circuit diagram showing a positive side limiter, FIG. 6 is a diagram showing input / output characteristics of the limiter circuit shown in FIG. 4 in a recording mode, and FIG. 7 is an operation of the limiter circuit shown in FIG. 4 in a recording and reproducing mode. FIG. 8 is a diagram showing waveforms, FIG. 8 is a diagram showing input / output characteristics in the reproducing mode of the limiter circuit shown in FIG. 4, and FIG. 9 is a block diagram showing a conventional FM recording / reproducing system, FIGS. 10 and 11. The figure shows the operating waveforms of the FM recording / playback system shown in Fig. 9. It illustrates. 24 …… Limiter circuit 26 …… Switch (first switching means) 32 …… Operational amplifier (amplifier) 34 …… Feedback circuit 34a …… First signal path 34b …… Second signal path 38 …… Voltage limiter 40 ... Switch (second switching means)

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor, Yoshiyoshi Izawa, 21, Saizo Mizozaki-cho, Ukyo-ku, Kyoto ROHM Co., Ltd. (56) Reference JP-A-56-137722 (JP, A)

Claims (1)

(57) [Claims] 1. A limiter circuit installed in an FM recording / reproducing system, comprising first switching means for selectively switching between an audio input signal to be recorded and a reproduced FM signal, and the first switching means. An amplifier for amplifying the voice input signal or the FM signal applied from the means to the positive phase input side, and a feedback circuit between the output section of the amplifier and the negative phase input side to form the output signal of the amplifier. A first signal path for performing full feedback to the negative-phase input side and a feedback circuit formed between the output section of the amplifier and the negative-phase input side to form an output signal of the amplifier by the negative-phase input. A second signal path for returning to a side through a resistor, and the first signal path and the second signal path and the inverting input side of the amplifier, and the inverting signal of the amplifier. The first signal path or the second signal path to the phase input side. Second switching means for selecting and connecting a path, and a level that is added to the output side of the amplifier through the resistor and has a predetermined level with respect to the output signal of the amplifier or the feedback signal of the second signal path. A voltage limiter whose impedance changes when it exceeds the above-mentioned, and when the voice input signal is recorded, the voice input signal is amplified by the amplifier, and the output signal thereof is input through the first signal path to the reverse phase input. The output side of the amplifier, the voltage limiter is connected to the output side of the amplifier via the resistor, the output signal is output from the second signal path side to the FM modulation means side, and when the FM signal is reproduced, The reproduced FM signal is added to the amplifier and amplified, and the output signal is fed back from the second signal path side to the anti-phase input side through the resistor and amplified by the amplifier. A limiter circuit characterized by taking out an output signal.