JPS5952410A - Clipping circuit - Google Patents

Abstract

PURPOSE:To switch clipping levels easily by the 3rd transistor (TR) which clips a signal to the level at a specific point on a signal path on the basis of signals obtained from collector sides of the 1st and the 2nd TRs. CONSTITUTION:When a switch S1 is on and a switch S2 is off while VA>VR where VA is the voltage at the midpoint of the connection between resistances R11 and R12 and VR is the voltage of a reference voltage source, a TRQ1 is on and a TRQ2 is off; and a signal supplied to an input terminal IN0 is supplied to an output terminal OUT0 at it is through the resistances R11 and R12. Then, when Va<VR-I1.R13/2 where I1 and I2 are source currents and R13 is resistance, the TRQ1 is off and a TRQ4 off and the VA is clipped to about VR-I1.R13/2.

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field of the Invention] The present invention relates to a clipping circuit suitable for, for example, a noise reduction device for a tape recorder, and capable of switching the clipping level.

[The technical backbone of the invention]

Recently, various types of noise reduction playback have become widespread in audio tape recorders, and in cassette I tape recorders, it has become possible to sufficiently reduce hiss noise. Very good condition.

FIG. 1 shows an example of a commonly used noise reduction device, in which an encoder capable of performing noise reduction reproduction and a decoder capable of performing noise reduction reproduction are both used. In other words, it is supplied to the remote terminal IN. The signal is increased +1iiA
The signal is supplied to one input terminal of the adder 12 via the adder 11.

When the noise reduction device shown in FIG. 1 is operated as an encoder, the output signal of the amplifier 11 is supplied to the input end of the variable filter 13 via the a terminal side of the switch S. This variable filter 1
3 extracts the high frequency component of the output signal of the amplifier 1 while changing the cutoff frequency according to its level, as is well known. The output signal of the variable filter 13 is amplified by the amplifier 14 and then rectified by the rectifier circuit 16 via the amplifier J5.

The output signal of this rectifier circuit 16 is smoothed by a smoothing circuit 17 and then supplied to the control input terminal of the variable filter 1"3, which changes the impedance of a variable impedance circuit inside the variable filter 13, for example, and changes the cutoff frequency. It is something.

Further, the output signal of the buffer amplifier 14 is transmitted to the limiter circuit 18.
An encoded signal is supplied to the output terminal OUT by being supplied to the other input terminal of the adder 12 via the input terminal OUT, and the apparatus shown in FIG. 1 operates as an encoder.

On the other hand, when the device of FIG. 1 is operated as a decoder, the output signal of the adder 2 provided through the switch 5LI)b terminal
3 and the amplifier 14 to the other input terminal of the adder 3A-12. In this case, amplifier 1
The high-frequency component signal outputted from the limiter circuit 18 has an inverse phase with respect to the output No. 1 of the output signal No. 1. Therefore, in the device shown in FIG. 1, the decode signal is transmitted to the output terminal OUT.
” and is intended to operate as a decoder.

The limiter circuit 18 is provided to prevent the open neat from coming out in response to the instantaneous light input power level.

On the other hand, compared to the noise reduction method applied to the device shown in FIG. 1, an even better noise reduction effect can be obtained by connecting the devices shown in FIG. 1 in two stages in series. Noise reduction devices of this type have recently become widespread. Such a noise reduction device can be easily used to achieve the same effect as the noise reduction method of the device shown in Fig. 1 by switching the external constant and the clipping level of the limiter circuit in either the front stage or the rear stage. This method is characterized by selectively switching between the noise reduction method and the noise reduction method.

The operation level of the upper limiter circuit is switched as shown in FIG. 2, for example.

However, parts of Figure 2 that are the same as those in Figure 1 are marked with the same number.
Therefore, the explanation thereof will be omitted.

That is, the output terminal of the #i width amplifier 14 is a limiter circuit zo'? whose operation level can be changed. f:jfh is connected to the other input terminal of the adder 12 via a resistor R1°R2e R3 in series. A diode Dl with the polarity shown is connected between the connection midpoint of the resistors R2 and R3 and the ground.

A diode limiter turned on by D2 is inserted. One end of a goo limiter made of a diode DSsD4 with the polarity shown is connected to the midpoint of the connection between the resistors R1+R2, and this diode limiter is selectively driven depending on whether the transistor Qo is turned on or off. It has become so.

Note that the resistor R4#''5 is a resistor for generating a pace bias for the transistor Qo, and the switch So is a switch for controlling on/off switching of the transistor Qo.

In the limiter circuit 2o, if the resistance value of each resistor R to R3 is indicated by its sign, its clipping level vc is the transistor Q.

In the off state, R+ +R2+R3 0.7 in vc [: V) 3 When the transistor Qo is on, the clipping level is switched and the above two types of noise reduction methods are used □J Efficient noise reduction equipment 〃1? L. It is possible to configure.

[Problems with background technology]

However, the limiter circuit 20 shown in FIG. 2 does not operate unless the input signal level is sufficiently large, and the problem is that the current flowing through the transistor QO is not small.

This poses a problem in terms of heat generation, for example, when the noise reduction device is integrated into an IC (integrated circuit).

[Purpose of the invention]

The present invention has been made in view of the above points, and it is an object of the present invention to provide a good quality ripping circuit that can operate at a low signal level and can very easily switch the clipping level.

[Overview of the Invention J This invention relates to a differential pair of transistors in which the pace of an 8g1 transistor is connected to a predetermined location of a signal path, and the pace of a second transistor is connected to a reference voltage source; a resistor connected between each emitter of
a plurality of constant current sources connected to each emitter side of the differential pair transistors and forming an emitter current path of the differential pair transistors, and a switching means for selectively turning off and off at least one of the constant current sources; A third circuit clips the level of the input point of the A Δ path based on the signal obtained from the erector side of either the first transistor or the second transistor forming the differential pair transistor.
It is equipped with a transistor and can switch the clipping level! It will be on standby.

[Embodiment J of the Invention An embodiment of the invention will be described in detail below with reference to the drawings.

That is, as shown in FIG. 3, the input terminal IN. Resistors R11 and RI2, which are connected in series, are interposed and connected between the output terminals 0UTo and 0UTo. The middle point of each connection of the above-mentioned resistors Bat and RI2 is connected to the pace of the NPN type transistor Ql. This transistor Qli=1: The collector is supplied with the power supply + VCC voltage through the diode DIO with the polarity of ■1.
'1. It is connected to the terminal 21, and its emitter is grounded via the constant current source 11 and switch Sl.

On the other hand, the anode of the reference voltage 1) station v7 whose cathode is grounded is connected to the pace of the NPN transistor Q2. The collector of this transistor Q2 is connected to the collector of a PNP type transistor Q3 which will be described later, and the emitter is grounded via a constant-1 current source I2 and a switch 82 in series. In addition, the above transistor Q
A resistor RI3 is connected between the emitters of Q1 and Q2.
Interventions have been made.

The transistor Q3 is combined with the -F diode DIO to form a current mirror circuit, and the deflection pace is between the collector of the transistor Qx and the diode DI.
It is connected to the connection midpoint of the cathode of D, and the emitter is connected to the power supply terminal 2. A midpoint between the collectors of the transistors Q2 and Q3 is connected to a PNP type transistor Q40. The emitter of this transistor Q4 is connected to the power supply terminal 2, and the collector is connected to the midpoint between the resistors R11 and RI2.

That is, in the circuit configured as described above, when switch S is on and switch S2 is off, the voltage at the midpoint of the connection between resistors R11 and R12 is set to vA, and the reference voltage source V
If the voltage of FL is indicated by each sign, vA
> VR, transistor QI is turned on, transistor Q4 is turned off, and the signal provided to input terminal INo is directly transmitted to output terminal o via resistors R11 and RI2.
U.T.

It is supplied to Next, if the constant currents til+, Is and the resistance values of the resistor RI3 are indicated by their respective signs, then when Va(VRll・J3/2), the transistor Qr is turned off, the transistor Q4 is turned on, and v
A is approximately VR-I, which is clipped by RI3/2.

On the other hand, in the circuit shown in FIG. 3, when the switch Sl is off and the switch S2 is on, the voltage vA at the midpoint of the connection between the resistors R11 and L12 is approximately vR-■2・R13 when the power decreases. /2 is clipped.

In this way, the circuit of FIG. 3 uses a scale that can easily switch the clipping level, a current source of 11% current, a large resistance value of the resistor R1g, and a reference voltage source vR.
By setting the voltage low, it is possible to perform clipping operation even at a sufficiently small signal level.

FIG. 4 shows a specific example of FIG. 3, in which the current source 11
, I, switch Sl, 82, for example, transistor Qs 3 Q6, diode DII e D
Ill e D1! , differential pair transistor QteQ8,
The current source I3 and the switch S3 are constructed as shown in the figure.

FIG. 5 shows another embodiment, in which when the voltage vA at the connection midpoint of the resistors R11 and R12 increases due to the PNP transistor Q, the NPN transistor Qlo, and the constant current source I4, the voltage vA at the connection midpoint of the resistors R11 and R12 increases. Ka, t
7, VB -I 1-Rts/ 2 to VB +h
- It is configured to perform clipping at Rts/2. However, in FIG. 5, the same parts as in FIG. 3 are designated by the same reference numerals, and their explanation will be omitted.

The circuit shown in Fig. 5 can be used in place of the circuit shown in Fig. 2 by combining it with the circuit shown in Fig. 3, and can switch a suitable clipping level for the plurality of noise reduction devices described above. It is possible to construct a good limiter circuit with high performance.

FIG. 6 and FIG. 7 d1 each show still other embodiments. However, in FIGS. 6 and 7, the same parts as in FIG. 3 are designated by the same reference numerals, and the explanation thereof will be omitted.

That is, by removing the circuit a in FIG. 6 and the switch S in the circuit in FIG. The resistor RI3 is connected to the midpoint between the resistor RI3 and the resistor RI3.

The circuit shown in FIG. 7 is the same as the circuit shown in FIG. 3, except that a resistor R14 is inserted and connected between the connection midpoint of the constant current source 11 and the resistor its and the emitter of the transistor Ql.

These circuits all use differential pair transistors Ql, Q
The two circuits have different contact states with respect to the emitter side, and like the circuit shown in Figure 3, they can operate at low signal levels, and their clipping levels can be changed easily. be.

It should be noted that this invention is not limited to the above-mentioned embodiments, and it goes without saying that variations and applications of the gods may be made without departing from the gist of the invention.

〔Effect of the invention〕

As described in detail above, according to the present invention, it is possible to provide a good ripping circuit that can operate at low signal levels and can very easily switch the clipping level.

[Brief explanation of drawings]

Fig. 1 is a block diagram used to explain a conventional noise reduction device, Fig. 2 is a circuit diagram showing the limiter circuit of Fig. 1, and Fig. 3 shows an embodiment of the clipping circuit according to the present invention. FIG. 4 is a more specific circuit diagram of the circuit shown in FIG. 3, and FIGS. 5-1 to 7 are circuit diagrams showing other embodiments. Ql to QIO...transistor, DIG to DH/
...Diode, ■! to I4 constant current sources, R11 to RI4...resistors, vR...reference voltage sources, S,,S,. S3: switch, 2: power supply terminal. Issuing agent Patent attorney Takehiko Suzue Figure 1 11 Figure 2 Figure 3 Figure 1 Figure 5 65- Figure 6 Figure 7

Claims (1)

[Claims] The base of the first transistor is connected to a predetermined point of the signal path, and the base of the second transistor is connected between a differential pair transistor connected to a reference voltage source and each emitter of the differential pair transistor. a resistor, a plurality of constant current sources connected to each emitter side of the differential pair transistors and forming an emitter current path of the differential pair transistors, and selectively turning on and off at least one of these constant current sources. a switching means, a third transistor and metal fittings for clipping the level of a predetermined location of the route 48 based on a signal obtained from the collector side of either the first transistor or the second transistor forming the differential pair transistors; A clipping circuit is characterized in that the clipping level can be changed.