JPH07111442A - Waveform shaping circuit - Google Patents

Abstract

PURPOSE:To suppress the production of an output signal due to noise when no input signal is received by providing a hysteresis characteristic on the waveform shaping circuit. CONSTITUTION:An input signal amplified by a differential amplifier 2 is amplified by a 1st stage amplifier circuit including a transistor(TR) 6 and further amplified by a 2nd stage amplifier circuit 15 including TRs 16, 17. An output of the differential amplifier turns on/off a TR 6 depending on a collector current of TRs 7, 8 flowing through current mirror circuits 3, 4, 5. Then a feedback circuit 18 comprising the current mirror circuit comprising TRs 19-23 and a current mirror circuit comprising a constant current source 24 and TRs 25-27 is used to apply a control signal corresponding to the output level to the input of the TR 6. Positive feedback is applied to the base of the TRs of the amplifier stage to provide an offset to the circuit thereby producing a hysteresis characteristic, and then the amplifier stage is not operated even with application of noise when no input signal is received and erroneous output is prevented.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a waveform shaping circuit having a hysteresis characteristic.

[0002]

2. Description of the Related Art FIG. 2 shows a conventional waveform shaping circuit. Figure 2
In, the input signal applied to the input terminal (1) is amplified in the differential amplifier (2), and then the transistor (6) is passed through the current mirror circuits (3), (4) and (5).
Supplied to the base of. When the level of the input signal in the differential amplifier (2) is larger than the reference voltage applied to the base side of the transistor (7), the collector current of the transistor (7) becomes larger than the collector current of the transistor (8), and 6) is off, so "H"
A level output signal is generated at the output terminal (9). When the level of the input signal is smaller than the reference voltage, the collector current of the transistor (8) becomes larger than the collector current of the transistor (7), and the transistor (6) is turned on, so that an “L” level output signal is generated. To do.

On the other hand, the input signal is also applied to the differential amplifier (10). The input signal level is transistor (1
If it is larger than the reference voltage applied to the base side of 1),
Since the collector current of the transistor (12) becomes larger than the collector current of the transistor (13), the capacitor (14) is charged. Therefore, the condenser (1
The terminal voltage of 4) rises and the reference voltage rises. On the contrary, when the level of the input signal is lower than the reference voltage, the collector current of the transistor (13) increases and the capacitor (14) is discharged, so that the reference voltage decreases.

Here, if the charge / discharge constant of the capacitor (14) is set sufficiently large, the change in the reference voltage does not follow the frequency of the input signal but can follow the change in the average level of the input signal. Therefore, the waveform shaping circuit of FIG. 2 can perform accurate waveform shaping according to the input AC signal and generate a square wave output.

[0005]

However, the waveform shaping circuit of FIG. 2 has a problem that an output signal is generated from the output terminal (9) by a minute signal such as noise when the input signal is not applied. It was That is, when there is no signal applied to the input terminal (1) and there is only the bias voltage, the reference voltage follows the bias voltage and becomes equal to the bias voltage of the input terminal (1). When a minute signal such as noise is applied to the differential amplifier (2), it is amplified by the differential amplifier (2) to turn the transistor (6) on or off, and an output signal is generated from the output terminal (9).

[0006]

SUMMARY OF THE INVENTION The present invention has been made in view of the above points, and is of an input stage amplifying circuit for amplifying an input signal and an output variable type for generating a reference voltage of the input stage amplifying circuit. A reference voltage generation circuit, a control circuit that compares an output voltage of the reference voltage generation circuit and an input signal, and changes the output voltage of the reference voltage generation circuit according to the difference, and an output signal of the input stage amplification circuit A first output stage amplifying circuit for amplifying
A second output stage amplifying circuit that amplifies the output signal of the first output stage amplifying circuit, and an output signal level of the first output stage amplifying circuit are detected, and a control signal corresponding thereto is detected by the first output stage amplifying circuit. And a feedback circuit for positively feeding back to the input.

Further, the reference voltage generating circuit is composed of a capacitor whose one end is grounded, and the terminal voltage of the capacitor is applied to the input stage amplifying circuit as a reference voltage.

[0008]

According to the present invention, the input signal is amplified in the input stage amplifier circuit and further amplified in the first output stage amplifier circuit. Further, the input signal is compared with the reference voltage generated by the reference voltage generating circuit in the control circuit, and the control circuit varies the reference voltage from the reference voltage generating circuit according to the difference. On the other hand, the output signal of the first output stage amplifier circuit is amplified by the second output stage amplifier circuit, the output signal is applied to the feedback circuit, the level thereof is detected, and the feedback circuit performs control according to the level. The signal is applied to the input of the first output stage amplifier circuit.

[0009]

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 is a diagram showing an embodiment of the present invention. The same elements as those of the conventional circuit of FIG. In FIG. 1, (15) is composed of transistors (16) and (17), and a second output stage amplifier circuit for amplifying a collector output signal of the transistor (6) constituting the first output stage amplifier circuit, (18) is A current mirror circuit comprising transistors (19) and (20) for amplifying the output signal of the transistor (6), and transistors (21), (22) and (23) for inverting the output current of the transistor (20), A constant current source (24) and transistors (25), (2) that invert the output current of the constant current source
6) and a current mirror circuit composed of (27).

Next, the operation of the circuit shown in FIG. 1 will be described. The input signal applied through the input terminal (1) is amplified in the differential amplifier (2), and the current mirror circuit (3),
A current flows through the collectors of the transistors (7) and (8) via (4) and (5). Then, the transistor (6) is turned on and off depending on the magnitude of the collector current of each of the transistors (7) and (8), and accordingly, the collector of the transistor (6) outputs “L” or “H” level output. Occurs.

The collector output of the transistor (6) is amplified by the transistor (19) and generated via the output terminal (9). Further, similarly to the above, the transistor (20) is turned on or off by the output of the transistor (6). Further, the current I ₁ flowing through the current source (24) passes through the transistor (25) to the transistors (26) and (2
It occurs in the collector of 7). The collector current I ₁ of the transistor (21) is generated in the collectors of the transistors (22) and (23) mirror-connected to the transistor (21). Then, the current obtained by adding the collector currents of the transistors (22), (23) and (26) is supplied to the base of the transistor (6).

For example, when the collector current of the transistor (8) is large and the collector current of the transistor (7) is small, the transistor (6) is turned on and its collector output becomes "L" level. Therefore, the transistor (16)
Turns off and its collector output goes to "H" level, so that the transistor (17) turns on and an "L" level output is generated from the output terminal (9). Similarly, the "L" level collector output of the transistor (6) turns off the transistor (19) and turns on the transistor (20). Therefore, the collector current I ₁ of the transistor (27)
Flows through the transistor (20), the transistors (21), (22) and (23) are turned off, and the reversal current I ₁ of the transistor (26) is changed to the transistor (2).
The current I ₁ is supplied to the base of the transistor (6), which is cut off at 2) and (23).

After that, even if the collector currents of the transistors (7) and (8) become equal to each other, since the current I ₁ is supplied to the base of the transistor (6), the transistor (6) is on. When the collector current of the transistor (8) is small and the collector current of the transistor (7) is large, the magnitude of the current flowing through the collector of the transistor (7) is the current I ₁ and the collector current of the transistor (8). When it becomes equal to the magnitude of the added current of the above, the base current of the transistor (6) becomes zero, so that the transistor (6) is turned off. Therefore, an "H" level output is generated from the output terminal (24).

On the contrary, when the collector current of the transistor (7) is small and the collector current of the transistor (8) is large, the output of the output terminal (9) becomes "H" level. Since the transistor (20) is turned off, the transistor (2
The collector current I ₁ of 7) is supplied to the base and collector of the transistor (21). Since the transistors (22) and (23) are in current mirror connection with the transistor (21), the current I ₁ flows through the collectors of the transistors (22) and (23). Therefore, the transistor (2
Since the current I ₁ flows through the collector of 6), the transistors (22) and (23) draw the collector current of the transistor (8) by the current I ₁ .

After that, since the collector current of the transistor (8) is large and the collector current of the transistor (7) is small, the magnitude of the current supplied to the base of the transistor (6) becomes the magnitude of the current I _1. When this happens, the transistor (6) turns on. Therefore, an "L" level output is generated from the output terminal (9). Thus, by providing positive feedback to the base of the transistor (6) according to the output of the transistor (6), a circuit configuration having a hysteresis characteristic can be obtained.

The hysteresis width is easily set by the current I ₁ of the current source (24) and the resistance value R ₁ of the resistor (28) for converting the input signal and the current.

[0017]

According to the present invention, the positive feedback is applied to the base of the transistor (6) to cause the waveform shaping circuit to have an offset, which causes the hysteresis characteristic. Therefore, the input terminal (1)
When there is no input signal applied to the transistor and the reference voltage becomes equal to the bias voltage of the input terminal (1), the transistor (6) cannot be turned on or off even if a small signal such as noise is applied. It is possible to prevent generation of an erroneous output from the output terminal (9).

[Brief description of drawings]

FIG. 1 is a circuit diagram showing an embodiment of the present invention.

FIG. 2 is a circuit diagram showing a conventional example.

[Explanation of symbols]

 2,10 Differential amplifier circuit 14 Capacitor 15 Second output stage amplifier circuit 18 Feedback circuit

Claims (2)

[Claims] 1. An input stage amplifier circuit for amplifying an input signal, an output variable type reference voltage generator circuit for generating a reference voltage of the input stage amplifier circuit, and an output voltage and an input signal of the reference voltage generator circuit. Compare
A control circuit that varies the output voltage of the reference voltage generation circuit according to the difference, a first output stage amplifier circuit that amplifies the output signal of the input stage amplifier circuit, and an output signal of the first output stage amplifier circuit. A second output stage amplifier circuit for amplifying; and a feedback circuit for detecting an output signal level of the first output stage amplifier circuit and positively feeding back a control signal corresponding thereto to an input of the first output stage amplifier circuit. A waveform shaping circuit characterized by the above. 2. The waveform shaping circuit, wherein the reference voltage generating circuit comprises a capacitor whose one end is grounded, and a terminal voltage of the capacitor is applied as a reference voltage to the input stage amplifying circuit.