JPS59147528A - Schmitt circuit - Google Patents

Abstract

PURPOSE:To obtain suitably a comparatively small Schmitt trigger level by deciding the Schmitt level from a forward voltage difference of a diode produced by a current ratio set between semiconductor devices. CONSTITUTION:Transistors (TRs) 3, 4 form a differential amplifier, to which loads TRs 1, 2 are connected. Further, the base potential of the TRs 3, 4 is decided by a cathode potential of diodes 12, 13. Since the anodes of the diodes 12, 13 are connected in common and connected to a bias power supply 25 having a prescribed potential V2, the cathode potential of the diodes 12, 13 depends on the current flowing to each diode. The Schmitt level is decided by the forward voltage difference of the diodes 12, 13 produced by the current ratio set between the semiconductor device.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a waveform shaping circuit that converts an input signal to be processed into a rectangular wave and a 2/.-Schmitt circuit used for chattering prevention.

Conventional configuration and its problems A Schmitt circuit has two intermittent states depending on the level of an input signal, and the level point that changes intermittently is called a Schmitt level.

Various types of Schmitt circuits have been put into practical use, but in many cases the Schmitt level is set by a resistance ratio. By the way, when a Schmitt circuit is implemented as a semiconductor integrated circuit, there is a disadvantage that the Schmitt level (2) is affected by variations in resistance ratio, temperature characteristics, and the like.

OBJECTS OF THE INVENTION The present invention has been made in order to eliminate the above-mentioned disadvantages, and has an object to provide a Schmitt circuit which has a simple circuit configuration and can obtain a Schmidt level with high accuracy.

Structure of the Invention The present invention provides an input signal to be processed, an amplifier with a common emitter connection type in which the input signal to be processed is applied to one base, and a plurality of semiconductor devices each connected to the base of the amplifier and having diode operation. a DC voltage source that supplies a forward bias to the base of the amplifier and the previous ljL semiconductor device; and a DC voltage source that is disposed between the connection path between the base of the amplifier and the semiconductor device, and that A Schmidts circuit consisting of a current source circuit that provides a predetermined current ratio and controls the current flowing through the semiconductor device in response to the operation of the amplifier, derivation means for extracting an output signal, and a signal output terminal. , whose Schmidt level is
It is determined by the forward voltage difference of the diode caused by the current ratio set between the semiconductor devices.

DESCRIPTION OF THE EMBODIMENT FIG. 1 shows an embodiment of the present invention. In FIG. 1, transistors 3 and 4 form a differential amplifier to which load transistors 1 and 2 are connected. Furthermore, the base potential of transistors 3 and 4 is connected to the diode 12.1.
It is determined by the potential of the cathode in step 3. Diode 12.1
The anodes of diodes 12 and 13 are commonly connected and connected to the bias power supply 26 at a predetermined potential v2.
The potential of the cathode of is determined by the current flowing through each diode.

Transistor 6, 2 and transistor 9, 10.1
1 constitute a Karen mirror circuit.

In this embodiment, the emitter current of transistor 9 is set to 11. The emitter current of transistor 10 is 12. Emitter current of transistor 11: Collector current of transistor 6.7 in conduction state: Current flowing through diode 12. shall be.

T and the above current I,, I2. I. The current ratio of:
I2:l3=2Io=4techniques. :3 construction.・・・・・・(1
) will be described in detail below using FIGS. 1 and 2.

In FIG. 2, a represents the input signal vIN waveform input to the base of the transistor 30 via the signal input terminal 27, and b
is the 4 waveform generated at the base of the transistor 4, and C is the 2 waveform which shows the collector potential of the signal output terminal 28, that is, the transistor 8. The horizontal axis shows time and the vertical axis shows the potential.

Between the anode and cathode of diode 12.13 57.
・・・Respectively the voltage between ■12. v13, do 12,1
The difference in potential between the cathodes of transistors 3 and 4, that is, the difference in potential between the bases of transistors 3 and 4 of the differential amplifier is . depends only on the ratio of

In FIG. 2, time t. Now, let us consider that the DC potential v3 of the transistor 3 of the input signal N is 61. . . . At this time, the transistor 3 is cut off. If transistor 3 is cut off,
Transistor 5 is also cut off, and current flows through transistors 6, 7 and 11, respectively. Therefore, the current I4 flowing through the diode 12 is given by equation 1: I4 ``I2 ''3 Old... (6) =
I.

At this time, the current flowing through the diode 13 is I, =2
I.

Therefore, the forward voltage difference ΔV between the diode 12 and the diode 13 is expressed by equation 4: = −I n 2
(○ A... From formula 7 (A), the base potential v4 of the transistor 4 becomes .

At this time, if the value R22 of the resistor 22 is selected so that the L-transistor 8 is conductive and the transistor 8 is not saturated, the potential VOUT of the signal output terminal 28 becomes I3×R22.

At this time, the base potential of the transistor 3 becomes equal to the base potential v4 of the transistor 4, and immediately after t, the transistor 3 becomes conductive and the transistor 4 is cut off. When the transistor 3 is conductive, the transistor 5 is also conductive, and the transistors 6, 7 and 8 are cut off.・・・・・・(8)4
It becomes 20. At this time, the current flowing through the diode 13 is ■1-
21o, so from equation 4, the above dV is = βn
2) O...(9) becomes lower. At this time, the transistor 8 is also cut off, and the potential of the signal output terminal vOUT
is zero volts or less, time t2. t3. Also at t4...
The conduction state of transistor 3 and transistor 4 is switched, and an output waveform as shown in FIG. 2(C) can be obtained.

In this example, I, :I2:I. = 2I0: 4 engineering. :3I0, but by arbitrarily setting this current ratio, a desired Schmidt level can be arbitrarily selected. That is, according to the Schmitt circuit of the present invention, 11. I2
．． If the relative ratio of I3 is taken, the Schmidt level is
It is determined only by Equation 4.

Further, in the present invention, the number of diodes 12 and 13 in the semiconductor device that determines the Schmidt level is not limited to a single number, and it is extremely easy to arrange any number of diodes 12 and 13. It is obvious to those skilled in the art that the Schmitt level in this case is multiplied by the set level selected for the above-mentioned current ratio by the number of diodes in the semiconductor device.

Effects of the Invention As mentioned above, the Schmitt circuit of the present invention, especially its Schmitt level, is set in the above-mentioned current source circuit based on a relatively small reference level of - (approximately 26 mV at room temperature). Since the current ratio is multiplied and determined, it is particularly suitable for obtaining a relatively small Schmidt level.

Furthermore, if the Schmitt circuit of the present invention is implemented as a semiconductor integrated circuit, the above-mentioned current source circuit, semiconductor device having diode operation, and differential amplifier with a common emitter connection type can be constructed with high precision, and the 101' effect of the present invention is further enhanced. I feel encouraged.

[Brief explanation of drawings]

Fig. 1 is a circuit diagram of a Schmitt circuit according to an embodiment of the present invention, and Fig. 2 (a, c, (b), CC) shows the input signal waveform (VIN) of the Schmitt circuit, the bias of the differential amplifier, respectively. Waveform (v4), and output signal waveform (■0
FIG. 1-11...transistor, 12-13...
... Diode, 14-22 ... Resistor, 23
... Constant current source circuit, 24-26 ... Bias power supply, 26 ... Capacity, 27 ...
・Signal input terminal, 28...Signal output terminal, 29
・・・・・・Power terminal. Name of agent: Patent attorney Toshio Nakao and 1 other person No. 1
Figure 1. l2I3 @ 2 Ward

Claims (1)

[Claims] an input signal to be processed; an amplifier with a common emitter connection type to which the input signal to be processed is applied to one base; a plurality of semiconductor devices each connected to the base of the amplifier and having diode operation; and a base of the amplifier. A direct current voltage source that supplies a forward bias to the semiconductor device and a connection path between the base of the amplifier and the semiconductor device, the DC voltage source providing a predetermined current ratio between the plurality of semiconductor devices, and the A Schmitt circuit comprising a current source circuit that controls the current flowing through the semiconductor device in response to the operation of an amplifier, deriving means for extracting an output signal, and a signal output terminal.