JPS61205017A - Schmitt trigger circuit - Google Patents

Abstract

PURPOSE:To obtain the stable hysteresis width and to attain a Schmitt trigger circuit which can be converted advantageously into an IC, by performing the changeover between the upper and lower limit potentials with the changeover between the active and cut-off states of a transistor. CONSTITUTION:Transistors TR Q2 and Q3 form a differential circuit, and a common emitter is connected to a constant current source 1. The base of the TR Q2 is connected to a terminal 2 via a resistance R1 and also to the collector of a TR Q1. The base of the TR Q3 is connected to an input terminal 4 with the collector connected to the emitter of the TR Q1 and also grounded via a resistance R2. The base of the TR Q1 is connected to a terminal 3 and the collector of the TR Q2 is connected to an output terminal 5. The reference voltages Vref1 and Vref2 are applied to terminals 2 and 3 respectively. The Vref1 is higher than the Vref2.

Description

[Detailed Description of the Invention] [Field of Industrial Application] The present invention relates to a hysteresis circuit, which exhibits constant and stable hysteresis characteristics regardless of pressure fluctuations, and is suitable for use in integrated circuits. ) Regarding the l-Riga circuit.

[Conventional technology]

An example of a conventional hysteresis circuit is shown in FIG. Resistors R6, R7 and R8 are connected in series between the trace source terminal 7 and the tangential surface. Transistors Q5 and Q6 forming a differential
are connected to a constant IE a source 9 with their emitters connected in common. The base of the transistor Q5 is connected to the connection point between the resistors R6 and R7, and the collector is connected to the output terminal 5. The base of the transistor Q6 is connected to the long terminal 4, and the collector is connected to the connection point between the resistors R7 and R8.

In the initial state where the transistor Q6 is in the cutoff state and the transistor Q5 is in the active state, the base potential vL of the transistor Q5 is given by (Equation 13).

Here, Vcc is the "power supply" voltage applied to the power supply terminal 7. As shown by the arrow, when the transistor Q6 is in the active state and the transistor Q5 is in the suspended state, the base potential vI of the transistor Q5 is determined as follows.

Vcc= (Ra+Ry)・It+Re(11+
I2)... (2) VH"R7・Il+Rs・(I!+I2)... (
3) Here, 11 is the current flowing through the resistors R61R7,
The same 'Wt current also flows through resistor R8. 12 is an mc current supplied from the collector of the transistor Q6 to the resistor R8, and assuming that the current amplification factor of the transistor Q6 is sufficiently large, it is equal to the current value IC3 of the current source 9, and I2 in I2.
According to equations (2) and (3), cs becomes cs.

It has a Schmitt trigger lower limit voltage and upper limit voltage given by Equation 4.

[Problem that the invention seeks to solve]

In the conventional Shemitt trigger circuit described above, the upper steresis width H is given by (1), (H2vH-vL from the equation 4J. As shown in the equation (5), the hysteresis width H
It is determined by the Fi resistance value and constant current value. In particular, it is greatly affected by variations in the resistance value of the resistor R8, and is also affected by the temperature characteristics and power supply voltage dependence of the constant current value.

SUMMARY OF THE INVENTION An object of the present invention is to provide a Shemitt trigger circuit which improves the conventional problems, exhibits stable hysteresis characteristics, and is suitable for integration into an integrated circuit.

[Means for solving problems]

According to the present invention, @1. a differential circuit having a second input terminal and a first second output terminal; a first reference potential terminal connected to the first input terminal via a first resistor; a transistor connected to the first input terminal, a second reference potential terminal connected to the base, and a second resistor connected to the emitter, and the first output terminal of the differential circuit is connected to the emitter of the transistor. Connect this transistor to
A Shemite trigger circuit is obtained which controls the interruption and provides an output from a second output in response to an input signal applied to a first input.

〔Example〕

Next, the present invention will be explained with reference to the drawings.

FIG. 1 is a circuit diagram showing an embodiment of the present invention. Transistors Qz and Qs constitute a differential circuit, and the common emitter is a constant 11! c is connected to the flow source 1. Transistor Q2
The base of is connected to terminal 2 via resistor R1, and also to the collector of transistor Ql. The base of the transistor Q3 is connected to the input terminal 4, the collector is connected to the emitter of the transistor Ql, and is grounded via a resistor R2. transistor Q
The base of transistor Q2 is connected to terminal 3, and the collector of transistor Q2 is connected to output terminal 5. A reference voltage VrefltVref2 is applied to the terminals 2 and 3, respectively,
The reference voltage Vref1 is set at a higher level than the reference voltage Vrefz.

In the initial state where transistor Q2 is in the active state and transistor Q3 is in the suspended state, the collector 11L current ICI of transistor Q1 is given by, and therefore the base 11L current ICI of transistor Q2 is given by V.
It is given by the L'rii force formula.

Here, VBEqxld is the forward bias potential of transistor 1.

Next, transistor Q2 is in the cutoff state, transistor Q
When Q3 becomes active, the base potential ■H' of the transistor Q2 is determined as shown in equation (9) below. In other words,
Due to the activation of the transistor Q3, the constant current Ics of the constant current source 1 is supplied to the resistor R2, and a potential of VH2''IC3' R1 is generated across the resistor R2. It is assumed that the current amplification factor is sufficiently large.

Next, Vrefz Vagqx < Viz 6−°0(
By arbitrarily setting the constant current Ics and the resistor R2 so as to satisfy the condition 8), the transistor Ql is brought into an interrupted state. Therefore, the base potential v of transistor Q2
H' is determined by the reference potential Vrefx, and VH'=V
ret+ ' `` '''(9', and the hysteresis width H' is (7J, according to the tsH formula, H' = ■
H'-■L', as shown, the reference voltage Vrefx and constant '1 current I
Regardless of the value of C3, it can be set by the level drop of the collector current of transistor Q1 across resistor R1. Moreover, the reference voltage Vrefz is set to the transistor Qt,
By making the forward bias potential vagqt have a voltage fluctuation that compensates for the fluctuation due to temperature change, it is possible to set it only by the relative ratio of resistors R1 and R2.
- In integrated circuits, it is difficult to suppress variations in the resistance values of the resistors themselves and fluctuations due to temperature characteristics, but it is easy to keep the ratio of resistance values constant. Therefore, the hysteresis width can be obtained with high accuracy by integrating the circuit.

FIG. 2 shows another embodiment according to the present invention. In this case, the transistor Ql of the embodiment shown in the IT diagram has a current mirror configuration, and a constant voltage is obtained by a constant voltage source 6, a forward biased diode D1, and a resistor Rs. A resistor R2 is connected to the bases of transistors Ql and Q4, and a resistor R2 is connected to the emitter of transistor Q1.
In addition, a resistor 1<5 is connected to the emitter of the transistor Q4, and a resistor R4 and the base of the transistor Q2 are connected to the common collector of the transistors Ql and Q4. Shiemit trigger lower U-4 pressure VL
", upper limit voltage V, ", and hysteresis width H" are obtained in the same manner as described above, and are (11), (12), respectively.
(13) is given by Eq. .

VL'=VCC-R4' (IC4+ICI)
...(11) VH=Vcc-R4・IC4”・(12
)H'=VH'V L''=l(□m K4 (13) Here, IC1lIC4# is the collector current of the transistors Ql-Q4.

'p, In Figure 2, the collector 1 current IC1 is a current mirror circuit number consisting of a diode Dl + transistor Q and a resistor ks * Rz. Since it is obtained as rttt, the hysteresis width H is determined by the constant current source 6 and the resistor R4.
, and is unaffected by other 'IL source pressures and constant 'wt flow source 1 values. In addition, as mentioned above, the constant current value Ics of the constant current source 1 may be sufficient as long as the g current is sufficient to cut off the transistor (Jl) at times. If a direct voltage is given, all transistors in this circuit operate in non-saturation, so high-speed operation is possible.

'f: The hysteresis width H' is affected by the variation in the resistance value of the resistor R4, but the shadow 1 of this variation in resistance value is
However, the influence of this variation in resistance value is not as large as in the conventional case.

〔Effect of the invention〕

As explained above, according to the present invention, in a shemit trigger circuit, stable hysteresis can be obtained by switching between the upper limit potential V and the lower limit potential VL by switching between the active state and the cutoff state of the transistor. In addition, it is possible to obtain a circuit that is advantageous for integration.

[Brief explanation of the drawing]

FIG. 1 is a circuit diagram showing one embodiment of the present invention, FIG. 2 is a circuit diagram showing another embodiment of the invention, and FIG. 3 is a circuit diagram showing a conventional Shemite trigger circuit. . 1.6.9... Constant current source, 2,3...
Terminal, 4...Input terminal, 5...Output terminal, 7...Power terminal, Q1 to Q6...
Transistor, R1~R,... Resistor, Dl...
····diode.

Claims (1)

[Claims] a differential circuit having a first input terminal, a second input terminal to which an input signal is applied, and first and second output terminals; a first resistor at the first input terminal of the differential circuit; a transistor whose collector is connected to the first input terminal, whose base is connected to a second reference potential terminal, and whose emitter is connected to a second resistor; the first output terminal is connected to the emitter of the transistor to control conduction/cutoff of the transistor;
A Schmitt trigger circuit characterized in that an output signal is taken out from the second output terminal.