JPS61156915A - Threshold value switching circuit - Google Patents

Abstract

PURPOSE:To attain threshold switching setting with high accuracy by using two transistors (TRs) having an identical characteristic to switch the threshold value and controlling the setting of threshold value with high accuracy by a resistor and a reference power supply independently of the saturated voltage of the TRs. CONSTITUTION:An input voltage is applied to a non-inverting input of a comparator OP1, the comparator OP1 compares the input voltage VIN with an inverting input voltage Vth and outputs the result as a voltage Vout. Then a current of an input TRQ3 of a current mirror comprising the TRs Q3, Q4 connected to the output is controlled to allow the output TRQ4 to control a TRQ0 in the threshold switching TRs Q1, Q0 to actuate the TRQ1 for the threshold value change. It is possible to decrease the setting error from nearly 10% of a conventional threshold value switching using a low reference voltage into an error of 1% or below by providing the paired TRs for the threshold value switching. Thus, the comparison with high accuracy is attained even when the reference voltage is low without being affected by the saturated voltage of the TRs.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a signal detection circuit having hysteresis characteristics by threshold switching.

(Prior Art) A conventional detection circuit with hysteresis has a configuration as shown in FIG. 7, and an example of the comparator circuit used is shown in FIG.
TA BOOK, Industrial Linear IC, Interface IC, page 789, page 831 Hitachi Catalog).

The circuit shown in FIG. 7 has an output of V. ut is low level (=OV
) to high level (Vcc)
The condition for input voltage is expressed by equation (1), and the input voltage condition for transition from a high level to a low level is expressed by equation (2).

Here, in equation (1), Yout is the saturation voltage of the transistor Q shown in FIG. 8, and if approximately set to zero, then (
The two threshold values shown by equation 11(2) are determined by the power supply voltage VCC, which is a reference power supply, and the resistance.

(Problem to be solved by the invention) However, when VCC is low and threshold accuracy is required, the above value is approximately zero (Vou in equation 11).
t, that is, the influence of the saturation voltage of Q8 in FIG. 8 cannot be ignored. That is, the saturation voltage of a transistor varies from several mV to about 500 mV depending on the collector current temperature and the like.

Therefore, if R, -R3 and Vcc 5V, the maximum is 10
However, this method has the drawback that it is difficult to set a highly accurate threshold value due to the occurrence of errors of the order of magnitude.

Therefore, an object of the present invention is to obtain a circuit that can perform highly accurate threshold switching settings using a circuit configuration suitable for integrated circuits.

(Means for Solving the Problems) A feature of the present invention is that threshold switching is performed using two transistors having the same characteristics that can be easily obtained by integrating them for threshold switching, and that the threshold setting is different from that of the transistor. The advantage is that it can be set accurately using a resistor and a reference power supply, regardless of the saturation voltage, etc.

(Function) With the above configuration, the threshold voltage is obtained by dividing the reference voltage by resistance, and a pair of transistors with the same characteristics is used for the threshold selection switch, so the reference voltage can be adjusted without being affected by the saturation voltage of the transistor. Accurate comparisons can be made even when the

(Example) FIG. 1 shows a first embodiment of the invention.

An input voltage is applied to the positive phase terminal of the comparator OPl,
Comparator OPl compares input voltage VIN and negative phase terminal voltage Vth, outputs the result as voltage Vout, and simultaneously outputs the result from transistor Q3. The output transistor Q4 is a transistor Q for threshold switching. Q of r Ql.

As a result, Q is operated and the threshold value is changed. Comparison voltage Vth with respect to input voltage VIN, output voltage V
The waveform of out is shown in FIG. That is, the output changes with respect to VIN under the following conditions.

Equation (3) is when Vout changes from a high level to a low level, and Equation (4) is when Vout changes from a high level to a low level. This is the case when ut changes from a low level to a high level. Here, ΔVBE is the transistor Q. rQl 0 is the base-emitter voltage difference, and if each collector current is IC0T IC+, it is expressed by equation (5).

rso j F transistor Q. Reverse saturation current ■s1
;Reverse saturation current of transistor Q1■T=Wataru("26
mV) Ta=2b℃K; Boltzmann's constant q; electron charge T; absolute temperature ds. , ■s is a transistor Q. , Ql have the same shape and the same process conditions, they are almost the same and can be easily realized by integrated circuits.

Therefore, transistor Q. The collector current ratio of jQI is 2
Even if the difference is about a factor of two, if we take ISO''ISI from equation (5), ΔVBE-=26X10-36m(2):18XlO-
”(V) (Ta=25°C), and the degree of influence on equation (4) as an error is VEE=5V R2=FL3
Even so, it is about 0.4 q6 and can be almost ignored. If the comparator OP1 has the configuration shown in FIG. 2, the transistors Q3. Q is unnecessary, and can instead be constructed with a PNP transistor Q2 having a double collector, which is easy to use in an integrated circuit.

FIG. 4 shows a configuration example for a positive input signal.

PNP transistor pair Q as threshold switching transistors. , Ql, and the transistor Q. A current mirror circuit consisting of transistors Q, , Q, is added for driving. The operating voltage at each point with respect to the input VIN is the fifth
As shown in the figure. Also, the threshold value can be set by changing -VEE in equation (3) (41) to +VCC.Similarly, transistor Q.+
By configuring Q+ with the same shape and the same process, it is possible to set it accurately.

Figure 6 shows current mirror transistor Q3+ Q4+
This is an example of a case where the comparator OPI is configured without using Q,,Q,.

(Effects of the Invention) As explained above, by providing a transistor pair for threshold switching, the setting error when using a low reference voltage during threshold switching can be reduced from about 10 in the conventional configuration to an error of 1 factor or less. Is possible.

Therefore, the present invention is highly effective when used in detection circuits having hysteresis that require high accuracy in threshold values and are used in locations where the reference power supply voltage used is low.

[Brief explanation of the drawing]

FIG. 4 is a diagram showing another embodiment of the present invention; FIG. 5 is a diagram showing voltage waveforms of the circuit in FIG. 4; FIG. 6 is a diagram showing voltage waveforms in the circuit shown in FIG. 4. Combare 0PIL%IYrk
7 is an example of a conventional hysteresis circuit, and FIG. 8 is an example of a comparator used in FIG. 7. OPl; Comparator V; Input terminal VOut z output terminal

Claims (1)

[Claims] In a signal detection circuit having a hysteresis characteristic that compares an input signal with a threshold value given by a resistance divider switchable by a switch of a reference voltage and outputs a comparison result, the switch is a pair of transistors whose bases are connected to each other. , the emitter of one transistor of the transistor pair is connected to the resistor providing the resistance division, the emitter of the other transistor of the transistor pair is connected to a reference potential, and the base and collector are connected to each other to provide an output of the signal detection circuit. A threshold switching circuit characterized in that it is controlled according to the following.