JPS61263305A - Hysteresis comparator - Google Patents

Abstract

PURPOSE:To set optionally the temperature coefficient of hysteresis width by switching a current source current of each emitter so as to change the potential difference of the resistor between both emitter terminals of a transistor (TR) pair constituting a differential amplifier. CONSTITUTION:In a hysteresis comparator, when differential input voltages V1, V2 have a relation of V1>V2, TRs Q13, Q14, Q15 are turned off and a current source Iphi3 is set. When the voltage V1 is small and collector currents (Ic) of TRs Q11, Q12 are nearly equal, the circuit is inverted and the current is nearly equal to (Iphi1+Iphi2+Iphi3)/2. A current of (Iphi1+Iphi3-Iphi2)/2 flows to a resistor R1 and an offset by said current is given. When the voltage V1 is large and the output is switched conversely, an offset of (Iphi1-Iphi2)/2.R1 is given. The potential difference of the offset gives a hysteresis width. In this case, since the current source Iphi3 is decided by a voltage drop of the resistor R1, the temperature coefficient of the hysteresis width is set optionally.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a hysteresis comparator having a differential input waveform shaping function.

Conventional Technology For example, a differential input comparator with hysteresis used in a position signal processing means using a Hall element, such as in a motor control system, has a differential input voltage level of 100 m.
Since the value is around V, the hysteresis voltage width is also 10~
It is as small as somV.

To set such a small hysteresis voltage width,
The difference in base-emitter voltage of a differential amplifier stage based on the emitter area ratio and current density ratio of differential pair transistors is often set as the hysteresis voltage width.

FIG. 2 is a circuit diagram of a typical conventional hysteresis comparator, and an outline of the circuit operation will be explained below. Transistor Q1. Q2. The emitter area ratio of Q3 is SEl
i SE2 iS), 3”1 i 1 in. If each differential input voltage v1.■2 is v2>vl, then
transistor Q is on, transistor Q2. Since Q3 is turned off, the current mirror pair of transistors Q4. Through Q6,
Transistor Q6 is off, diode D is on, and when v2 becomes small, cholera current IC3
When +Ic2=IC1, transistor Q6 turns on. Conversely, when the voltage v2<vl, the transistor Q6 is on and the diode D is off, and when v2 becomes large, when the collector current C2=C1, the transistor Q6 turns off and the output is switched.

Therefore, the hysteresis voltage width VH varies between transistors Q2 and Q3. Q2 (however, Q3+Q
2) and is determined by the emitter area ratio, and is expressed as in equation (1).

T VH=-1n(n-H) -------・-(
1) (where q; electronic charge k; Bolmar constant T;
Temperature) For example, if n=1, from equation (1), a hysteresis voltage width of about 18 mV can be set at room temperature.

Problems to be Solved by the Invention However, in the case of a hysteresis comparator as shown in FIG. 2, the hysteresis voltage width has a temperature coefficient, as is clear from equation (1). Particularly when applied to motor control devices, this hysteresis comparator may be integrated on the same chip as the power transistor.
The temperature range to be guaranteed is wide, and if the Hall element input signal is minute, the setting of the hysteresis voltage width becomes difficult.

In addition, in the case of a hysteresis comparator as shown in Fig. 2, the differential input condition is vl (v2 and vl>v2
In the case of the transistor Q side and the same Q2 side at the same voltage difference. Since the base current value on the Q3 side differs by a factor of (n+1), if the signal source impedance of the differential input is not low enough, the differential input, which was originally completely symmetrical, becomes asymmetrical. This may become a problem when applied to a motor control device, for example, and when a differential input signal is used in an integrated circuit other than a hysteresis comparator.

The present invention provides a circuit configuration that can eliminate such problems.

Means for Solving the Problems In summary, the present invention consists of a pair of transistors constituting a differential amplifier, a resistor connected between both emitter terminals of the pair of transistors, and a current flowing through each emitter terminal of the pair of transistors. The hysteresis comparator is configured such that a current source is connected to one of the current sources, the current source current is switched by a transistor controlled by the output of the differential amplifier, and a hysteresis width is set by a potential difference generated in the resistor.

According to the present invention, a pair of transistors constituting a differential amplification stage, a resistor connected between the emitter terminals of the pair of transistors, a pair of current sources connected to the emitter terminals of the pair of transistors, and a current flowing through one of them. Since the second pair of current mirrors that can be turned on and off are connected in parallel to the source, the hysteresis width is determined by the current of the second pair of switchable current mirrors and the voltage drop generated in the resistor. Therefore, it is easy to set the temperature coefficient.

In addition, the base currents of the transistor pairs that make up the differential amplifier stage are symmetrical because current changes are small.

The impact is small.

Embodiment FIG. 1 shows a circuit configuration of a hysteresis comparator according to an embodiment of the present invention.

The circuit operation will be explained below. The differential input condition is vl〉■2
When transistor Q13. Q14. Q1. is off,
Transistor Q16. A current source Iφ3 formed by a pair of current mirrors made up of Q1□ is on.

Therefore, vl becomes smaller and transistor Q
13. Q14. Q1. is turned on because the differential pair transistor Q11. This is when the collector currents of Q12 are approximately equal, so the current value is
It is approximately equal to Iφ3)/2.

Therefore, the resistance R1 has (Iφ1 + engineeringφ3−Iφ2
)/2 current is flowing, and an offset (potential difference) equal to (Iφ1 + engineeringφ3−Iφ2)/2・R4 is flowing between both emitters.Conversely, if the differential input condition is v2>vl, When, transistor Q13.Q14.Q
1° is on and current source Iφ3 is off. Therefore, the reason why vl increases and the output switches is due to the transistor pair Q11. This is when the collector current of Q1□ is approximately equal, that is, approximately equal to (Iφ1+φ2)/2, and a current of (φ1−I)/2 is flowing through the resistor R1. At this time, transistor Q11. Q12
An offset of (Iφ1-Iφ2)/2·R1 is created between the two transmitters, and this potential difference becomes the hysteresis width. Note that the transistor Q18. Q19 is a pair of current mirrors for the current source.

From the above, the total hysteresis width is the sum of the offsets of the above two states, that is, as the current source Iφ3 is determined by the voltage drop across the resistor R1, There is an advantage that the temperature coefficient of the hysteresis width can be set arbitrarily.

Furthermore, since the change in pace current is smaller than in the past, the signal will not be distorted even if the signal source impedance is high.

Effects of the Invention As is clear from the above, the present invention has the following two effects.

The first effect is that the temperature coefficient of the hysteresis width can be set arbitrarily.

The second effect is that even input signals with high signal source impedance are not distorted.

[Brief explanation of drawings]

FIG. 1 is a circuit diagram of a hysteresis comparator according to an embodiment of the present invention, and FIG. 2 is a circuit diagram of a conventional hysteresis comparator. Q11-Q19...Transistor, R1...
···resistance.

Claims (1)

[Claims] A transistor pair constituting a differential amplifier, a resistor connected between both emitter terminals of the transistor pair, and a current source connected to each emitter terminal of the transistor pair, and one of the current sources is connected to the differential amplifier. A hysteresis comparator configured to switch a current source current using a transistor controlled by an output of a dynamic amplifier to set a hysteresis width based on a voltage difference generated across the resistor.