Voltage Comparator Principle

The voltage comparator is an integrated operational amplifier nonlinear application circuit, which is often used in various electronic devices. So what is a voltage comparator? Let me introduce it to you. It compares an analog voltage signal with a reference fixed voltage. When the amplitudes of the two are equal, the output voltage will jump and the corresponding output is high or low. The comparator can form a non-sinusoidal waveform conversion circuit and be used in the fields of analog and digital signal conversion.

Figure 1 shows the simplest voltage comparator. UR is the reference voltage, which is added to the non-inverting input terminal of the operational amplifier, and the input voltage ui is added to the inverting input terminal.

(a) Circuit diagram (b) Transfer characteristics When ui＜UR, the op amp outputs a high level, and the voltage regulator Dz works in reverse regulation. The output potential is clamped at the voltage regulator's stable voltage UZ, that is, uO＝UZ

When ui＞UR, the op amp outputs a low level, DZ is forward-conducted, and the output voltage is equal to the forward voltage drop UD of the voltage regulator tube, that is, uo＝－UD

Therefore, with UR as the boundary, when the input voltage ui changes, the output end reflects two states, high potential and low potential.

The characteristic curve that shows the relationship between the output voltage and the input voltage is called the transfer characteristic. Figure 3-1(b) shows the transfer characteristic of the comparator in Figure (a).

Commonly used voltage comparators include zero-crossing voltage comparator, zero-crossing comparator with hysteresis characteristics, hysteresis voltage comparator, and window (double limit) voltage comparator. LM339 is often used to form various voltage comparators.

Integrated voltage comparator introduction:

Function: It can convert analog signals into binary signals, that is, discrete signals with only two states: high level and low level.
Application: As an interface circuit between analog circuits and digital circuits.
Features: It has lower open-loop gain than integrated operational amplifiers, larger offset voltage, and smaller common-mode rejection ratio; but it has faster response speed, shorter transmission delay time, and can directly drive integrated digital circuits such as TTL, CMOS, and ECL without an external limiting circuit; some chips have strong load carrying capacity and can also directly drive relays and indicator lights.