What is the difference between comparator and schmitt trigger

Modern operational amplifiers that serve as comparators are presented as independent integrated circuits ICs , designed by many manufacturers. Figure 1. Open-loop operational amplifier a and an operational amplifier as a comparator b. Figure 3.

Comparator with reference voltage input and output characteristics. Figure 4. Comparator with reference voltage and a Zenner diode circuit. One of the very frequent operational amplifier applications is detecting if the input voltage is reaching a certain threshold voltage level.

In this case the operational amplifier is used in the circuit depicted in Figure 5, and this circuit is called the Schmidt trigger.

If we need the switching level to be other than 0, we must add a reference voltage to the scheme as shown in Figure 6. Figure 5. Schmidt trigger circuit.

Figure 6. Schmidt trigger with reference voltage. The operational amplifier can also perform timing functions. For this purpose, the operational amplifier can be used in the circuit shown in Figure 7, and is called a multivibrator. This circuit is generating the square signal with a fixed period and amplitude.

Figure 7. Multi-vibrator circuit. You must be logged in to post a comment. Figure 2. Add to Add to collection s Add to saved. Craig 3 — The comparator is perhaps the simplest form on an analog-to-digital converter, i.

The comparator output consists of only two discrete levels. Craig 4 — It is possible to construct an inverting comparator by connecting the non-inverting terminal to ground and connecting the input to the inverting terminal. Comparator and Schmidt Trigger K. Craig 6 — Below is the waveform of a comparator with a reference voltage of 0. Craig 7 — Another useful interpretation of the op-amp comparator can be obtained by considering its inputoutput transfer characteristic.

Craig 8 — Shown below is the transfer characteristic for a comparator of the inverting type with a nonzero reference voltage. Commonly used voltage levels in this type of switching circuit are 0 and 5V. These typically can accept relatively large inputs and have provision for selecting the desired reference voltage levels. The open-collector output allows the user to connect the output transistor to any supply voltage of choice by means of an external pull-up resistor, thus completing the output circuit.

Craig 10 — The actual value of the resistor is not critical, since the transistor is operated in the saturation mode; values between a few hundred and a few thousand ohms are typical. The desired threshold is then represented by a DC reference Vref connected to the non-inverting input, and the input voltage source is connected to the inverting input.

Craig 12 Comparator Response to Noisy Inputs — One very effective way of improving the performance of the comparator is by introducing positive feedback. Positive feedback can increase the switching speed of the comparator and provide noise immunity at the same time.

Transfer Characteristic of the Schmitt Trigger Can you explain how this works? Craig 14 — If it is desired to switch about a voltage other than zero, a reference voltage can also be connected to the non-inverting terminal.

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