- Schmitt Gates Defined: A Schmitt Gate is a type of logic gate that employs two separate threshold voltages to handle transitions, enhancing stability and reducing noise.
- Hysteresis Function: The unique feature of Schmitt Gates is hysteresis, a mechanism that allows them to maintain output stability against noisy signals.
- Circuit Symbols: Circuit symbols for Schmitt NAND and Schmitt inverter gates help differentiate them from conventional logic gates.
- Comparison to Conventional Gates: Unlike standard gates, Schmitt Gates operate on the principle of hysteresis, similar to the B-H loop in ferromagnetic materials.
- Practical Application: Schmitt Gates are crucial in electronic circuits where signal stability is essential, particularly in environments with high electrical noise.
We have discussed various types of logic gates, finally we are going to discuss about another type of gate that is Schmitt Gates. The logic gates about which we have discussed till now have a single input threshold voltage level. For low to high and high to low output transitions this threshold is the same and it lies somewhere between the highest low voltage level and the lowest high voltage level. And for this these logic gates might produce an erratic output which when fed with an input which is varying slowly.
Consider an ideal input signal given to an inverter circuit; the response is illustrated in the graph below.
When a practical signal is applied, the resulting response is depicted in the subsequent figure.
The diagram above reveals that a small amount of noise is superimposed on the output signal. A possible solution to this problem is to differentiate the voltage levels for low-to-high and high-to-low transitions.
This is achieved by introducing positive feedback within the gate circuitry, a process known as the hysteresis phenomenon. There are some logic gates which are naturally have hysteresis i.e. they have this property as built in, we don’t have to change the manufacturing procedure for them.
This is mainly seen in NAND gates and inverters. These are known as Schmitt gates and they are capable of interpreting input voltage according to two threshold voltage which is for low to high and the other one is for high to low output transition. The (a) and (b) figures below shows the circuit symbols of Schmitt NAND and Schmitt inverter.
The difference between Schmitt gates and conventional gates are that the former have the hysteresis nature which is identical to the B-H loop for a ferromagnetic material.
The figure above shows the typical characteristics of transfer of such a device. The difference which we can see between the two threshold levels is the hysteresis. The next figure shows the characteristics of a Schmitt inverter to a slowly varying noisy input signal.
