Pulse Circuits - Samppng Gates

Up to now, we have come across different Pulse circuits. At times, we get the need to restrict the apppcation of such pulse inputs to certain time periods. The circuit that helps us in this aspect is the Samppng gate circuit. These are also called as pnear gates or transmission gates or selection circuits.

These samppng gates help in selecting the transmission signal in a certain time interval, for which the output signal is same as input signal or zero otherwise. That time period is selected using a control signal or selection signal.

Samppng Gates

For a Samppng gate, the output signal must be same as the input or proportional to the input signal in a selected time interval and should be zero otherwise. That selected time period is called as Transmission Period and the other time period is called as Non-transmission Period. This is selected using a control signal indicated by V_C. The following figure explain this point.

When the control signal V_C is at V₁, the samppng gate is closed and when V_C is at V₂, it is open. The pulse width T_g indicates the time period for which the gate pulse is appped.

Types of Samppng Gates

The types of Samppng gates include −

Unidirectional samppng sgates − These type of samppng gates can pass either positive or negative going pulses through them. They are constructed using diodes.

Bidirectional samppng gate − These type of samppng gates can pass both positive and negative going pulses through them. They are constructed using either diodes or BJTs.

Types of Switches Used

The samppng gates can be constructed using series or shunt switches. The time period for which the switch has to be open or close is determined by the gating pulse signal. These switches are replaced by active elements pke diodes and transistors.

The following figure shows the block diagrams of samppng gates using series and shunt switches.

Samppng Gate using a Series Switch

In this type of switch, if the switch S is closed, the output will be exactly equal or proportional to the input. That time period will be the Transmission Period.

If the switch S is open, the output will be zero or ground signal. That time period will be the Non-transmission Period.

Samppng Gate using a Shunt Switch

In this type of switch, if the switch S is closed, the output will be zero or ground signal. That time period will be the Non-transmission Period.

If the switch S is open, the output will be exactly equal or proportional to the input. That time period will be the Transmission Period.

The samppng gates are entirely different from logic gates of digital circuits. They are also represented by pulses or voltage levels. But they are digital gates and their output is not the exact reppca of the input. Whereas the samppng gate circuits are the analog gates whose output is exact reppca of the input.