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AP3302 Pt3 Contents

AP3302 Pt3 Section 2Contents

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AP 3302 Pt. 3

Section 2

CHAPTER 5

Clamping Circuits

This restoration of the d.c. component is done by clamping circuits (d.c. restorers) although, as we have seen, the clamping circuit may be adjusted such that the output waveform varies about any selected level, not merely the d.c. level of the input signal.

It may be thought that the necessary d.c. component could be added by using a bias circuit. A fixed d.c. voltage is not suitable however because it is necessary to arrange for the d.c. component to alter automatically as the amplitude or pulse duty factor of the input alters. As we shall see later a clamping circuit will give the required variation.

Basic Clamping Circuit

A clamping circuit consists simply of a long CR circuit in which the resistor is shunted by a thermionic or semiconductor diode. The direction of connection of the diode in the circuit decides the direction of clamping. Fig 3 shows a basic clamping circuit and also the conditions existing when the diode is cut off and when it is conducting. When the diode is cut off, R is shunted by the very high impedance of the non-conducting diode and the effective resistance is R, in this example 1MW.


 

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