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AP3302 Pt3 Contents

AP3302 Pt3 Section 2Contents

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AP 3302 Pt. 3

Section 2


Clamping Circuits

Applications of Clamping Circuits

Clamping circuits have many uses in radar. The following paragraphs consider a few examples.

a. Pulse shaping. In Chapter 4 (p 88) we saw that the output from a triode squarer is not a perfect square wave. It can however be made more square by other circuits. We often need to 'tidy up' a waveform in this way and the process is known as pulse shaping, and may include both limiting and clamping. Fig 11 shows an example. The output from the squarer varies between + 200V and + 300V and is considerably curved below the + 225V level. This waveform is positively clamped to - 25V so that the curved portion is negative with respect to earth (zero volts) and the remainder is positive. The clamped waveform is then negatively limited to zero volts so that the curved portion is cut off and we are left with a good square wave of 75V amplitude, positive-going with respect to earth.

b. CRT blanking pulse. A blanking pulse is normally applied to the grid of a c.r.t. to cut off the electron beam during the resting time between traces. The required input Vg to the grid of the c.r.t. is shown in Fig 12b, where VT is the level of voltage needed during the trace to give the required brightness.


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