DIODE CIRCUITS 



CLAMPING 



This is a form of electronic switch for suppressing a signal electronically for 

 the duration of a pulse generated elsewhere. As for the catchers and clippers 

 we have a generator feeding a load resistance, which is large, via R. The 

 diodes are connected to a pulse transformer with a centre-tapped secondary, 

 whose primary is fed from the switching pulse generator (Figure 6.40). 



R 

 -AAA 



Figure 6.40 



In Figure 6.41a we have the pulse generator output and in b the pulse 

 transformer output. Between pulses the polarity is such as to bias the diodes 

 in the high resistance direction and the signal passes through to the load. 



(a) 



-=A 



A=J:l^^ 



(b) 



(c) 



Figure 6.41 



On the arrival of the pulses the diode bias reverses, changing them to low 

 resistance, so that the signal output is attenuated as shown in Figure 6.41c. 

 The attenuation produced during the clamp period with an ideal pulse 

 transformer is 



2 ^4«2 



D.C. RESTORING 



Suppose we have a generator feeding a high-pass filter of the simplest kind 

 as shown in Figure 6.42, and suppose the waveform of the generator is a 

 train of 'saw-teeth'. This train might have the form of Figure 6.43a, where 

 the output moves between +2 'ind — | K, or b, where it is between and + V, 



112 



