Q. With a suitable block circuit, show how linear sweep voltage is generated ?

The above figure shows a basic sweep waveform generator. The switching action of the switch causes the capacitor C to be alternately charged and discharged. The waveform generated by this basic circuit is not exactly linear, even if the ratio of the sweep voltage Vs and the supply voltage V is kept high. However, the linearity can be improved if feedback arrangement is made with this basic circuit.

Feedback can be improved if an auxiliary variable voltage generator va is introduced in such a way that variable voltage va is always equal to voltage developed across capacitor C.

 Applying Kirchoff's voltage law to the circuit shown,

V - iR - v_c + v_a = 0

iR = V    ,  if v_c = v_a

i = V/R

i.e. the charging current i is independent of charging capacitor C and is constant.

Voltage across capacitor , v_c = [V/CR] t

Hence, by introducing an auxiliary variable voltage generator in the basic R-C series circuit in the above manner, perfect linearity can be achieved in the output waveform of the circuit.