Circuit diagram of miller sweep generator with input and output waveform

 

Figure shows the circuit diagram of a Miller sweep generator/integrator or a sweep generator circuit, in which two transistors Q1 and Q2 are used. The function of miller sweep generator is to convert step or square waveform into ramp waveform. 

Figure: Circuit diagram of miller sweep generator or miller integrator

In the circuit, transistor Q1 acts as a switch and transistor Q2 acts a high gain common emitter amplifier. Initially consider Q1 is ON and Q2 is OFF. At this condition, the voltage across the capacitor C and the output voltage V0 is equal to voltage of +Vcc. When a negative pulse is applied to the base of Q1, it will turn OFF due to reverse biasing of emitter-base junction and hence the collector voltage of Q1 increases which increases the bias to Q2 and turned it ON. Now transistor Q2 conducts, output voltage V0 starts to decrease because of capacitor is coupled to the base of transistor Q2.

The rate of decrease of output voltage V0 is controlled by rate of discharge of capacitor and time constant of the discharge is given by

td = RB2*C.

Since value of time constant is very large, the discharge current remains constant and the rundown of the collector voltage is linear as shown in following figure. When the input pulse is removed, Q1 turns ON and Q2 turns OFF. The capacitor charges quickly to +Vcc through collector resistor Rc with the time constant

t =RC*C

Figure: Input and output waveform of Miller sweep generator

First figure shows simple circuit of miller sweep generator where practical circuit includes more stages with emitter follower and diodes (in place of collector resistor Rc). Miller sweep generator is considered the best sweep generator among the available other circuits due to its excellent sweep linearity. You can see the multisim simulation of the miller circuit in following video.