How miller sweep circuit is work?

Miller sweep circuit

The miller circuit is also known as by the name of miller integrator. Above figure shows the circuit of the miller sweep circuit or miller integrator. The transistor Q₁ act as a switch and transistor Q_2­ is a high gain amplifier. If the transistor Q_1­ is ON and transistor Q₂ is OFF then the voltage across the capacitor and the output voltage is equal to V_CC. At this time suppose a pulse of negative polarity as shown in figure b is applied at the base of the transistor Q₁. Due to this emitter base junction of Q₁ gets reverse biased and then it turns OFF and transistor Q₂ is turn ON. As Q₂ conducts the output voltage gradually moves towards zero. As the capacitor C is coupled to the base of the transistor Q₂, the rate of decreases of the output voltage is controlled by the rate of discharge of a capacitor. The time constant of discharge is given by the relation,

                                                       π = R_BC

The value of time constant is very large, the discharge current will be constant due to the run down of collector voltage is linear. The transistor Q₁ turns ON while Q₂ turns OFF when input pulse is removed. If the transistor Q₁ turns OFF the capacitor C is charge quickly through resistor R­_C to V_CC having a time constant π equal to R_CC.

The resistance in the miller sweep (R_C) is replaced by a diode. The diode forward resistance Rf helps the capacitor to charge quickly from V_CC. Due to this playback time Tr of generated sweep is reduced. In this way the miller sweep circuit gives an excellent sweep linearity as compared to other sweep circuits.