Detailed explanation of the switched capacitor multivibrator circuit and its waveform analysis

The switched capacitor circuit can also be used to design a switched capacitor multivibrator. The circuit is shown in Figure 6.1-5a. Op amps A1, A2 and capacitor a1C form a positive feedback loop, A1 is an integrator, and A2 is a comparator. If the comparator output voltage Vo is limited to the negative power supply Vss, the switched capacitor a2C feeds positive charge to the integrating capacitor C in each clock cycle,In this way, the output voltage V1 of the op amp A1 is correspondingly reduced by the step voltage a2lVssl (see Figure 6.1-5b). If it drops to V1<0, thenthe comparator output voltage Vo jumps to the positive power supply VDD, at this time, the coupling capacitor a1C feeds positive charge to the integrating capacitor C,Make V1 jump down to a1 (VDD-VSS). In each clock cycle thereafter, a2C feeds the negative charge-a2VDD to the integrating capacitor C, so that V1 generates a positive step a2VDD. If it rises to V1>0, Vo jumps to the negative power supply Vss. The above process continues to repeat.

If a2< a1, Vss=-VDD, the oscillation must rate of this circuit is

Where fcx is the clock frequency.

From the equation (6.1-7), we can see that the circuit in Figure 6.1-5a can be used as a frequency divider circuit.

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