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Stray capacitance between the input and output in amplifier circuits can be troublesome because it can form a path for feedback, which can cause instability and parasitic oscillation in the amplifier. It is often convenient for analytical purposes to replace this capacitance with a combination of one input-to-ground capacitance and one output ...
In electronics, the Miller effect (named after its discoverer John Milton Miller) accounts for the increase in the equivalent input capacitance of an inverting voltage amplifier due to amplification of the effect of capacitance between the amplifier's input and output terminals, and is given by
The input charge and the output voltage are proportional with inverted sign. The feedback capacitor C f sets the amplification. = = The input impedance of the circuit is almost zero because of the Miller effect. Hence all the stray capacitances (the cable capacitance, the amplifier input capacitance, etc.) are virtually grounded and they have ...
Bootstrapping is a technique in the field of electronics where part of the output of a system is used at startup.. A bootstrap circuit is one where part of the output of an amplifier stage is applied to the input, so as to alter the input impedance of the amplifier.
The sensors which transimpedance amplifiers are used with usually have more capacitance than an op-amp can handle. The sensor can be modeled as a current source and a capacitor C i. [4] This capacitance across the input terminals of the op-amp, which includes the internal capacitance of the op-amp, introduces a low-pass filter in the feedback path.
Using Miller's theorem, the circuit of Figure 4 is transformed to that of Figure 5, which shows the Miller capacitance C M on the input side of the circuit. The size of C M is decided by equating the current in the input circuit of Figure 5 through the Miller capacitance, say i M, which is:
The Miller Effect means that when this capacitance is in the feedback path, it results in an effective input capacitance that is multiplied by the stage gain: a feedback capacitance of only 1.0 pF in a circuit with a voltage gain of 50 results in an effective input capacitance of 51 pF.
It may be observed as an undesired Miller effect in common-emitter, common-source and common-cathode amplifying stages where effective input capacitance is increased. Frequency compensation for general purpose operational amplifiers and transistor Miller integrator are examples of useful usage of the Miller effect.