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How to improve transimpedance amplifiers with a bootstrap?
Improving transimpedance amplifiers with a bootstrap. For example, with 5pF of photodiode capacitance, bootstrapping the JFET has very little effect because the input capacitance is dominated by the photodiode not the JFET. However, bootstrapping the photodiode will increase the bandwidth from 24MHz to 81MHz.
Why do you need an analog bootstrap circuit?
Analog bootstrap circuits are traditionally ones where an output is fed back to the input, usually to increase input impedance. This can be to minimize either the resistive or reactive (usually capacitive) components of the input impedance or both.
How is a bootstrap capacitor used in a transistor?
It typically involves the use of a bootstrap capacitor, which provides positive feedback of ac signals to the base junction of a transistor in an emitter follower circuit. Application of this feedback increases the effective value of the base resistance.
Can a bootstrap increase the JFET to 130mhz?
Then bootstrapping the JFET will further increase that to 130MHz because the effective photodiode capacitance has been reduced and the JFET gate-drain capacitance is significant again. Bootstrapping the JFET on its own will only increase the bandwidth from 24MHz to 27MHz.
Is the gain stage of a transimpedance amplifier infinite?
Similarly, the gain stage will not have infinite bandwidth. Overall though, the technique is very useful in trying to design high transimpedance, high bandwidth transimpedance amplifiers for photodiodes, including avalanche photodiodes.
How are transimpedance amplifiers used in avalanche photodiodes?
Overall though, the technique is very useful in trying to design high transimpedance, high bandwidth transimpedance amplifiers for photodiodes, including avalanche photodiodes. The techniques can be used with custom IC-based implementations as well as discrete circuits, and for circuits with discrete devices mixed with opamps.