modified 6 years ago

CC amp with bootstrap

00:17:54

See IRL performance here: https://imgur.com/gallery/CvolRLf

published 6 years ago

hurz

6 years ago

yes, but it looks to me you are to much focused on the voltage gain, which is not a real gain. Place the blue trace instead on the input source and compare the input current!!! This is dramatical lower with bootstrap, and sure this drops less input swing at input resistance 10kOhm. But imported is the lesser/lower load we apply to the input AC source. We virtualy increased the input impedance!

hurz

6 years ago

http://everycircuit.com/circuit/6551957714763776

crake

6 years ago

It seems to me like the bootstrap is restricting the amount of input signal current that can flow to AC ground, and consequently reducing the voltage drop across the input resistance allowing more input voltage to fall across the equivalent resistance seen by the input signal. In terms of transconductance, this situation permits more input signal voltage to fall across Rpi, or rb', or whatever terminology one is familiar with. Is this in line with your thoughts on bootstrap seen here?

hurz

6 years ago

right, by following the input AC swing it does reduce the current trought Rb from 50uA down to ~5uA impedance goes up by factor 10! Because of the cap the DC resistance is unimportantr, but the AC is to the input source!

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