Reducing EF input impedance. 1. Bootstrapping input network to suppress current drain through Rcm biasing resistor
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<span class="int-own-work" lang="en">Own work</span> // The basic idea was known for over half a century, cf. T. D. Towers. High Input-Impedance Amplifier Circuits - Wireless World - 1968 July pp. 197-201. or a modern review in David Self's Small Signal Audio Design (any edition, chapter 3