Current Amplifier for Nanopore Biochips for DNA Sequencing

Discussion on the topic here.

This one came from a a major industrial research laboratory: near shot noise limited detection of 1 nA currents in 100 MHz bandwidth.
This was one that I wasn't at all sure would work: it's pretty sporty trying to detect a few dozen electrons at 100 MHz in a built-up circuit. (A 100-MHz lowpass has a time-domain response about 5 ns wide, and 1 nA in 5 ns is 31 electrons.) Obviously to get the highest available signal voltage, the input-node capacitance has to be absolutely the minimum possible: less than 1 pF.

Doing this required another novel transimpedance design, and the use of microwave transistors: 20 GHz GaAs pHEMTs and 40 GHz SiGe:C bipolars. Because performance verification of such a device is very difficult, I also designed an on-board calibrator that used the same sorts of devices to produce a 50-kHz triangular wave that was really really triangular: the corner showed less than 1 ns of curvature. When differentiated by a very small coupling capacitance, this produces a square wave current of about 10 nA at the input, which is a convenient calibration signal.