Nuclear Nonproliferation: 100-MHz Noise Cancelling Front End

This was in cooperation with Mesa Photonics of Santa Fe NM. It's part of a DOE program, an advanced deployable solar occultation spectrometer for detecting volatile plumes from clandestine uranium enrichment.

Their scheme uses a really cool technique: solar heterodyne detection.  It's a good illustration of the importance of a photon budget.

32-Channel IR Detector for Compressive Scanning Camera

A follow-on to the single channel version. This one had to work at very much lower power, which required a new amplifier topology based on local feedback around a very low noise JFET. This was a very fruitful development, which has been used in a number of follow-on designs.

Compressive-Scan Camera: 1-Channel IR Detector Analog Front End

In cooperation with InView Technology. Compressive scanning is a scheme for doing image sensing with a single-element detector, without suffering the N2 speed penalty of raster scanning. It's a sort of combination of scanning and image compression—you use a digital micromirror device (DMD) to multiply the image by a series of 1-bit digital basis functions, measure the resulting photocurrent, and then invert the transform to produce a compressed image. That's not too useful in the visible, where image sensors are cheap commodity items, but in the UV and especially the shortwave IR (SWIR), image arrays are extremely expensive, so there's a need for compressive scan cameras.


This front end had to reach the shot noise limit with high-capacitance SWIR photodiodes at very low photocurrents, which is a difficult combination.

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.

Instrumentation: Wideband Laser Noise Canceller

> 60 dB of laser RIN cancellation out to > 10 MHz, about 100 times faster than current commercial devices