I once chose a TO-99 packaged, low-noise op-amp, the OPA2111 when that device was a product of Burr-Brown. Today, that device is being sold by Texas Instruments.
I got some really nice results with it, but I was just plain lucky to have avoided trouble with that part from a noise source I hadn't reckoned with, ambient light.
The OPA2111 uses a pair of junction FETs for its differential input stage. The trademark for this feature is now Difet ®.
According to a Burr-Brown tech-rep with whom I spoke way back then, those two FETs were quite large, occupying approximately 50% of the chip's area all by themselves. Being large, those FETs were highly sensitive to ambient light that could sneak into the package via the glass beads that held the eight leads of the TO-99 can.
Continue reading "A Sneak Noise Source - John Dunn, Consultant, Ambertec, P.E., P.C." »