What’s your (single) point, youngster?

Don't you just love an eye roll from a newbie engineer

I was asked to help a young colleague with a product that was close to production. The circuit had a detector that connected to the virtual ground of an op-amp setup to convert detector current to voltage. The detector impedance was only about 1 kΩ; the feedback resistor’s value was 100 MΩ. So, even though the op-amp circuit functioned as a transimpedance amplifier, it was also a voltage amplifier with a gain of 100,000. The unit was supposed to work with either batteries or a battery eliminator. We had tested it over the full input-voltage range, from an almost-dead battery to the highest possible eliminator voltage, but we didn’t try a battery eliminator until late in the project. When we connected the eliminator, we saw a shift of approximately 100 mV. Many theories existed regarding the cause. One engineer blamed it on breakdown phenomena involving the conductive coati...

Full article: http://www.edn.com/electronics-blogs/tales-from-the-cube/...