Anyone have any experience with rectification effects in ZD op-amps?
Seeing some odd effects with a rather simple amplifier using an LT2057 high voltage ZD op-amp.
I'm very suspicious that some newer models offer EMI hardness as a feature...
--sp
-- Best regards, Spehro Pefhany Amazon link for AoE 3rd Edition: http://tinyurl.com/ntrpwu8 Microchip link for 2015 Masters in Phoenix: http://tinyurl.com/l7g2k48
No, but I have seen DC offsets that were a function of the capacitance seen by the two inputs. Some sort of charge injection thing, several microvolts of offset.
-- John Larkin Highland Technology, Inc lunatic fringe electronics
I don't know, as I put on RF filtering as a matter of course when desiging a board for measuring microvolt signals, and the zero-drift opamps that I prefer are only available in MSOP so I normally make a board if I use them. Even when I make the board with a scalpel on blank FR4, I still include the RF filtering parts.
I have seen RF rectification plenty of times on veroboard amplifiers with non-zero-drift ordinary bipolar op-amps. It is something that you are likely to care about when measuring microvolt signals which is the same situation where you might buy a zero-drift op-amp, so EMI-hardness may be offered on newer op-amps just because it is useful in their typical applications, not necessarily because they are worse than other op-amps.
I have found it useful to get a RF signal generator, plug in a piece of coaxial cable and strip the end, and connect e.g. a 5.6pF capacitor in series with the inner conductor, and go around the amplifier circuit blasting each external IO terminal with e.g. 0dBm or +10dBm at 1GHz (or try a few frequencies if you have time), and measure how much the DC output voltage changes with RF on and off. On one RTD amplifier I was able to reduce the sensitivity to RF quite a lot by adding an adhesive copper tape ground plane and a bunch of surface mount filtering capacitors, even though the amplifier was still built on stripboard.
Chris
ElectronDepot website is not affiliated with any of the manufacturers or service providers discussed here. All logos and trade names are the property of their respective owners.