A for Amplifier
Which OpAmp should I use for lowest 1/f (flicker) noise?
Trick question, you need a composite amplifier with the IF3601 from InterFET. The question should be: Which part should I choose that doesn't break the bank?
After an exhaustive search I came up with the following:
| PN | e_n @ 1kHz | e_n 0.1 Hz - 10 Hz | Ib @ 25°C | USD @ 1ku |
|---|---|---|---|---|
| OPA210 | 2.2 nV/√Hz | 90 nVpp | ±0.3 nA | 1.328 |
| OPA211 | 1.1 nV/√Hz | 80 nVpp | ±60 nA | 5.732 |
| AD797 | 0.9 nV/√Hz | 50 nVpp | 250 nA | 7.93 |
| LT1028 | 0.9 nV/√Hz | 35 nVpp | ±50 nA | 6.43 |
Above are for SOIC packages only, LT1028 can be had in a more expensive PDIP package but with 0.85 nV/√Hz input referred noise.
Depending on available board space and other constraints, this should help making a decision for which trade-off to take. The OPA210 is the newest part of the bunch and it shows in its characteristics and price point. Although it has the highest noise level of the bunch, paralleling a lot of them will still to an input bias current at least 10x lower than the next best of the older parts. Depending on the application this might be useful, or not. In a future post I'll explore what's possible by paralleling a bunch of them for a research project and maybe even build a chopped, discrete JFET input stage, composite amplifier to show what's possible by combining latest advancements with the most refined process technology that JFETs can yield. Though instead of IF3601 I might go with a JFE2140 pair.