The analogue front end requires four op amps to operate. I chose ST Microelectronic's TSV634 for the first revision.
A quad pack of opamps. Taken from ST Microelectronic's TSV63x datasheet.
Some of the op amps features are:
- Rail-to-rail input and output
- Low quiescent current: typ 60µA
- Low supply voltage: 1.5V
- Gain bandwith product: typ 880kHz
- Low offset voltage:
INA321’s datasheet recommends a rather expensive set of opamps. A cheaper op amp from ST Microelectronics was deemed sufficient. As with the in amp, the key feature is the rail-to-rail input and output, operation down to 1.5 V and also its gain bandwith product. The op amp will be required to amplify the signal from the in amp by G = 62 at 256 Hz. The gain bandwith product required is:
GBW P = G ∗ f = 62∗ 256 Hz = 15.9 kHz.
Which compared to the specced 880 kHz is more than sufficient.