Morning everyone,
It is for another high-bandwidth current measurement attempt, in parallel to the Rogowski coil research. The bandwidth is assumed to be
2MHz; the shunt voltage is differential amplifier -> ADC driver -> high-resolution SAR ADC.Ideally, the amplification should be ~40 times to cover the full ADC range. So:
- There are four-terminal shunts widely available, so there should be no issue. The connections may cause problems, e.g. due to the contact voltage. Welding instead of soldering and some digital offset cancellation might be necessary.
- Then there will be two cascaded amplification stages based on the OPA189 with a gain of 6.3 each. The specs are insane for that price:
- The common-mode voltage will be well within the opamp's capabilities (it is rated up to 36V VCC), but not spoiling the accuracy would require insanely precise resistors. 0.1% would give me only ~60dB of CMRR. So floating the entire pipeline looks better, despite the added complexity. What do you think?
- What to do with that 1.25V signal to drive a differential ADC? Just buffer the +end with another OPA189 and apply the common-mode voltage to the -end or should I use a more fancy single-ended to differential converter? If so, what would be the secret sauce?
What else can go wrong?
Best regards, Piotr