[Groth]

I used it in version .2 of the CPU-ammeter. It works well, as long as you use high-speed opto's. The initial (v.19?) test with bog standard transistor-out opto's suffered from tons of glitches, likely from the master clock returning high before the slave data could be pushed across the isolation.

The old analog isolation actually performed extremely well; I couldn't detect any difference between the sides. But the isolation-amps I had were really expensive. Especially considering that they were single channel, whereas the digital isolation allows as many devices as I want, up to the bus limits.

In V.2 I replaced the 20 mOhm shunt with a 5 mOhm version, and made some minor changes in filtering and offset control. Between 30 and 40 mV shunt drop, it performed well. Below that, the scatter plot showed increasing divergence, hitting +/-3% at 15 mV. Worse yet, there was a marked rise (1.5%) in the transfer function going from 2.0 to 2.5 Vcore. Could've been uncompensated offset or insufficient common mode rejection.

I've pushed the cheap amps as far as I can; the UPS man should be here tomorrow with better bits.

In some amp pdf I was reading (which one? :shrug: ), they talked about noise propagation in cascaded amplifiers. It convinced me to try some gain in the difference stage for version .3. I'm also planning to roll back the first stage filter to it's former 1 Mhz corner - I don't want to throw out what may be signal when summed with the other channels.

Don't s'pose you could borrow that oscilloscope again, and take a peek at the switching noise?