Has anyone made an isolated linear signal circuit using photodiode matched pairs? As in AoE III, Figure 12.88.D, page 848, and Fig 12.90, page 849? We list in Fig 12.88 the HCNR201, IL300 and LOC110. They claim 0.01% linearity, much better than I need. I'm thinking if I run one of those blokes at a high photodiode current, it should be possible to make a very fast isolated signal transmitter.
This is for my RIS-764 project, which is a 1.2kV 10ns 20A pulse generator using a pair of new SiC MOSFETs (similar to AoE Figure 12.44.H, page 822).
This is to monitor the current though the flying output node. Note, that node includes a nifty +20V,-4V flying power supply, which can run the photodiode isolator's op-amp and LED.
I'll have to deal with the current generated by the flying node's more than 50kV/us slew rate into the isolator's coupling capacitance. That's 0.4pF for the HCNR201, which will create about 20mA for 5 to 10ns, swamping the photodetector's meager 0.5% output. I can add cancelling and a blanking circuit to the receiving end. I'll be happy with us, rather than ns, response speed.