Other Parts Discussed in Thread: TINA-TI, ADC08100, THS5641A,
Tool/software: TINA-TI or Spice Models
Hi,
I'm making a isolated HV probe that is a ADC - ISO - DAC. I'm using ADC08100 - ISO7640 - THS5641A. Before the input to the ADC I have a 1M 20pF voltage divider, to make the input compatible with oscilloscope probes.
In the ADC08100 datasheet it suggests LMH6628 as an op amp to be used to drive the ADC. It also says : " Any input amplifier should incorporate some gain as operational amplifiers exhibit better phase margin and transient response with gains above 2 or 3 than with unity gain. If an overall gain of less than 3 is required, attenuate the input and operate the amplifier at a higher gain, as shown in Figure 32. "
If the concept works well than I would like to use the probe(s) in my lab where I work on 3-phase PFCs, DC/DC converters itd. So I would be looking at a square wave - 30Khz input in a noisy environment.
Now my questions are:
- is it batter to use the amps in unity gain and have higher input voltage (better SNR) or to use gain and attenuate the signal? Right now in the schematic I have 16X gain and for the 1.5Vppinput voltage for the ADC that gives me 94mVpp of signal after the voltage divider. This could be a problem for noise pick up.
- does this simulate with TINA-TI (the difference in phase margin and transient response?
Best regards,
Marko
