OK I resent attachment
View attachment IA147.png
Suppose
On + input Instrumetation amplifier is voltade from +-12,5uV to +- 1,25uV sinus max frequency 100kHz
On - input Instrumetation amplifier is voltade near 0 but not nul may be feww uV max +- 1,23mV
ISS this voltage amplifi 1x or max 20x
Secon stage - 4th LPF on 100kHz reduce energy on noise between 100kHz and 5MHz
Third stage is inverting amplifier and level shiffter, who make from +-1,25V 0-2,5V and drivimg ADC , may be 14bit 10MSPS.
We also measure phase shift, so the amplifier must significantly and randomly change the phase!
What's discussion?
Found in the first case will allow the entire process chain DC voltage.
(C5 is clamped)
Important feature of the amplifier becomes input offset voltage and his temperature shift.
According to my, this discriminates amplifier as opa134, because +-3mV input voltage offset make on 4pcs amplifier error - 12mV
without requiring DC. Is possible add before last amplifer blocking capacitor and input voltage shift will be of interest only at the last amlifier.
I simulate thiw circuits with AD8620 and the overall accuracy was acceptable (Pricing has not) :grin: