Fast high input impedance unity gain buffer

Q1 and Q2 form a simple high-speed FET input buffer. The role of Q1 is to act as a source follower, and the current source load of Q2 controls the drain-source channel current. Usually, this open loop setting is very unfixed because there is no DC feedback. The function of the LTC1052 is to make the circuit more stable by comparing the filter circuit output to a similar filtered input signal.