uses Ql and Q2 constitute a simple, high-speed FET input buffer.Â·Ql functions as a source follower, with the Q2 current-source load setting the drain-source channel current. The LT1010 buffer provides output drive capability for cables or whatever load is required.
The LTC1052 stabilizes the circuit by comparing the filtered circuit output to a similarly filtered version of the input signal. The amplified difference between these signals is used to set Q2`s bias, and hence Ql`s channel current. This forces Ql`s V0 s to whatever voltage is required to match the circuit`s input and output potentials. The diode in Ql`s source line ensures that the gate never forward biases and the 2000-pF capacitor at Al provides stable loop compensation.
The rc network in Al `s output prevents it from seeing high-speed edges coupled through Q2`s collector-base ]unction. A2`s output is also fed back to the shield around Ql `s gate lead, bootstrapping the circuit`s effective input capacitance to less than 1 pF.