Fet interface circuit

Claim 1

A switching circuit responsive to a first source of bilevel input signal having relatively small amplitude swing to control the coupling of a second source of signal having a relatively larger amplitude value than either of the bilevel amplitude values to a load, said circuit comprising: first means for coupling said load and said second signal source in series with the source and drain leads of a first fieldeffect transistor; second means for coupling the source and drain leads of a second field-effect transistor between the source and the gate of the first transistor; an input control circuit coupled to the gate and drain leads of the second transistor and arranged to respond to one level of the input signal to turn said second transistor ''''on'''' such that the larger valued signal is applied to both the source and gate leads of the first transistor to thereby hold said first transistor in an ''''off'''' condition, said control circuit also responding to a change from said one to the other level of said input signal to turn the first transistor ''''on;'''' said control circuit including third and fourth field-effect transistors, the source and drain leads of the third transistor being coupled between the gate lead of the second transistor and the first signal source, the gate lead of the third transistor being coupled to a bias source, the source and drain leads of the fourth transistor being coupled between the gate lead of the first transistor and a point of reference potential, and the gate lead of the fourth transistor being coupled to said first signal source; and a feedback path coupled between the drain lead of the first transistor and gate lead of the second transistor and arranged to respond to the ''''on'''' condition of tHe first transistor to charge the parasitic capacitance associated with the gate lead of the second transistor to a value which renders the second transistor nonconductive.