Accurate square-law detector circuit

Claim 1

A square-law detector comprising an operational amplifier in the form of a high-gain difference amplifier, a diode having an approximate square-law region of operation having one side thereof connected directly to one input of said difference amplifier and the other side adapted to be connected to a modulateD ac input signal, the other input of said difference amplifier connected to a signal ground, a feedback resistance connected across said amplifier to carry a signal current equal to the forward diode current produced by the input signal, a first bias resistance connecting the cathode of said diode to a source of constant negative voltage relative to the anode thereof, and a second bias resistance connecting the anode of said diode to a source of constant positive voltage relative to said cathode, the resistances of said bias resistances being chosen to provide a forward d.c. bias current through said diode at which the most optimum square-law relation occurs and also to provide a desired dc operating point at the output of said amplifier, whereby said one input of said difference amplifier is maintained substantially at signal ground potential during operation and the output voltage of said amplifier is essentially proportional to the square of the forward signal voltage across said diode.