Tone detection and switching circuit

Claim 1

A tone detector comprising: an input for a tone having a given frequency; a tuned circuit coupled to said input, said tuned circuit being tuned to said given frequency; a precision halfwave rectifier circuit coupled to said tuned circuit; and an output circuit coupled to the output of said rectifier circuit and to said tuned circuit to produce a full wave rectified output signal with voltage gain upon detection of said tone; said tuned circuit including ground potential, a first resistor having one terminal connected to said input, and a parallel coupled inductor-capacitor tuned circuit coupled between the other terminal of said first resistor and said ground potential; and said rectifier including a first solid state operational amplifier having an inverting input, a non-inverting input and an output, said non-inverting input being directly connected to said ground potential, a second resistor coupled between the junction of said first resistor and said parallel tuned circuit and said inverting input of saiD first amplifier, a first solid state diode being poled in a given direction connected between said output and said inverting input of said first amplifier, and a series circuit coupled between said output and said inverting input of said first amplifier in parallel with said first diode, said series circuit having a second solid state diode poled in a direction opposite to said given direction, and a third resistor.