R. f. coupled line receiver with d. c. isolation

Claim 2

A circuit arrangement for eliminating noise from a given signal comprising: means for receiving a digital signal and converting said digital signal to an RF signal, said means having a first and second input and a first and second output terminal, the first input terminal of said receiving means representing a first DC ground reference; means for reconverting said RF signal to said digital signal, said reconverting means having a first and second input and a first and second output terminal, the first output terminal of said reconverting means representing a second DC ground reference; and means to couple said receiving means to said reconverting means, whereby the signal to noise ratio of said receiving circuit is improved by having the ground reference for said received digital signal DC electrically isolated from the ground reference for said reconverted digital signal.

Claim 3

A circuit arrangement according to claim 1 wherein said receiving means is an oscillator circuit, and said digital signal activates said oscillator by operating as the source of power for said oscillator.

Claim 4

A circuit arrangement according to claim 1 wherein said coupling means include a first and second capacitor, said first capacitor being connected between said first output terminal of said receiving means and said first input terminal of said reconverting means, said second capacitor being connected between said second output terminal of said receiving means, and said second input terminal of said reconverting means, said capacitors providing DC ground isolation between said receiving means and said reconverting means, said isolation being determined by the breakdown voltage of said capacitors.

Claim 5

A circuit arrangement according to claim 3 wherein the capacitance of said capacitors is less than 10 pf.

Claim 6

A circuit arrangement according to claim 1 wherein said reconverting means is a detector circuit comprising an input diode having an anode and a cathode, and a transistor having an emitter base and collector, said cathode of said diode being connected to said base, said collector being connected to a supply voltage through a first resistor, means to connect said emitter to said anode of said diode, said emitter being connected to said second ground reference, the output of said detector circuit being obtained across the collector and emitter of said transistor so that when said RF signal is applied across said diode said transistor is always on and in the absence of said RF signal said transistor turns off.

Claim 7

A circuit arrangement according to claim 5 wherein said connecting means comprises a resistor.

Claim 8

A circuit arrangement according to claim 2 wherein said oscillator circuit includes a first, second, third, fourth and fifth transistor each having an emitter, base and collector, each collector being connected to said digital signal through a resistor, each emitter being connected to said first ground reference, said first collector being connected to said second base, said second collector being connected to said third and fifth base and said third collector being connected to said first and fourth base, said oscillator output being taken between said fourth and fifth collector.

Claim 9

A circuit according to claim 1, further comprising, amplifier means coupled to said reconverting means, said amplifier means having the same ground reference as said reconverting means.

Claim 10

A circuit according to claim 8 wherein said amplifying means includes a first, second, third, and fourth transistor each having an emitter, base and collector, said first and second emitters each being connected to said second ground reference through a resistor, said second and third collector each being connected to a supply voltage through a resistor, said first collector being connected to said supply voltage, said fourth emitter being connected to said second ground reference, said first emitter being connected to said second base, said second emitter being connected to said fourth base, said second collector being connected to said third base, said third emitter being connected to said fourth collector and said output being taken between said fourth collector and said second ground reference whereby the amplifier output is in phase with said digital signal received by said oscillator circuit.