Delay circuit employing active bandpass filter

Claim 1

In a delay circuit of the type comprising an input node for receiving an input signal to be delayed, active bandpass filter means having an input coupled to said node and an output for providing a bandpass filtered output signal voltage, voltage-to-current converter means having an input coupled to said node and an output for providing an output signal current proportional to the amplitude of said input signal and independent of the frequency thereof, and active signal combining means responsive to said signal voltage and to said signal current for providing a delayed output signal, the improvement for minimizing quiescent power dissipation of said delay circuit, characterized in that: said filter means includes first transistor means biased to regulate a DC component of said output signal voltage at a predetermined value equal to the sum of a DC reference voltage supplied to said first transistor means and a threshold voltage characteristic of said first transistor means; said combiner means includes second transistor means having a threshold voltage substantially equal to that of said first transistor means, having a control electrode coupled to receive said signal voltage, having a conduction path coupled at a first end thereof to a source of supply voltage via a load resistor for developing said delayed signal and coupled at a second end thereof to receive said signal current, said signal current including a DC component providing the sole source of quiescent operating current for said second transistor means; and a resistor in said combiner means coupled between said second end of said conduction path of said second transistor means and a source of said DC reference voltage for maintaining a substantially zero quiescent power dissipation in said resistor means, said resistor means controlling the ratio of components of said delayed signal attributable to said signal current and to said signal voltage.