Patent ID: 8693591

Claim:
A circuit for tuning a bandpass filter to an offset frequency of an RF frequency, comprising: a bandpass filter including a negative resistance oscillator configured to generate an oscillator in-phase clock and an oscillator quadrature clock in response to an oscillator control signal, the oscillator in-phase clock and the oscillator quadrature clock each having an oscillator base frequency; an offset frequency converter configured to generate a bi-level in-phase offset clock and a bi-level quadrature offset clock based on the oscillator in-phase clock, the oscillator quadrature clock, and a first reference clock having a reference base frequency, the bi-level in-phase offset clock and the bi-level quadrature offset clock each having an oscillator offset frequency; a sample/hold configured to sample and hold the bi-level quadrature offset clock using the bi-level in-phase as a sampling clock to generate a side location signal; a frequency detector configured to compare the oscillator offset frequency with a reference offset frequency based on the bi-level in-phase offset clock, the bi-level quadrature offset clock, and a reference offset clock having the reference offset frequency, to generate a direction signal; an inverter configured to invert the direction signal; a NOR gate configured to perform a logical NOR operation on the side location signal and the direction signal to generate a NOR signal; a NAND gate configured to perform a logical NAND operation on the inverted direction signal and the side location signal to generate a NAND signal; a multiplexer configured to output either the NOR signal or the NAND signal as a multiplexer output signal based on a selection signal; a digital controller and memory circuit configured to generate the oscillator control signal based on the multiplexer output signal.