Patent ID: 6356143
Filing Date: 2002-03-12
Classification: H03B,H03J

Abstract:
A variable bandpass filter system, comprising:a first switch to receive an RF input signal and an oscillating calibration signal, said first switch operating to pass said RF input signal or said oscillating calibration signal based a control signal; and a first active filter circuit having a first oscillator, said first active filter circuit to receive output of said first switch, and frequency and gain control signals, said frequency control signal selecting an operating frequency of the first oscillator, such that said operating frequency determines a range of frequencies to pass within said RF input signal, and said gain control signal selecting gain of the first oscillator, where said first oscillator includes a negative resistance circuit, including: a transistor having base, collector, and emitter terminals, the collector terminal connected to a first voltage source, and the emitter terminal connected to a second voltage source through a first resistor, a second resistor coupled between the first voltage source and the base terminal of the transistor, a third resistor coupled between the base terminal of the transistor and the second voltage source, and a pair of series capacitors connected in parallel to said first resistor, where said first switch enables said first oscillator to be calibrated by passing the oscillating calibration signal.