A wide-range tunable bandpass filter cum sinusoidal oscillator using a new current-controlled resistor

The proposed design uses the exponential characteristic of BJTs to produce a new current-controlled resistor that can be electronically varied from 10 Ω to several MΩ. This resistor is used to make a bandpass filter, the resonant frequency of which is linearly tunable to a wide range of 10 Hz to 35 MHz. The filter achieves a constant Q-factor of about 30 at all frequencies (when implemented with discrete devices). The same configuration also realizes a linearly tunable sinusoidal oscillator for all frequencies. The versatility and usefulness of this low-cost design is shown by simulating a swept-tuned spectrum analyzer and a tracking (Bode plot) generator. The circuit uses only nine small-valued passive components