A single-transistor tunable filter for Bluetooth applications

In this paper a wide dynamic range, high-Q, tunable filter realized with a single-transistor active inductor (AI) is presented. A single-transistor amplifier combined with a compensation network allows the control both of the equivalent inductance and of its series resistance in a wide frequency range. The proposed AI has been used in the design of a first-order band-pass filter with a central frequency of 2400MHz with a -3dB bandwidth less than 15MHz in a frequency range of 100MHz around the central frequency. Both attenuation and resonant frequency can be controlled. A dynamic range of 75dB is obtained with a noise figure of 10dB.