A 20 MHz 6th order BiCMOS programmable filter using parasitic-insensitive integrators

A fast parasitic-insensitive continuous-time filter that uses an active integrating-capacitor is described. The filter IC consists of a sixth-order Bessel lowpass and a second-order cosine-equalizer stage. It is made up of three biquads with lowpass and bandpass outputs. Both outputs of the last stage are available with matched group-delay characteristics. The corner frequency is digitally programmable through the digital serial interface to 64 values over a 4 to 1 range. Techniques for excess-phase nulling and Gm-setting independent of supply and temperature are described. This 20 MHz, 5 V equalizer has 0.24% of total harmonic distortion with 2 Vp-p signals and is built in 1.5 mu m/4 GHz BiCMOS.<
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