FX406

The FX406 Unifil^TM is a CMOS LSI circuit with a wide variety of signal processing applications. The device consists of a switched capacitor second-order active filter with a single input and outputs for bandpass, notch, lowpass and highpass frequency responses, together with a clock generator to provide the switched capacitor sampling clock frequency. The centre frequency of the bandpass and notch filters is the same as the cut-off frequency f_c of the lowpass and highpass filters. The filter sampling clock is derived from a multiplying phase-locked loop whose reference or input frequency is the same as the desired cut-off frequency of the filters. The PLL comprises a voltage controlled oscillator, one of two types of phase comparator, a fixed divider and an external RC loop filter. Facilities are provided to programme the cut-Off frequency of the filters by injecting an external signal into the  PLL, or by using the on-chip clock oscillator circuit. The filters have gain adjustment on the input, and the Q is programmable to eight values between 0.54 and 8.0.