INTEGRATED SWITCHED-CAPACITOR FILTER FOR VIEWDATA.
Arthur H. M. van Roermund, P. M.C. Coppelmans · TU/e Research Portal · 1983
Switched-capacitor filters (or 'SC filters') have been found suitable for making fully integrated electrical filters. Since the signals in these filters are discrete in time but continuous in amplitude ('sampled-data signals'), the filters behave in some ways like analog filters and in others like digital filters. SC filters consist of switches, capacitors and amplifiers. All these components are readily integrated in MOS technology. The starting point for the design can be a doubly terminated LC filter. By setting up a signal flow graph in which the only frequency-dependent operations are integrations, a filter built up from SC integrator/adder modules can be derived directly. The method gives a filter on a single chip, with very small dimensions, low parameter sensitivity and low power consumption. No trimming is necessary in production, temperature effects are very low, the circuit can be combined with others on the same chip and analog signals can be processed without analog-to-digital conversion. The chief limitation of SC filters is the frequency range in which they can be used to advantage (up to about 100 kHz at present). A number of the above aspects are illustrated with the aid of an integrated viewdata filter, fabricated in a LOCMOS process. Its area is about 3. 3 mm**2. The power dissipation is about 10 mw at a supply voltage of 10 v.