Digitally-tunable continuous-time filters with high signal linearity

The design and evaluation of digitally tunable continuous-time filters exhibiting very high signal performance is presented. One method of achieving frequency response adjustability is to replace all time-constant determining capacitors in an active RC structure with variable capacitive components. If each variable capacitive component is a digitally-programmable capacitor array then passive capacitors (i.e. not p-n junction capacitors) can be used. Through careful design it can be ensured that the signal swing across nonlinear parastic elements (e.g. MOS switch capacitance and resistance) is minimal. Hence the signal performance of the filter is determined by highly linear passive resistive and capacitive elements. Such a method is particularly suitable for low frequency applications which do not require precision response accuracy