Patent ID: 7212068

Claim:
A filter circuit assembly comprising: at least one filter stage, said filter stage comprising at least one variable resistor, a resistor/capacitor (RC) oscillator having an output, said RC oscillator further comprising at least one variable resistor; a successive approximation register coupled to the output of the RC oscillator and generating a control value corresponding to the output of the RC oscillator, where the control value of the successive approximation register controls the resistance of the variable resistor of the filter stage and the resistance of the variable resistor of the RC oscillator, and where the successive approximation register compares a frequency of the RC oscillator to a reference frequency to generate the control value; wherein the variable resistor of the filter stage and the variable resistor of the RC oscillator have a substantially identical structure, where each variable resistor structure is closely coupled to a power supply terminal of the filter circuit assembly, and the variable resistor structure comprises a plurality of resistors coupled in series with one another and a plurality of transistors, each transistor coupled in parallel with a corresponding one of the plurality of resistors, where a gate of each transistor is coupled to a corresponding bit of the successive approximation register.