Time constant-based calibration circuit for active filters

An apparatus including time constant-based calibration circuitry for tuning active filter circuitry, comprising:

• tunable signal generator circuitry, having associated therewith a first controllable time constant, that responds to reception of a digital tuning control signal and first and second reference signals having mutually proportional respective DC value by providing a DC signal and an AC signal, wherein said DC signal has a magnitude responsive to said digital tuning control signal and related to said first controllable time constant, and said AC signal has a predetermined waveshape with a temporally variant magnitude;
• signal comparison circuitry, coupled to said tunable signal generator circuitry, that compares said DC and AC signals and in response thereto provides a digital result signal indicative of a difference between said DC and AC signal magnitudes;
• successive approximation circuitry, coupled to said signal comparison circuitry, that responds to reception of said digital result signal by providing said digital tuning control signal indicative of an approximation corresponding to a plurality of successive values of said digital result signal;
• and
• current signal generator that provides first and second DC currents as said first and second reference signals and includes
• constant current source circuitry that provides a substantially constant DC reference current, and
• current replication circuitry, coupled to said constant current source circuitry, that responds to reception of said DC reference current by providing said first and second DC currents as first and second replicas of said DC reference current.

An apparatus including time constant-based calibration circuitry for tuning active filter means, comprising:

• tunable signal generator means, having associated therewith a first controllable time constant, for responding to reception of a digital tuning control signal and first and second reference signals having mutually proportional respective DC values substantially independent of said digital tuning control signal by generating a DC signal and an AC signal, wherein said DC signal has a magnitude responsive to said digital tuning control signal and related to said first controllable time constant, and said AC signal has a predetermined waveshape with a temporally variant magnitude;
• signal comparison means for comparing said DC and AC signals and in response thereto generating a digital result signal indicative of a difference between said DC and AC signal magnitudes;
• and
• successive approximation means for responding to reception of said digital result signal by generating said digital tuning control signal indicative of an approximation corresponding to a plurality of successive values of said digital result signal.

A method of using time constant-based calibration for tuning active filter circuitry, comprising:

• receiving a digital tuning control signal;
• receiving first and second reference signals having mutually proportional respective DC values substantially independent of said digital tuning control signal;
• generating a DC signal having a magnitude responsive to said digital tuning control signal and said first reference signal and related to a first controllable time constant;
• generating an AC signal responsive to said second reference signal and having a predetermined waveshape with a temporally variant magnitude;
• comparing said DC and AC signals and in response thereto generating a digital result signal indicative of a difference between said DC and AC signal magnitudes;
• and
• processing said digital result signal for generating said digital tuning control signal indicative of an approximation corresponding to a plurality of successive values of said digital result signal.