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Method and apparatus for tuning a continuous time filter

  • US 5,914,633 A
  • Filed: 08/08/1997
  • Issued: 06/22/1999
  • Est. Priority Date: 08/08/1997
  • Status: Expired due to Term
First Claim
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1. A circuit combining an active RC filter and an integrating tuner wherein in a first state said circuit functions as a filter and in a second state said circuit functions as an integrating tuner and provides an output suitable for adjusting a total capacitance of an array of switched capacitors, said circuit comprising:

  • an amplifier having an inverting and a non-inverting input and an output;

    a resistor connected between said inverting input and a first switch;

    said non-inverting input connected to a first reference voltage; and

    a capacitor connected between the output of the amplifier and the non-inverting input;

    a pulse generator receiving the output of the amplifier as input and providing a pulse signal as output, said pulse signal having a first output signal level when the pulse generator input has a magnitude between that of a second and a third reference voltage and otherwise having a second output signal level;

    a counter receiving said pulse signal as input and providing a digital count as output, said digital count having a valve proportional to the width of a pulse present in said pulse signal; and

    a decoder receiving said digital count as input and providing a digital code as output;

    wherein, when said circuit is in the first state, said first switch connects said resistor to a filter input, said amplifier, resistor, and capacitor comprise said active RC filter, the output of the amplifier providing a filtered version of a signal applied to said filter input; and

    when said circuit is in the second state, said first switch connects said resistor to a fourth reference voltage, said amplifier, resistor, and capacitor comprise an integrator having an RC time constant defined by said resistor and capacitor, said integrator, pulse generator, counter, and decoder comprise said integrating tuner, said digital count indicating the magnitude of the RC time constant, and said digital code indicating which of said plurality of capacitors in said array of switched capacitors is to be enabled so as to tune the total capacitance of said capacitor array in accordance with said RC time constant.

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