Integrated electric filter with adjustable RC parameters
AssigneeU.S. Philips Corporation
InventorJohn B. Hughes
Life of this patent
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Abstract
An integrated electrical filter includes resistors (R10-12) and capacitors (C10-12). The capacitors are controllable in value by means of a control circuit (100-109) and are formed by a binary weighted array of capacitor elements which are selectively connectable in parallel. A controlled oscillator (103) or a controlled phase shifting network (113) includes a capacitor of the same form as the filter capacitors. The oscillator (103) or phase shifter (113) form part of a phase locked loop (101, 104, 105, 107) which produces a digital code as its control signal at the output of an up/down counter (107). This digital code is latched in a register (109) to provide a control signal for the filter capacitors and also is used directly to control the capacitor(s) in the controlled oscillator or phase shifter.
Claims21
An integrated electrical filter comprising at least one filter resistor, at least one filter capacitor and a control circuit for adjusting the value of the product of the resistance of the filter resistor and the capacitance of the filter capacitor, the control circuit comprising a phase detector, means for feeding a first signal to a first input of the phase detector, means for feeding a second signal to a second input of the phase detector, means for modifying the second signal in response to an output of the phase detector to cause the first and second signals to tend towards a given phase relationship, said modifying means including a control capacitor and a control resistor, characterised in that the control capacitor or control resistor comprise a plurality of capacitor or resistor elements, respectively that the output of the phase detector is effective to interconnect selected ones of the capacitor or resistor elements to give the control capacitor or control resistor a selected value, and that the control circuit further comprises means for adjusting the value of the filter resistor or filter capacitor, respectively in dependence on the selected value of the control resistor or control capacitor.
A filter as claimed 1 wherein the first signal comprises an externally generated signal and the second signal is generated by a controllable oscillator having a frequency determining network which comprises the control resistor and control capacitor.
An integrated electric filter comprising at least one filter resistor device, at least one filter capacitor device and a control circuit for adjusting the value of the product of the resistance of the filter resistor device and the capacitance of the filter capacitor device, the control circuit comprising a phase detector, means for feeding a first signal to a first input of the phase detector, means for feeding a second signal to a second input of the phase detector, means for modifying the second signal in response to an output of the phase detector to cause the first and second signals to tend towards a given phase relationship, said modifying means including a control capacitor arrangement and a control resistor arrangement, at least one of said arrangements comprising a plurality of elements selectively interconnected in response to an output signal of the phase detector to give said one arrangement a desired value, and wherein the control circuit further comprises means for adjusting the value of the product of the resistance of the filter resistor device and the capacitance of the filter capacitor device in dependence on the value of said one arrangement.
Dependencies are inferred from the claim text.