US 8,618,872 B1Granted

Filter with controlled cut-off frequency step-down

AssigneeMarvell International Ltd.

InventorsHongying Sheng, Jun Wang

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Abstract

A filter network having a variable cut-off frequency can be controlled in a way that allows the cut-off frequency to be changed gradually to avoid undesirable transient effects. An impedance network (such as a resistor network) that provides a plurality of impedance values is provided. Logic, and a corresponding method, are provided to change the impedance value gradually, such as on a step-wise basis, to change the cut-off frequency gradually. The size of the impedance step and the duration of the step can be preprogrammed, and may be different for different types of events that trigger the need for a frequency change. It may also be possible for those preprogrammed values to be initial values only, with the values changing under programmed control during the frequency changing process. Other values, such as the initial and target impedance values that determine the initial and target frequency, also may be programmable.

Claims42

Dependent claims

A method for varying cut-off frequency of a filter when a steady state is disturbed, said method comprising:

detecting a trigger event that disturbs said steady state;
in response to said trigger event, changing a value of a circuit element of said filter to an initial value to raise said cut-off frequency from a steady-state target frequency to an initial frequency;
maintaining said initial value of said circuit element to maintain said cut-off frequency at said initial frequency for a predetermined period after said trigger event;
after said predetermined period, comparing a difference, between a current value of said circuit element and a step size, to a target value of said circuit element corresponding to said target frequency;
and:
(1) when said difference is less than said target value of said circuit element, setting said value of said circuit element to said target value of said circuit element and resuming said steady state, and otherwise:
(2)(a) changing said value of said circuit element by said step size to a new value to reduce said cut-off frequency by a frequency step to a new frequency,
(b) maintaining said new value of said circuit element to maintain said new frequency for an interval equal to a step length, and
(c) after said interval, repeating said comparing, said changing and said maintaining until, in said comparing, said difference is less than said target value of said circuit element and then performing said setting said value of said circuit element corresponding to said target value of said circuit element and resuming said steady state.

6 more elements

A filter having a variable cut-off frequency that operates in a steady state at a steady-state target frequency, said filter comprising:

means for detecting a trigger event that disturbs said steady state;
means for, in response to said trigger event, changing a value of a circuit element of said filter to an initial value to raise said cut-off frequency from said target frequency to an initial frequency;
means for maintaining said initial value of said circuit element to maintain said cut-off frequency at said initial frequency for a predetermined period after said trigger event;
and
means for, after said predetermined period, comparing a difference, between a current value of said circuit element and a step size, to a target value of said circuit element corresponding to said target frequency;
and:
(1) when said difference is less than said target value of said circuit element, setting said value of said circuit element to said target value of said circuit element and resuming said steady state, and otherwise:
(2)(a) changing said value of said circuit element by a step size to a new value to reduce said cut-off frequency by a frequency step to a new frequency,
(b) maintaining said new value of said circuit element to maintain said new frequency for an interval equal to a step length, and
(c) after said interval, repeating said comparing, said changing and said maintaining until, in said comparing, said difference is less than said target value of said circuit element and then performing said setting said value of said circuit element corresponding to said target value of said circuit element and resuming said steady state.

7 more elements

A filter having a variable cut-off frequency that operates in a steady state at a steady-state target frequency, said filter comprising:

circuitry to detect a trigger event that disturbs said steady state;
extension logic comprising logic to, in response to said trigger event, change a value of a circuit element of said filter to an initial value to raise said cut-off frequency from said target frequency to said initial frequency, and to maintain said initial value of said circuit element to maintain said cut-off frequency at said initial frequency for a predetermined period after said trigger event;
and
stepping logic that, after said predetermined period, compares a difference, between a current value of said circuit element and a step size, to a target value of said circuit element corresponding to said target frequency;
and:
(1) when said difference is less than said target value of said circuit element, sets said value of said circuit element to said target value of said circuit element and resuming said steady state, and otherwise:
(2)(a) changes said value of said circuit element by a step size to a new value to reduce said cut-off frequency by a frequency step to a new frequency,
(b) maintains said new value of said circuit element to maintain said new frequency for an interval equal to a step length, and
(c) after said interval, repeats said comparing, said changing and said maintaining until, in said comparing, said difference is less than said target value of said circuit element and then sets said value of said circuit element corresponding to said target value of said circuit element and resumes said steady state.

6 more elements

Dependencies are inferred from the claim text.