Rate controlled noise filter

• US 5,233,245 A
• Filed: 09/23/1991
• Issued: 08/03/1993
• Est. Priority Date: 04/10/1991
• Status: Expired due to Term

• Current Assignee: General Electric Company
• Original Assignee: General Electric Company
• Inventors: Romano, Timothy J., Shinkle, William R.
• Primary Examiner(s): Callahan, Timothy P.
• Application Number:
  US07/763,783
• Time in Patent Office: 680 Days
• Field of Search: 307/520, 307/521, 328/167, 364/724.01, 364/825
• US Class Current: 327/553
• CPC Class Codes: H03H 11/04 Frequency selective two-port networks

Abstract

A rate controlled noise filter according to the present invention comprises a transient detector adapted to receive an input signal and detect the rate at which the input signal is changing. The transient detector may be, for example, a filter having a second order filtered rate. The output of the transient detector is input to a function generator which outputs a signal indicative of the rate of change of the input signal. A noise filter, including a controllable time constant, also filters the input signal. The output of the function generator controls the time constant of the noise filter.

Claims

1. A rate controlled noise filter comprising:

a first filter which receives an input signal;

a second filter which receives said input signal;

a summing junction which receives said input signal at a first input, and an output signal from said first filter at a second input;

a third filter which receives an output signal from said summing junction; and

a function generator which receives an output from said third filter and which generates a signal which controls a time constant of said second filter.

2. A rate controlled noise filter according to claim 1 wherein:

said first, second and third filters are first order lag filters; and

said function generator is a lookup table.

3. A rate controlled noise filter according to claim 2 wherein:

said second filter has a transfer function of;

space="preserve" listing-type="equation">O(s)=[A/(Ts+1)]*I(s)

where,

O(s) is the laplace transform of output signal of said filter;

A is a gain constant;

T is an adjustable time constant of said filter;

s is the laplace transform operator; and

I(s) is the laplace transform of input signal to said filter.

4. A rate controlled noise filter according to claim 3 wherein:

said first and third filters have a transfer function of;

space="preserve" listing-type="equation">O(s)=[A/(β

s+1)]*I(s)

where,

O(s) is the laplace transform of output signals of said filters;

A is a gain constant;

β

is the time constant of said filters;

s is the laplace transform operator; and

I(s) is the laplace transform of input signals to said filters.

5. A rate controlled noise filter comprising:

a transient detector which receives an input signal;

a function generator which receives an output of said transient detector; and

a controllable filter which receives said input signal wherein a time constant of said controllable filter is controlled by an output signal from said function generator;

said transient detector comprising;

a first filter which receives said input signal;

a summing junction which receives an output signal from said first filter at a first input and said input signal at a second input; and

a second filter which receives an output signal from said summing junction.

6. A rate controlled noise filter comprising:

a transient detector which receives an input signal;

a function generator which receives an output of said transient detector; and

a controllable filter which receives said input signal wherein a time constant of said controllable filter is controlled by an output signal from said function generator;

said transient detector comprising;

a summing junction which receives an output signal from said controllable filter at a first input and said input signal at a second input; and

a first filter which receives an output signal from said summing junction.

7. A rate controlled noise filter comprising:

a first summing junction which receives an input signal and a modified output signal;

a first filter circuit which receives an output of said first summing junction;

a function generator which receives an output of said first filter circuit;

a first multiplier circuit which receives said input signal and an output signal from said function generator;

a second filter circuit which receives an output of said first multiplier circuit wherein, said modified output signal is generated by said second filter circuit.

8. A rate controlled noise filter according to claim 7 wherein:

said first filter circuit comprises;

a first filter summer circuit which receives an output from said first summing junction and adds said input to a first feedback signal;

a first min/max circuit which receives an output of said summer and generates a first filter output signal;

a first delay circuit which receives said first filter output signal and generates said first feedback signal.

9. A rate controlled noise filter according to clam 8, wherein;

said second filter comprises;

a second filter summer circuit which receives an output from said first multiplier circuit and adds said output from said first multiplier circuit to a second feedback signal;

a second min/max circuit which receives an output of said summer and generates a second filter output signal;

a second delay circuit which receives said second filter output signal and generates said modified output signal;

a multiplier circuit which receives said modified output signal and an output from said function generator and generates said feedback signal.