Adaptive low pass filter

Claim 2

An adaptive filter having a bandwidth responsive to a change of condition of an input signal comprising: an adjustable response characteristic digital filter having a control terminal; and control means coupled between the input and output of said digital filter and connected to said control terminal, said control means providing a signal to control said digital filter, said control signal being formed by the ratio of the expected noise-power of said input signal divided by a function of said input signal and the prior output signal of said digital filter.

Claim 3

The adaptive filter of claim 1 wherein said control means comprises: comparison means coupled between the input and output of said digital filter for comparing a first signal formed by said input signal with a second signal formed by the previous value of said output signal and for generating a third signal indicative of the difference between said first and second signals; root-mean-square error means connected to the output of said comparison means for generating a fourth signal formed by the average of the square of said third signal; and division means connected between the output of said root-mean-square error means and said control terminal for generating said control signal; whereby said input signal and said prior output signal are combined to form said control signal to be the ratio representing expected input signal noise divided by the average in time of the square of the difference between said input and prior output signals.

Claim 4

The adaptive filter of claim 2 further comprising: a first multiplier having two inputs and an output; an adder having two inputs and an output, last said output comprising the output of said filter; means connecting one of said multiplier inputs to the input of said digital filter; means connecting the output of said multiplier to one of said adder inputs; feedback means comprising delay means having an input and an output, and a feedback multiplier having two inputs and an output; means connecting the input of said delay means to said filter output; means connecting the output of said delay means to one of said feedback multiplier inputs; means connecting the output of said feedback multiplier to the other of said adder inputs; means connecting the other of said feedback multiplier inputs to said control signal; a subtractor having two inputs and an output; a first digital source of value unity; means connecting said digital source to one of said subtractor inputs; means connecting the other one of said subtractor inputs to said control signal; means connecting the output of said subtractor to the other of said first multiplier inputs; whereby an input signal w(k) and a prior output signal x(k-1) are combined with said control signal, denoted as a, to form said adaptive filter output so that x(k) w(k)(1-a(k)) + x(k-1) (a(k)).

Claim 5

The adaptive filter of claim 3 wherein said root-mean-square error means is comprised of: a second multiplier having two inputs and an output; means connecting both of said second multiplier inputs to the output of said comparison means; a third multiplier having two inputs and an output; a second digital number source; means connecting one of said third multiplier inputs to said output of said second multiplier; means connecting said second digital number source to the other of said third multiplier inputs; a second adder having two inputs and an output; a second delay means having an input and an output; a fourth multiplier having two inputs and an output; means connecting one of said second adder inputs to the output of said third multiplier; means connecting said output of said fourth multiplier to the other input of said second adder; means connecting said second delay means input to said second adder output; means connecting one of said fourth multiplier inputs to said second delay means output; said a third digital number source connected to the other input of said fourth multiplier.