US 5,691,929 AGranted

90-degree phase shift network, system for controlling a 90-degree phase shift characteristic of the network, linearizer using all-pass filters, and system for controlling the linearizer

AssigneeIcom Incorporated

InventorWeimin Sun

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Abstract

A 90-degree digital phase shift network includes at least two all-pass digital filters which have a phase difference of 90 degrees therebetween. These digital filters are adapted to receive the same signal. Each of the all-pass digital filters has phase characteristics .theta. (.omega.) given by ##EQU1## where T represents a sampling period, P.sub.i a real number indicative of a filter coefficient, .omega. the angular frequency, m a weight variable, n'=n/2 (n=even number), n'=(n+1)/2 (n=odd number), n an order of a 90-degree digital PSN, m being a positive value other than 1, and satisfying .vertline.2m.omega..vertline. / .vertline.P.sub.i .vertline.<1 when .omega. T is sufficiently lower than 1, while satisfying .vertline.-P.sub.i .omega. T.sup.2 .vertline. / 2m<1 when .omega. T is substantially equal to .pi..

Claims14

Dependent claims

A system for controlling a 90-degree phase shift characteristic .theta.'(.omega.)=.theta. a(.omega.)-.theta.b(.omega.) of a 90-degree phase shift network including first and second all-pass digital filters having phase characteristics .theta. a(.omega.) and .theta. b(.omega.), the system comprising:

means for setting a weight variable m and analog transfer functions Ha(s) and Hb(s) of the first and second all-pass digital filters, the weight variable m being a positive value other than 1;
means for transforming the analog transfer functions Ha(s) and Hb(s) set by said setting means to digital transfer functions Ha(z) and Hb(z) by use of a variable bilinear z-transform ##EQU23## and outputting the digital transfer functions Ha(z) and Hb(z);
and means for controlling filter coefficients Pai and Pbi of the first and second all-pass digital filters in accordance with the digital transfer functions Ha(z) and Hb(z),
wherein the weight variable m is within a range which satisfies .vertline.2m.omega..vertline. / .vertline.Pai.vertline.<1 and .vertline.2m.omega..vertline. / .vertline.Pbi.vertline.<1 if .omega. is lower than 1, and within a range which satisfies .vertline.-Pai .omega.T.sup.2 .vertline. / 2m<1 and .vertline.-Pbi.omega.T.sup.2 .vertline. /2m<1 if .omega. T is equal to .pi., where T represents a sampling period, s represents a Laplacian Factor, .omega. represents an angular frequency, and Pai and Pbi represent filter coefficients of the first and second all-pass digital filters.

1 more element

A system for controlling a linearizer including a first all-pass filter, having phase characteristics of .theta. a, for receiving a predetermined input signal;

a second all-pass filter, having phase characteristics of .theta.b, for receiving the predetermined input signal, the phase difference between the first and second all-pass filters satisfying tan ((.theta. a - .theta. b)/2)=.+-.1;
a multiplying circuit for multiplying the output of the first all-pass filter by the output of the second all-pass filter;
a third all-pass filter connected to an output of the first all-pass filter, the third all-pass filter having the same phase characteristics of .theta. a as the first all-pass filter;
and an adding circuit for adding the output of the third all-pass filter to the output of the multiplying circuit, the system comprising:
means for setting a weight variable m and analog transfer functions Ha(s) of the first and third all-pass digital filters and Hb(s) of the second all-pass digital filter, the weight variable m being a positive value other than 1;
means for transforming the analog transfer functions Ha(s) and Hb(s) set by said setting means to digital transfer functions Ha(z) and Hb(z) by use of a variable bilinear z-transform ##EQU29## and outputting the digital transfer functions Ha(z) and Hb(z);
and means for controlling filter coefficients Pai of the first and third all-pass digital filters and Pbi of the second all-pass digital filter in accordance with the digital transfer functions Ha(z) and Hb(z),
wherein the weight variable m is within a range which satisfies .vertline.2m.omega..vertline. / .vertline.Pai.vertline.<1 and .vertline.2m.omega..vertline. / .vertline.Pbi.vertline.<1 if .omega. is lower than 1, and within a range which satisfies .vertline.-Pai.omega.T.sup.2 .vertline. / 2m<1 and .vertline.-Pbi.omega.T.sup.2 .vertline. / 2m<1 if .omega.T is equal to .pi., where T represents a sampling period, s represents a Laplacian Factor, .omega. represents an angular frequency, and Pai represents filter coefficients of the first and third all-pass digital filters and Pbi represents filter coefficients of the second all-pass digital filter.

5 more elements

A system for controlling a linearizer including a first all-pass filter, having phase characteristics of .theta. a, for receiving a predetermined input signal;

a second all-phase filter, having phase characteristics of .theta. b, for receiving the predetermined input signal, the phase difference between the first and second all-pass filters satisfying tan ((.theta. a - .theta. b)/2)=.+-.1;
a multiplying circuit for multiplying the output of the first all-pass filter by the output of the second all-pass filter;
a third all-pass filter connected to an output of the second all-pass filter, the third all-pass filter having the same phase characteristics of .theta. b as the second all-pass filter;
and an adding circuit for adding the output of the third all-pass filter to the output of the multiplying circuit, the system comprising:
means for setting a weight variable m and analog transfer functions Ha(s) of the first all-pass digital filter and Hb(s) of the second and third all-pass digital filters, the weight variable m being a positive value other than 1;
means for transforming the analog transfer functions Ha(s) and Hb(s) set by said setting means to digital transfer functions Ha(z) and Hb(z) by use of a variable bilinear z-transform ##EQU33## and outputting the digital transfer functions Ha(z) and Hb(z);
and means for controlling filter coefficients Pai of the first all-pass digital filter and Pbi of the second and third all-pass digital filters in accordance with the digital transfer functions Ha(z) and Hb(z),
wherein the weight variable m is within a range which satisfies .vertline.2m.omega..vertline. / .vertline.Pai.vertline.<1 and .vertline.2m.omega..vertline. / .vertline.Pbi.vertline.<1 if .omega. is lower than 1, and within a range which satisfies .vertline.-Pai.omega.T.sup.2 .vertline. / 2m<1 and .vertline.-Pbi.omega.T.sup.2 .vertline. / 2m<1 if .omega. T is equal to .pi., where T represents a sampling period, s represents a Laplacian Factor, .omega. represents an angular frequency, and Pai represents filter coefficients of the first all-pass digital filter and Pbi represents filter coefficients of the second and third all-pass digital filters.

5 more elements

Dependencies are inferred from the claim text.