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Multiplexer-related

Micro-time-and-phase-stepper

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Micro time and phase stepper

Details

Inventors: Nardin, Roy;
Assignee: ILC Data Device Corporation (Bohemia, NY)
Primary Examiner: Grimm; Siegfried H.
Assistant Examiner:
Attorney, Agent or Firm: Weinstein & Sutton

A digital time phase shifter for shifting a signal in very precise increments and which performs the steps of: mixing a reference frequency signal with the signal to be time or phase delayed for generating an intermediate frequency signal; selectively delaying (i.e. advancing or retarding) the intermediate frequency signal; and mixing the delayed intermediate frequency signal and reference signal developing an output signal whose frequency is an integer multiple or sub-multiple of the input signal frequency and whose phase delay is proportional to the ratio of the intermediate signal and input signal frequencies. Small delay increments are obtained by judicious selection of the reference frequency. The output frequency may be slowly delayed relative to the input frequency by repeating the delay step. The phase shifter employs a pair of phase-locked loops, digital mixing circuits and a programmable delay generator. The input signal and reference signal are mixed developing an intermediate frequency signal, having a delay determined by the setting of the programmable input. One phase-locked loop and mixer develop said reference signal. The other phase-locked loop and mixer generate the output signal, which is time or phase delayed by increments proportional to the ratio of said intermediate signal and said input signal frequencies.

DETAILED DESCRIPTION OF THE INVENTION The present invention utilizes the principle of multiplication of trigonometric functions; namely, cosine waves.
FIG.
1 shows a simplified block diagram of a micro time and phase stepper apparatus 10 which illustrates the principles of the present invention.
As shown in FIG.
1, the micro time and phase stepper 10 employs a first mixer 11 which accepts signals respectively having an input frequency .
omega.
.
sub.
IN at its input 11a and an offset frequency .
omega.
.
sub.
1 at its input 11b, to produce an intermediate frequency signal .
omega.
.
sub.
IF at its output 11c whose frequency is equal to the difference between the frequency of the input signal and the frequency of the offset signal.
The intermediate frequency signal is then delayed in time by a programmable delay line 12, the time delay imparting a phase shift, .
+-.
.
theta.
to the intermediate frequency applied to input 12a, said delayed signal appearing at output 12b.
The phase shifted (i.
e.
delayed) intermediate frequency is then mixed with the offset frequency .
omega.
.
sub.
1 by means of a mixer 13 receiving the offset frequency .
omega.
.
sub.
1 at its input 13a and the delayed intermediate frequency at its input 13b.
Mixer 13 produces a sum frequency which is equal to the input frequency .
omega.
.
sub.
IN with the phase shift of .
+-.
.
DELTA.
.
theta.
at output 13c.
The phase shift corresponds to a time delay (or advance) of the output signal with respect to the input.
This concept will now be clarified by a mathematical analysis as follows: The output of mixer 11 is described mathematically in equation (4) as follows: COS .
omega.
.
sub.
IN t COS .
omega.
.
sub.
1 t=COS (.
omega.
.
sub.
IN +.
omega.
.
sub.
1)t+COS (.
omega.
.
sub.
IN -.
omega.
.
sub.
1)t (4) Only the cosine term representing the difference is of interest.
Thus, .
omega.
.
sub.
IF =COS (.
omega.
.
sub.
IN -.
omega.
.
sub.
1)t (5) The intermediate frequency is passed through the programmable delay line 12 whereby equation (5) is modified in a manner set forth by equation (6); namely,

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