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# High Resolution Digitally Programmable Period Synthesizer

IP.com Disclosure Number: IPCOM000085461D
Original Publication Date: 1976-Apr-01
Included in the Prior Art Database: 2005-Mar-02
Document File: 2 page(s) / 46K

IBM

## Related People

Chang, YE: AUTHOR [+2]

## Abstract

The circuit depicted in the drawing employs a phase-locked loop and volt age-controlled oscillator (VCO) to provide an output frequency that is programmable in fixed increments of time, that is, the clock period is programmable with high resolution. The basic block diagram is shown in Fig. 1.

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High Resolution Digitally Programmable Period Synthesizer

The circuit depicted in the drawing employs a phase-locked loop and volt age-controlled oscillator (VCO) to provide an output frequency that is programmable in fixed increments of time, that is, the clock period is programmable with high resolution. The basic block diagram is shown in Fig. 1.

In this arrangement, the period of the reference clock is multiplied by the digital number N and the period T(out) is a multiple of T(REF). The programmable resolution is limited to the highest frequency practically attainable in the programmable counter.

In order to obtain better resolution, the concept is further extended as shown in Fig. 2.

The output frequency of the VC0 is divided down by a fixed count M, where it goes to the phase detector for comparison to the period N x T(REF). When phase lock is achieved, the VCO provides an output period such that: M x T(OUT) = N x T(REF) or:

T(OUT) = N over M x T(REF).

Since M is a fixed number, the programming resolution of the output period is T(REF)/M.

The above circuit may be readily implemented with the following parameters: T(REF) = 10 nsec (F(REF) = 100 MHZ)

M = 100

N = 50 to 100 (programmable).

This provides a resolution = T(REF) over M = 10/100 = 0.1 nsec.

The output period is programmable from 5.0 nsec (200 MHZ) to 10.0 nsec (100 MHZ) in steps of 100 picoseconds.

Reference is made to U. S. Patent No. 3,913,021, entitled "High Resolution Digitally Programmable Elec...