US 5,479,125 AGranted

Frequency multiplying clock signal generator

AssigneeZilog, Inc.

InventorJohn Tran

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Abstract

A clock signal generator for creating an output clock signal with fifty percent duty cycle and multiple of the input clock signal frequency allows generation of such a signal independent of input signal frequency and duty cycle. The generator utilizes an adjustable-delay oscillating feedback loop. A serial array of propagating delay elements measure the period of the input clock signal by triggering on successive input clock signal leading edges. This propagation lengthens the oscillating feedback loop until the output signal matches the desired frequency multiple. The feedback loop automatically adjusts according to a predetermined fraction of the period of the input clock signal. A fixed ratio of feedback loop delay to serial array delay ensures an output signal with a desired frequency multiple of the input signal frequency. Incorporation of an inverting logic gate in the oscillating feedback loop ensures a half-wave output clock signal having a fifty percent duty cycle.

A clock signal generator circuit for receiving a first input clock signal having first and second transition edges defining a period and frequency, and generating an output clock signal having a fifty percent duty cycle and a frequency proportional to said input clock signal frequency, said clock signal generator circuit comprising;

a first plurality of serially connected delay elements, each having an input and an output, wherein an input signal received at said input is transmitted as an output signal through said output after being delayed by a first delay period, and each successive one of said first plurality of delay elements receives as its input signal the output signal of a previous one of said first plurality of delay elements;
a plurality of gating elements, each gating element having an input, an output, and a gate control, wherein the input of each of said gating elements is connected to the output of a corresponding one of said first plurality of delay elements, and the outputs of said gating elements are connected to a common node;
an inverter having an input connected to said common node, and an output connected to the input of a first one of said first plurality of delay elements;
an encoder circuit including an input for receiving said input clock signal, a plurality of encoded outputs and a second plurality of serially connected delay elements, each of said second plurality of delay elements having first and second delay inputs and a delay output, wherein a first input signal, responsive to said first transition edge of said input clock signal, received at said first delay input, is delayed by a second delay period and transmitted as an output signal through said delay output, and, until a second input signal responsive to said second transition edge of said input clock signal, is received at said plurality of delay elements through said second delay inputs, each successive one of said second plurality of delay elements receives at its first delay input the output signal of a previous one of said second plurality of delay elements and delays said input signal by said second delay period, and wherein said plurality of encoded outputs is responsive to said delay outputs of said second plurality of delay elements;
and
a decoder circuit having a plurality of inputs respectively connected to said plurality of encoded outputs of said encoder circuit, and a plurality of outputs respectively connected to said gate controls of said plurality of gating elements, wherein said decoder circuit, in response to said encoded outputs, causes only a selected one of said plurality of gating elements to turn on, and said output clock signal to be provided at said output of said inverter after said selected one of said plurality of gating elements is turned on.

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Abstract

Claims10