US 6,643,317 B1 · Digital spread spectrum circuit

Abstract

A digital spread spectrum system provides a simple, digital device and method for reducing electromagnetic interference even where a clock signal to the device is rapidly turned on and off. A primary clock signal drives a signal selector. A signal delay is provided in the circuit to provide delayed clock pulse signals. The signal delay detunes the primary clock signal. By repeatedly switching the delay in and out of the clock signal path, a first signal is generated having a frequency at or about the clock signal, and, a second signal is generated which is displaced slightly from the first signal, but still at or about the clock frequency. By repeatedly switching the delay in and out of the primary clock signal path at a rate greater than the frequency of the clock signal, smaller portions of each primary clock pulse may be parsed for subsequent reaggregation to create a spread spectrum clock signal. As a result, a plurality of spread spectrum clock signals at varying frequencies may be created to spread the energy of the signal over a broader spectrum, thereby lowering the signal energy peak to minimize radiation of electromagnetic emissions at undesirable levels.

Claims17

Dependent claims

A spread spectrum circuit for generating a clock output signal with reduced amplitude electromagnetic interference (EMI) spectral components, said spread spectrum circuit comprising:

a clock pulse generator for generating a primary clock signal having a fundamental frequency with a fundamental amplitude, wherein said primary clock signal is comprised of a series of clock pulses and wherein said clock pulses are composed of a plurality of spectral components at differing frequencies, said primary clock signal also having fundamental EMI spectral components at harmonics of said fundamental frequency, said fundamental EMI spectral components each having a fundamental amplitude;
a delay for delaying transmission of said primary clock signal;
a selector for selecting from a plurality of available clock signals;
a controller for driving said selector;
a combiner for combining a selected first clock signal with a selected second clock signal to generate an output clock signal having combined characteristics of said first clock signal and said second clock signal;
and
an aggregator cooperating with said selector and said combiner for generating a spread spectrum clock output signal having a nominal frequency substantially equivalent to said fundamental frequency of said primary clock signal, wherein said nominal frequency includes nominal EMI spectral components at harmonics of said nominal frequency, said nominal EMI spectral components each having a nominal amplitude, and wherein said nominal amplitude is less than said fundamental amplitude.

4 more elements

A method for generating a clock output signal with reduced amplitude electromagnetic interference (EMI) spectral components, said method comprising:

providing a means to generate a series of clock pulses;
generating a series of clock pulses;
digitally modulating the clock pulses by spreading the energy of each clock pulse over a greater bandwidth;
generating a digitally-modulated clock output signal;
providing a means to delay transmittal of a clock pulse or a portion thereof;
providing a means to parse the clock pulse into portions;
providing a means to select from a plurality of delayed and non-delayed clock pulses or portions thereof;
providing a means to combine at least one clock pulse or portion thereof with one or more clock pulses or portions thereof;
providing a means to reaggregate the combined clock pulses or portions thereof;
parsing individual clock pulses into a plurality of portions;
selecting one or more of the clock pulses or portions thereof;
reaggregating the clock pulses or portions thereof;
creating a new series of spread spectrum clock pulses having a nominal frequency and nominal amplitude, wherein said nominal frequency is substantially similar to the fundamental frequency and the nominal amplitude is lower than the fundamental amplitude;
generating a spread spectrum clock signal;
and,
outputting the spread spectrum clock signal to other digital devices to control or synchronize the operation of the digital devices.

13 more elements

Dependencies are inferred from the claim text.

Digital spread spectrum circuit

Life of this patent

Digital spread spectrum circuit

Life of this patent

Abstract

Claims17