Telecommunications – Receiver or analog modulated signal frequency converter – Noise or interference elimination
Utility Patent
1997-08-04
2001-01-02
Eisenzopf, Reinhard J. (Department: 2745)
Telecommunications
Receiver or analog modulated signal frequency converter
Noise or interference elimination
C455S310000
Utility Patent
active
06169889
ABSTRACT:
RELATED APPLICATIONS
Application Ser. No. 08/760016, filed Dec. 4, 1996 by Servilio, entitled “ELECTRONIC DEVICE FOR GENERATING A SPREAD SPECTRUM CLOCK SIGNAL FOR USE IN COMMUNICATIONS BETWEEN DEVICE COMPONENTS”
FIELD OF THE INVENTION
This invention relates in general to clock and data signals used in digital circuits of electronic devices, and more specifically to the pulse characteristics of clock and data signals used in the digital circuits.
BACKGROUND OF THE INVENTION
Radio communication devices, such as portable messaging units, typically receive radio signals and decode messages included in the signals. The messages are then processed by circuits, such as decoders, processors, and memory circuits. Within radio communication devices and other electronic devices, circuits can be coupled by serial or parallel interfaces, each of which includes one or more digital lines. Each data line couples a digital signal made up of pulses that are clocked by a clock signal. The clock signal is derived from a reference signal generated by an oscillator. The reference signal is typically divided down into other, slower signals to clock some of the serial or parallel interfaces which operate at speeds slower than the reference signal; for example, a serial communications interface.
When a radio signal is received by a radio communication device which includes digital information, informational portions of the radio frequency spectrum exist within the receiver at a carrier frequency, and can exist at other frequencies, such as an intermediate frequency (IF). Because the serial and parallel interfaces have commonly been driven by clock signals which are periodic square wave signals, high energy harmonics characterized as radio frequency interference (RFI) have typically been generated by these signals. When these harmonics appear in an informational part of the frequency spectrum, they can cause interference problems, resulting in missed signals. Interference is commonly dealt with by radio frequency shielding or attempting to select a frequency of the master device to generate the reference clock signal such that the reference clock signal and other clock signals derived from it have harmonics that minimally interfere with the informational portions of the radio frequency spectrum. However, this method becomes very complex in a radio communication device having multiple clock signals that potentially interfere with the radio circuitry.
Thus, what is needed is a way to provide digital signals that further minimize RFI emissions in an electronic device, while maintaining average clock frequencies that are as high as possible.
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IEEE International Symposium on Electromagnetic Compatibility, 1997, Keith B. Hardin et al., “Design Considerations of Phase-Locked Loop Systems for Spread Spectrum Clock Generation Compatibility,” pp. 302-307.
Using Spread Spectrum in ICS Products, Integrated Circuit Systems, San Jose, California, Application Note, date unknown, 9 pages.
Imad Kobeissi,Noise Reduction Techniques for Microcontroller-Based System, Motorola Semiconductor Application Note, Motorola, Inc., 1997.
Callaway, Jr. Edgar Herbert
DeLuca Michael J.
Servilio Mark L.
Aoki Makoto
Eisenzopf Reinhard J.
Lamb James A.
Motorola
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