US5488627A
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US
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Spread spectrum clock generator and associated method
Assignee: Lexmark International Inc
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Filing: 1993-11-29
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Granted: 1996-01-30
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Expires: 2013-11-29
Abstract
Abstract A clock circuit includes an oscillator for generating a reference frequency signal, and a spread spectrum clock generator cooperating with the oscillator for generating a spread spectrum clock output signal having a fundamental frequency and reduced amplitude EMI spectral components at harmonics of the fundamental frequency. The spread spectrum clock generator preferably includes a clock pulse generator for generating a series of clock pulses, and a spread spectrum modulator for frequency modulating the clock pulse generator to broaden and flatten amplitudes of EMI spectral components which would otherwise be produced by the clock pulse generator. The spread spectrum modulator frequency modulates the clock pulses with specific profiles of frequency deviation versus the period of the profile. Electronic devices including the spread spectrum clock circuit and associated method are also disclosed.
Inventors
- 👤 Keith B. Hardin
- 👤 John T. Fessler
- 👤 Donald R. Bush
- 👤 James J. Booth
Bibliographic Details
Application Number
—
Jurisdiction
US
Data Source
google_patents
Last Synchronized
2026-10-28 18:42
CPC Classifications
H; H03; H03K; H03K4/00; H03K4/94; H03C; H03C3/00; H03C3/02; H03C3/09; H03C3/0908; H03C3/0966; H03B; H03B29/00; H03C3/0916; H03C3/0925; H03C3/0941; H03L; H03L7/00; H03L7/06; H03L7/08; H03L7/0805; H03L7/16; H03L7/18; H03L7/197; H04; H04B; H04B2215/00; H04B2215/064; H04B2215/067
Claims Analysis
Total Claims: 39
Claim 1
Independent Claim
312 words
A clock circuit for generating a clock output signal with reduced amplitude electromagnetic interference (EMI) spectral components, said clock circuit comprising: oscillator means for generating a reference frequency signal; and spread spectrum clock generating means cooperating with said oscillator means for generating a spread spectrum clock output signal having a fundamental frequency and reduced amplitude EMI spectral components at harmonics of the fundamental frequency, said spread spectrum clock generating means comprising clock pulse generating means for generating a series of generally rectangularly shaped electrical clock pulses; and spread spectrum modulating means cooperating with said clock pulse generating means for modulating same to broaden and flatten amplitudes of impulse-shaped EMI spectral components which would otherwise be produced by said clock pulse generating means, said spread spectrum modulating means comprising frequency modulating means for frequency modulating said clock pulse generating means, said frequency modulating means comprising profile modulating means for modulating the clock pulse generating means with a periodic waveform having a percentage of frequency deviation profile as a function of percentage of a period (% Period) of the periodic waveform within an envelope defined by predetermined upper and lower bounds, wherein said predetermined upper bound for a second quadrant is defined by F 3 which is equal to ##EQU5## wherein said predetermined lower bound is defined by F 4 which is equal to ##EQU6## wherein for a first quadrant between -25% to 0% Period the lower bound is equal to -F 3 (-% Period) and the upper bound is equal to -F 4 (-% Period); wherein for a third quadrant between 25% to 50% Period the lower bound is equal to F 4 (50-% Period), and the upper bound is equal to F 3 (50-% Period); and wherein for a fourth quadrant the lower bound is equal to -F 3 (% Period-50) and the upper bound is equal to -F 4 (% Period-50).
Claim 2
Dependent Claim
312 words
A clock circuit for generating a clock output signal with reduced amplitude electromagnetic interference (EMI) spectral components, said clock circuit comprising: oscillator means for generating a reference frequency signal; and spread spectrum clock generating means cooperating with said oscillator means for generating a spread spectrum clock output signal having a fundamental frequency and reduced amplitude EMI spectral components at harmonics of the fundamental frequency, said spread spectrum clock generating means comprising clock pulse generating means for generating a series of generally rectangularly shaped electrical clock pulses; and spread spectrum modulating means cooperating with said clock pulse generating means for modulating same to broaden and flatten amplitudes of impulse-shaped EMI spectral components which would otherwise be produced by said clock pulse generating means, said spread spectrum modulating means comprising frequency modulating means for frequency modulating said clock pulse generating means, said frequency modulating means comprising profile modulating means for modulating the clock pulse generating means with a periodic waveform having a percentage of frequency deviation profile as a function of percentage of a period (% Period) of the periodic waveform within an envelope defined by predetermined upper and lower bounds, wherein said predetermined upper bound for a second quadrant is defined by F 3 which is equal to ##EQU5## wherein said predetermined lower bound is defined by F 4 which is equal to ##EQU6## wherein for a first quadrant between -25% to 0% Period the lower bound is equal to -F 3 (-% Period) and the upper bound is equal to -F 4 (-% Period); wherein for a third quadrant between 25% to 50% Period the lower bound is equal to F 4 (50-% Period), and the upper bound is equal to F 3 (50-% Period); and wherein for a fourth quadrant the lower bound is equal to -F 3 (% Period-50) and the upper bound is equal to -F 4 (% Period-50).
Claim 3
Dependent Claim
117 words
A clock circuit according to claim 1 wherein said profile modulating means further comprises means for modulating said clock pulse generating means with a periodic waveform having a percentage of frequency deviation profile as a function of percentage of a period (% Period) of the periodic waveform defined in a second quadrant by F 5 which is equal to 100%(0.45(% Period/25) 3 +0.55(% Period/25)); wherein for a first quadrant between -25% to 0% Period the profile is equal to -F 5 (-% Period); wherein for a third quadrant between 25% to 50% Period the profile is equal to F 5 (50-% Period); and wherein for a fourth quadrant the profile is equal to -F 5 (% Period-50).
Claim 4
Dependent Claim
18 words
A clock circuit according to claim 1 wherein said clock pulse generating means comprises a phase locked loop.
Claim 5
Dependent Claim
24 words
A clock circuit according to claim 3 wherein said frequency modulating means comprises an analog modulating generator operatively connected to said phase locked loop.
Claim 6
Dependent Claim
24 words
A clock circuit according to claim 3 wherein said frequency modulating means comprises a programmable modulating generator operatively connected to said phase locked loop.
Claim 7
Dependent Claim
34 words
A clock circuit according to claim 1 wherein said frequency modulating means comprises means for modulating said clock pulse generating means with a periodic waveform having a period of less than about 500 microseconds.
Claim 8
Dependent Claim
19 words
A clock circuit according to claim 1 wherein said oscillator means comprises a crystal having a predetermined resonant frequency.
Claim 9
Dependent Claim
248 words
A clock circuit for generating a clock output signal with reduced amplitude electromagnetic interference (EMI) spectral components, said clock circuit comprising: oscillator means for generating a reference frequency signal; and spread spectrum clock generating means cooperating with said oscillator means for generating a spread spectrum clock output signal having a fundamental frequency and reduced amplitude EMI spectral components at harmonics of the fundamental frequency, said spread spectrum clock generating means comprising clock pulse generating means for generating a series of clock pulses, and profile modulating means for frequency modulating the clock pulse generating means with a periodic waveform having a percentage of frequency deviation profile as a function of percentage of a period (% Period) of the periodic waveform within an envelope defined by predetermined upper and lower bounds, said predetermined upper bound for a second quadrant is defined by F 3 which is equal to ##EQU7## and said predetermined lower bound is defined by F 4 which is equal to ##EQU8## for a first quadrant between -25% to 0% Period the lower bound is equal to -F 3 (-% Period) and the upper bound is equal to -F 4 (-% Period); for a third quadrant between 25% to 50% Period the lower bound is equal to F 4 (50-% Period), and the upper bound is equal to F 3 (50-% Period); and for a fourth quadrant the lower bound is equal to -F 3 (% Period-50) and the upper bound is equal to -F 4 (% Period-50).
Claim 10
Dependent Claim
248 words
A clock circuit for generating a clock output signal with reduced amplitude electromagnetic interference (EMI) spectral components, said clock circuit comprising: oscillator means for generating a reference frequency signal; and spread spectrum clock generating means cooperating with said oscillator means for generating a spread spectrum clock output signal having a fundamental frequency and reduced amplitude EMI spectral components at harmonics of the fundamental frequency, said spread spectrum clock generating means comprising clock pulse generating means for generating a series of clock pulses, and profile modulating means for frequency modulating the clock pulse generating means with a periodic waveform having a percentage of frequency deviation profile as a function of percentage of a period (% Period) of the periodic waveform within an envelope defined by predetermined upper and lower bounds, said predetermined upper bound for a second quadrant is defined by F 3 which is equal to ##EQU7## and said predetermined lower bound is defined by F 4 which is equal to ##EQU8## for a first quadrant between -25% to 0% Period the lower bound is equal to -F 3 (-% Period) and the upper bound is equal to -F 4 (-% Period); for a third quadrant between 25% to 50% Period the lower bound is equal to F 4 (50-% Period), and the upper bound is equal to F 3 (50-% Period); and for a fourth quadrant the lower bound is equal to -F 3 (% Period-50) and the upper bound is equal to -F 4 (% Period-50).
Claim 11
Dependent Claim
116 words
A clock circuit according to claim 8 wherein said profile modulating means includes means for modulating said clock pulse generating means with a periodic waveform having a percentage of frequency deviation profile as a function of percentage of a period (% Period) of the periodic waveform defined in a second quadrant by F 5 which is equal to 100%(0.45(% Period/25) 3 +0.55(% Period/25)); wherein for a first quadrant between -25% to 0% Period the profile is equal to -F 5 (-% Period); wherein for a third quadrant between 25% to 50% Period the profile is equal to F 5 (50-% Period); and wherein for a fourth quadrant the profile is equal to -F 5 (% Period-50).
Claim 12
Dependent Claim
18 words
A clock circuit according to claim 8 wherein said clock pulse generating means comprises a phase locked loop.
Claim 13
Dependent Claim
24 words
A clock circuit according to claim 10 wherein said profile modulating means comprises an analog modulating generator operatively connected to said phase locked loop.
Claim 14
Dependent Claim
24 words
A clock circuit according to claim 10 wherein said profile modulating means comprises a programmable modulating generator operatively connected to said phase locked loop.
Claim 15
Dependent Claim
34 words
A clock circuit according to claim 8 wherein said profile modulating means comprises means for modulating said clock pulse generating means with the periodic waveform having a period of less than about 500 microseconds.
Claim 16
Dependent Claim
19 words
A clock circuit according to claim 8 wherein said oscillator means comprises a crystal having a predetermined resonant frequency.
Claim 17
Dependent Claim
257 words
A clock circuit for generating a clock output signal with reduced amplitude electromagnetic interference (EMI) spectral components, said clock circuit comprising: clock pulse generating means for generating a series of clock pulses; and spread spectrum modulating means cooperating with said clock pulse generating means for modulating same to broaden and flatten amplitudes of EMI spectral components which would otherwise be produced by said clock pulse generating means, said spread spectrum modulating means comprising frequency modulating means for frequency modulating said clock pulse generating means, said frequency modulating means comprising profile modulating means for modulating the clock pulse generating means with a periodic waveform having a percentage of frequency deviation profile as a function of percentage of a period (% Period) of the periodic waveform within an envelope defined by predetermined upper and lower bounds, wherein said predetermined upper bound for a second quadrant is defined by F 3 which is equal to ##EQU9## wherein said predetermined lower bound is defined by F 4 which is equal to ##EQU10## wherein for a first quadrant between -25% to 0% Period the lower bound is equal to -F 3 (-% Period) and the upper bound is equal to -F 4 (-% Period); wherein for a third quadrant between 25% to 50% Period the lower bound is equal to F 4 (50-% Period), and the upper bound is equal to F 3 (50-% Period); and wherein for a fourth quadrant the lower bound is equal to -F 3 (% Period-50) and the upper bound is equal to -F 4 (% Period-50).
Claim 18
Dependent Claim
257 words
A clock circuit for generating a clock output signal with reduced amplitude electromagnetic interference (EMI) spectral components, said clock circuit comprising: clock pulse generating means for generating a series of clock pulses; and spread spectrum modulating means cooperating with said clock pulse generating means for modulating same to broaden and flatten amplitudes of EMI spectral components which would otherwise be produced by said clock pulse generating means, said spread spectrum modulating means comprising frequency modulating means for frequency modulating said clock pulse generating means, said frequency modulating means comprising profile modulating means for modulating the clock pulse generating means with a periodic waveform having a percentage of frequency deviation profile as a function of percentage of a period (% Period) of the periodic waveform within an envelope defined by predetermined upper and lower bounds, wherein said predetermined upper bound for a second quadrant is defined by F 3 which is equal to ##EQU9## wherein said predetermined lower bound is defined by F 4 which is equal to ##EQU10## wherein for a first quadrant between -25% to 0% Period the lower bound is equal to -F 3 (-% Period) and the upper bound is equal to -F 4 (-% Period); wherein for a third quadrant between 25% to 50% Period the lower bound is equal to F 4 (50-% Period), and the upper bound is equal to F 3 (50-% Period); and wherein for a fourth quadrant the lower bound is equal to -F 3 (% Period-50) and the upper bound is equal to -F 4 (% Period-50).
Claim 19
Dependent Claim
115 words
A clock circuit according to claim 15 wherein said profile modulating means further comprises means for modulating said clock pulse generating means with a periodic waveform having a percentage of frequency deviation profile as a function of percentage of a period (% Period) of the periodic waveform defined in a second quadrant by F 5 which is equal to 100%(0.45(% Period/25) 3 +0.55(% Period/25)); wherein for a first quadrant between -25% to 0% Period the profile is equal to -Fs(-% Period); wherein for a third quadrant between 25% to 50% Period the profile is equal to F 5 (50-% Period); and wherein for a fourth quadrant the profile is equal to -F 5 (% Period-50).
Claim 20
Dependent Claim
246 words
An electronic device having reduced amplitude electromagnetic interference (EMI) spectral components, said electronic device comprising: spread spectrum clock generating means for generating a spread spectrum clock output signal having a fundamental frequency and reduced amplitude EMI spectral components at harmonics of the fundamental frequency, said spread spectrum clock generating means comprising profile modulating means for frequency modulating a series of clock pulses with a periodic waveform having a percentage of frequency deviation profile as a function of percentage of a period (% Period) of the periodic waveform within an envelope defined by predetermined upper and lower bounds, wherein said predetermined upper bound for a second quadrant is defined by F 3 which is equal to ##EQU11## wherein said predetermined lower bound is defined by F 4 which is equal to ##EQU12## wherein for a first quadrant between -25% to 0% Period the lower bound is equal to -F 3 (-% Period) and the upper bound is equal to -F 4 (-% Period); wherein for a third quadrant between 25% to 50% Period the lower bound is equal to F 4 (50-% Period), and the upper bound is equal to F 3 (50-% Period); and wherein for a fourth quadrant the lower bound is equal to -F 3 (% Period-50) and the upper bound is equal to -F 4 (% Period 50); and a digital circuit connected to said spread spectrum clock generating means and having a clock input driven by the spread spectrum clock output signal.
Claim 21
Dependent Claim
246 words
An electronic device having reduced amplitude electromagnetic interference (EMI) spectral components, said electronic device comprising: spread spectrum clock generating means for generating a spread spectrum clock output signal having a fundamental frequency and reduced amplitude EMI spectral components at harmonics of the fundamental frequency, said spread spectrum clock generating means comprising profile modulating means for frequency modulating a series of clock pulses with a periodic waveform having a percentage of frequency deviation profile as a function of percentage of a period (% Period) of the periodic waveform within an envelope defined by predetermined upper and lower bounds, wherein said predetermined upper bound for a second quadrant is defined by F 3 which is equal to ##EQU11## wherein said predetermined lower bound is defined by F 4 which is equal to ##EQU12## wherein for a first quadrant between -25% to 0% Period the lower bound is equal to -F 3 (-% Period) and the upper bound is equal to -F 4 (-% Period); wherein for a third quadrant between 25% to 50% Period the lower bound is equal to F 4 (50-% Period), and the upper bound is equal to F 3 (50-% Period); and wherein for a fourth quadrant the lower bound is equal to -F 3 (% Period-50) and the upper bound is equal to -F 4 (% Period 50); and a digital circuit connected to said spread spectrum clock generating means and having a clock input driven by the spread spectrum clock output signal.
Claim 22
Dependent Claim
61 words
An electronic device according to claim 17 wherein said spread spectrum clock generating means comprises: clock pulse generating means for generating a series of clock pulses; and spread spectrum modulating means cooperating with said clock pulse generating means for modulating same to broaden and flatten amplitudes of EMI spectral components which would otherwise be produced by said clock pulse generating means.
Claim 23
Dependent Claim
117 words
A clock circuit according to claim 18 wherein said profile modulating means further comprises means for modulating said clock pulse generating means with a periodic waveform having a percentage of frequency deviation profile as a function of percentage of a period (% Period) of the periodic waveform defined in a second quadrant by F 5 which is equal to 100%(0.45(% Period/25) 3 +0.55(% Period/25)); wherein for a first quadrant between -25% to 0% Period the profile is equal to -F 5 (-% Period); wherein for a third quadrant between 25% to 50% Period the profile is equal to F 5 (50-% Period); and wherein for a fourth quadrant the profile is equal to -F 5 (% Period-50).
Claim 24
Dependent Claim
18 words
An electronic device according to claim 18 wherein said clock pulse generating means comprises a phase locked loop.
Claim 25
Independent Claim
222 words
A method for generating a clock output signal with reduced amplitude electromagnetic interference (EMI) spectral components, said method comprising the steps of: generating a series of clock pulses; and spread spectrum modulating the series of clock pulses to broaden and flatten amplitudes of EMI spectral components which would otherwise be produced along with the series of clock pulses by frequency modulating the series of clock pulses with a periodic waveform having a percentage of frequency deviation profile as a function of percentage of a period (% Period) of the periodic waveform within an envelope defined by predetermined upper and lower bounds, wherein the predetermined upper bound for a second quadrant is defined by which is equal to ##EQU13## wherein the predetermined lower bound is defined by F 4 which is equal to ##EQU14## wherein for a first quadrant between -25% to 0% Period the lower bound is equal to -F 3 (-% Period) and the upper bound is equal to -F 4 (-% Period); wherein for a third quadrant between 25% to 50% Period the lower bound is equal to F 4 (50-% Period), and the upper bound is equal to F 3 (50-% Period); and wherein for a fourth quadrant the lower bound is equal to -F 3 (% Period-50) and the upper bound is equal to -F 4 (% Period-50).
Claim 26
Independent Claim
222 words
A method for generating a clock output signal with reduced amplitude electromagnetic interference (EMI) spectral components, said method comprising the steps of: generating a series of clock pulses; and spread spectrum modulating the series of clock pulses to broaden and flatten amplitudes of EMI spectral components which would otherwise be produced along with the series of clock pulses by frequency modulating the series of clock pulses with a periodic waveform having a percentage of frequency deviation profile as a function of percentage of a period (% Period) of the periodic waveform within an envelope defined by predetermined upper and lower bounds, wherein the predetermined upper bound for a second quadrant is defined by which is equal to ##EQU13## wherein the predetermined lower bound is defined by F 4 which is equal to ##EQU14## wherein for a first quadrant between -25% to 0% Period the lower bound is equal to -F 3 (-% Period) and the upper bound is equal to -F 4 (-% Period); wherein for a third quadrant between 25% to 50% Period the lower bound is equal to F 4 (50-% Period), and the upper bound is equal to F 3 (50-% Period); and wherein for a fourth quadrant the lower bound is equal to -F 3 (% Period-50) and the upper bound is equal to -F 4 (% Period-50).
Claim 27
Dependent Claim
57 words
A method according to claim 21 wherein the step of generating the spread spectrum clock output signal comprises the steps of: generating a series of clock pulses; and spread spectrum modulating the series of clock pulses to broaden and flatten amplitudes of EMI spectral components which would otherwise be produced along with the series of clock pulses.
Claim 28
Dependent Claim
123 words
A method according to claim 22 wherein the step of frequency modulating the series of clock pulses with a periodic waveform comprises modulating the series of clock pulses with a periodic waveform having a percentage of frequency deviation profile as a function of percentage of a period (% Period) of the periodic waveform defined in a second quadrant by F 5 which is equal to 100%(0.45(% Period/25) 3 +0.55(% Period/25)); wherein for a first quadrant between -25% to 0% Period the profile is equal to -F 5 (-% Period); wherein for a third quadrant between 25% to 50% Period the profile is equal to F 5 (50-% Period); and wherein for a fourth quadrant the profile is equal to -F 5 (% Period-50).
Claim 29
Dependent Claim
32 words
A method according to claim 23 wherein the step of frequency modulating comprises modulating the series of clock pulses with a periodic waveform having a period of less than about 500 microseconds.
Claim 30
Dependent Claim
203 words
A clock circuit having reduced amplitude electromagnetic interference (EMI) spectral components, said clock circuit comprising: spread spectrum clock generating means for generating a spread spectrum clock output signal having a fundamental frequency and reduced amplitude EMI spectral components at harmonics of the fundamental frequency; said spread spectrum clock generating means comprising profile modulating means for frequency modulating a series of clock pulses with a periodic waveform having a percentage of frequency deviation profile as a function of percentage of a period (% Period) of the periodic waveform defined in a first quadrant between -25% to 0% Period by a predetermined function which is generally negative, increasing and has a concave downward shape; wherein the periodic waveform is defined in a second quadrant between 0% to 25% Period by a predetermined function which is generally positive, increasing and has a concave upward shape; wherein the periodic waveform is defined in a third quadrant between 25% to 50% Period by a predetermined function which is generally positive, decreasing and has a concave upward shape; and wherein the periodic waveform is defined in a fourth quadrant between 50% to 75% Period by a predetermined function which is generally negative, decreasing and has a concave downward shape.
Claim 31
Dependent Claim
203 words
A clock circuit having reduced amplitude electromagnetic interference (EMI) spectral components, said clock circuit comprising: spread spectrum clock generating means for generating a spread spectrum clock output signal having a fundamental frequency and reduced amplitude EMI spectral components at harmonics of the fundamental frequency; said spread spectrum clock generating means comprising profile modulating means for frequency modulating a series of clock pulses with a periodic waveform having a percentage of frequency deviation profile as a function of percentage of a period (% Period) of the periodic waveform defined in a first quadrant between -25% to 0% Period by a predetermined function which is generally negative, increasing and has a concave downward shape; wherein the periodic waveform is defined in a second quadrant between 0% to 25% Period by a predetermined function which is generally positive, increasing and has a concave upward shape; wherein the periodic waveform is defined in a third quadrant between 25% to 50% Period by a predetermined function which is generally positive, decreasing and has a concave upward shape; and wherein the periodic waveform is defined in a fourth quadrant between 50% to 75% Period by a predetermined function which is generally negative, decreasing and has a concave downward shape.
Claim 32
Dependent Claim
38 words
A clock circuit according to claim 25 wherein said spread spectrum clock generating means comprises clock pulse generating means for generating the series of clock pulses, and wherein said clock pulse generating means comprises a phase locked loop.
Claim 33
Dependent Claim
26 words
A clock circuit according to claim 26 wherein said spread spectrum clock generating means comprises an analog modulating generator operatively connected to said phase locked loop.
Claim 34
Dependent Claim
26 words
A clock circuit according to claim 26 wherein said spread spectrum clock generating means comprises a programmable modulating generator operatively connected to said phase locked loop.
Claim 35
Dependent Claim
36 words
A clock circuit according to claim 25 wherein said spread spectrum clock generating means comprises means for modulating said clock pulse generating means with a periodic waveform having a period of less than about 500 microseconds.
Claim 36
Dependent Claim
224 words
An electronic device having reduced amplitude electromagnetic interference (EMI) spectral components, said electronic device comprising: spread spectrum clock generating means for generating a spread spectrum clock output signal having a fundamental frequency and reduced amplitude EMI spectral components at harmonics of the fundamental frequency; said spread spectrum clock generating means comprising profile modulating means for frequency modulating a series of clock pulses with a periodic waveform having a percentage of frequency deviation profile as a function of percentage of a period (% Period) of the periodic waveform defined in a first quadrant between -25% to 0% Period by a predetermined function which is generally negative, increasing and has a concave downward shape; wherein the periodic waveform is defined in a second quadrant between 0% to 25% Period by a predetermined function which is generally positive, increasing and has a concave upward shape; wherein the periodic waveform is defined between 25% to 50% Period by a predetermined function which is generally positive, decreasing and has a concave upward shape; and wherein the periodic waveform is defined in a fourth quadrant between 50% to 75% Period by a predetermined function which is generally negative, decreasing and has a concave downward shape; and a digital circuit connected to said spread spectrum clock generating means and having a clock input driven by the spread spectrum clock output signal.
Claim 37
Dependent Claim
224 words
An electronic device having reduced amplitude electromagnetic interference (EMI) spectral components, said electronic device comprising: spread spectrum clock generating means for generating a spread spectrum clock output signal having a fundamental frequency and reduced amplitude EMI spectral components at harmonics of the fundamental frequency; said spread spectrum clock generating means comprising profile modulating means for frequency modulating a series of clock pulses with a periodic waveform having a percentage of frequency deviation profile as a function of percentage of a period (% Period) of the periodic waveform defined in a first quadrant between -25% to 0% Period by a predetermined function which is generally negative, increasing and has a concave downward shape; wherein the periodic waveform is defined in a second quadrant between 0% to 25% Period by a predetermined function which is generally positive, increasing and has a concave upward shape; wherein the periodic waveform is defined between 25% to 50% Period by a predetermined function which is generally positive, decreasing and has a concave upward shape; and wherein the periodic waveform is defined in a fourth quadrant between 50% to 75% Period by a predetermined function which is generally negative, decreasing and has a concave downward shape; and a digital circuit connected to said spread spectrum clock generating means and having a clock input driven by the spread spectrum clock output signal.
Claim 38
Independent Claim
207 words
A method for generating a clock output signal with reduced amplitude electromagnetic interference (EMI) spectral components, said method comprising the steps of: generating a series of clock pulses; and spread spectrum modulating the series of clock pulses to broaden and flatten amplitudes of EMI spectral components which would otherwise be produced along with the series of clock pulses by frequency modulating the series of clock pulses with a periodic waveform having a percentage of frequency deviation profile as a function of percentage of a period (% Period) of the periodic waveform defined in a first quadrant between -25% to 0% Period by a predetermined function which is generally negative, increasing and has a concave downward shape; wherein the periodic waveform is defined in a second quadrant between 0% to 25% Period by a predetermined function which is generally positive, increasing and has a concave upward shape; wherein the periodic waveform is defined in a third quadrant between 25% to 50% Period by a predetermined function which is generally positive, decreasing and has a concave upward shape; and wherein the periodic waveform is defined in a fourth quadrant between 50% to 75% Period by a predetermined function which is generally negative, decreasing and has a concave downward shape.
Claim 39
Independent Claim
207 words
A method for generating a clock output signal with reduced amplitude electromagnetic interference (EMI) spectral components, said method comprising the steps of: generating a series of clock pulses; and spread spectrum modulating the series of clock pulses to broaden and flatten amplitudes of EMI spectral components which would otherwise be produced along with the series of clock pulses by frequency modulating the series of clock pulses with a periodic waveform having a percentage of frequency deviation profile as a function of percentage of a period (% Period) of the periodic waveform defined in a first quadrant between -25% to 0% Period by a predetermined function which is generally negative, increasing and has a concave downward shape; wherein the periodic waveform is defined in a second quadrant between 0% to 25% Period by a predetermined function which is generally positive, increasing and has a concave upward shape; wherein the periodic waveform is defined in a third quadrant between 25% to 50% Period by a predetermined function which is generally positive, decreasing and has a concave upward shape; and wherein the periodic waveform is defined in a fourth quadrant between 50% to 75% Period by a predetermined function which is generally negative, decreasing and has a concave downward shape.
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