Coherent frequency clock generation and spectrum management with non-coherent phase

• US 7,706,484 B2
• Filed: 06/22/2006
• Issued: 04/27/2010
• Est. Priority Date: 06/22/2006
• Status: Expired due to Fees

• Current Assignee: International Business Machines Corporation
• Original Assignee: International Business Machines Corporation
• Inventors: Gilliland, Don A.
• Primary Examiner(s): Ghebretinsae; Temesghen
• Assistant Examiner(s): Parker; Jeffrey
• Application Number:
  US11/425,769
• Publication Number:
  US 20070297550A1
• Time in Patent Office: 1,405 Days
• Field of Search: 375/360, 375/359, 375/354, 375/316, 375/326, 375/325, 375/324, 375/322, 375/338, 375/339, 375/348, 375/347, 375/346, 375/376, 375/375, 375/374, 375/373, 375/368, 375/365, 375/362, 327/144, 327/141, 327/152, 327/153, 327/161, 327/162
• US Class Current: 375/346
• CPC Class Codes: G06F 1/10 Distribution of clock signals , e.g. skew
• CPC Class Codes: H03K 19/00346 Modifications for eliminating interference or parasitic voltages or currents

Abstract

In a method for reducing electromagnetic interference in a clocked circuit, the clock circuit includes at least a first clock signal and a second clock signal. The method detects when a first transition of the first clock signal is substantially aligned with a corresponding second transition of the second clock signal. The second clock signal is delayed by a predetermined amount of time when the first transition is substantially aligned with the second transition.

Claims

1. A method for reducing electromagnetic interference in a clocked circuit, comprising the actions of:

a. generating a base clock signal;

b. generating a first copy of the base clock signal, a second copy of the base clock signal and a third copy of the base clock signal;

c. transmitting the first copy of the base clock signal to a first output;

d. comparing a first transition in the first copy of the base clock signal to a second transition in the second copy of the base clock signal;

e. transmitting the second copy of the base clock signal to a second output when the first transition is not concurrent with the second transition and generating a delayed copy of the second copy of the base clock signal when the first transition is concurrent with the second transition;

f. comparing the first transition in the first copy of the base clock signal to a third transition in the third copy of the base clock signal;

g. transmitting the third copy of the base clock signal to an intermediate node when the first transition is not concurrent with the third transition and generating a delayed copy of the third copy of the base clock signal when the first transition is concurrent with the third transition;

h. comparing a fourth transition in a signal at the second output to a fifth transition in a signal at the intermediate node;

i. transmitting the signal at the intermediate node to a third output when the fourth transition is not concurrent with the fifth transition and generating a delayed copy of the signal at the intermediate node and transmitting the delayed copy of the signal at the intermediate node to the third output when the fourth transition is concurrent with the fifth transition.

2. A clock management circuit, comprising:

a. a base clock signal generator that generates a base clock signal;

b. at least a first direct digital synthesizer responsive to the base clock signal generator and configured to generate a first copy of the base clock signal that is transmitted to a first output, a second direct digital synthesizer responsive to the base clock signal generator and configured to generate a second copy of the base clock signal and a third direct digital synthesizer responsive to the base clock signal generator and configured to generate a third copy of the base clock signal;

c. a first slope detection and comparison circuit that is configured to detect a first transition in the first copy of the base clock signal and a second transition in the second copy of the base clock signal and that is configured to transmit the second copy of the base clock signal to a second output if the first transition is not concurrent with the second transition and that is configured to transmit the second copy of the base clock signal to a delay element configured to transmit a delayed copy of the second copy of the base clock signal to the second output if the first transition is concurrent with the second transition;

d. a second slope detection and comparison circuit that is configured to detect the first transition in the first copy of the base clock signal and a third transition in the third copy of the base clock signal and that is configured to transmit the third copy of the base clock signal to an intermediate node if the first transition is not concurrent with the third transition and that is configured to transmit the third copy of the base clock signal to a delay element configured to transmit a delayed copy of the third copy of the base clock signal to the intermediate node if the first transition is concurrent with the third transition;

e. a third slope detection and comparison circuit that is configured to detect a fourth transition in a signal at the second output to a fifth transition in a signal at the intermediate node and that is configured to transmit the signal from the intermediate node to a third output if the fourth transition is not concurrent with the fifth transition and that is configured to transmit the signal from the intermediate node to a delay element configured to transmit a delayed copy of the signal from the intermediate node to the third output if the fourth transition is concurrent with the fifth transition.

3. The clock management circuit of claim 2, wherein the first slope detection and comparison circuit, the second slope detection and comparison circuit and the third slope detection and comparison circuit each comprise a phase detector.

4. The clock management circuit of claim 2, wherein each delay element comprises a delay line.

5. The clock management circuit of claim 2, wherein each delay element comprises delay gate through which the second clock signal propagates.