System and method for generating shaped noise

• US 8,130,128 B2
• Filed: 03/30/2010
• Issued: 03/06/2012
• Est. Priority Date: 03/30/2010
• Status: Expired due to Fees

• Current Assignee: Silicon Laboratories Incorporated
• Original Assignee: Silicon Laboratories Incorporated
• Inventors: Alderson, Jeff D.
• Primary Examiner(s): Lauture, Joseph
• Application Number:
  US12/798,092
• Publication Number:
  US 20110241919A1
• Time in Patent Office: 707 Days
• Field of Search: 341/152, 341/120, 341/118, 341/143, 375/243, 375/244, 375/245, 375/346, 375/350, 332/107, 332/109
• US Class Current: 341/152
• CPC Class Codes: G06F 1/02 Digital function generators
• CPC Class Codes: G06F 2101/14 Probability distribution functions
• CPC Class Codes: H03F 3/217 Class D power amplifiers; Switching amplifiers
• CPC Class Codes: H03K 3/84 Generating pulses having a predetermined statistical distribution of a parameter, e.g. random pulse generators
• CPC Class Codes: H03K 7/08 Duration or width modulation ; Duty cycle modulation
• CPC Class Codes: H04B 15/04 the interference being caused by substantially sinusoidal oscillations, e.g. in a receiver or in a tape-recorder
• CPC Class Codes: H04B 2215/064 Reduction of clock or synthesizer reference frequency harmonics
• CPC Class Codes: H04B 2215/067 by modulation dispersion
• CPC Class Codes: H04L 25/03828 Arrangements for spectral shaping; Arrangements for providing signals with specified spectral properties partial response systems H04L25/497
• CPC Class Codes: H04L 25/4902 Pulse width modulation; Pulse position modulation

Abstract

In a particular embodiment, a circuit device is disclosed that includes a data generator adapted to output a random pulse sequence having a particular spectral shape. The data generator includes a feedback loop with a transfer function, the output of which may be altered by limiter circuitry to increase stability of the data generator. The circuit device may further include, for example, a pulse edge control circuit to selectively apply a carrier suppression operation to at least one pulse-width modulated (PWM) signal in response to the random pulse sequence to produce at least one modulated PWM output signal. In such an example, the spectral energy associated with a PWM carrier of the modulated PWM output signal at a carrier frequency and associated harmonics is changed such that the modulated PWM output signal has a spectral shape defined by the particular spectral shape.

Claims

1. A circuit device, comprising:

a data generator adapted to output a random pulse sequence having a particular spectral shape, the data generator including a sigma-delta modulator that includes a zero input signal, a random noise signal, a quantizer, a noise transfer function defined within a feedback loop, and limiter circuitry coupled within the feedback loop between the output of the feedback loop and the noise transfer function;

where a feedback value output by the feedback loop of the sigma-delta modulator is subtracted from the zero input signal of the sigma-delta modulator to produce a first result prior to addition of the random noise signal to the first result to produce a second result;

where the second result is provided to the quantizer of the sigma-delta modulator to produce a random pulse sequence at an output of the sigma-delta modulator; and

where the random pulse sequence is subtracted from the first result to produce a feedback result that is provided to the noise transfer function of the sigma-delta modulator.

2. The circuit device of claim 1, wherein the limiter circuitry is configured to limit the absolute value of the output of the noise transfer function.

3. The circuit device of claim 1, wherein the quantizer is configured to produce a random pulse sequence having values of plus or minus one at an output of the sigma-delta modulator;

and wherein the limiter circuitry is configured to limit the absolute value of the output of the noise transfer function to limit the absolute value of an error term in the feedback result that is provided to the noise transfer function.

4. The circuit device of claim 1, wherein the quantizer is configured to produce a random pulse sequence having values of +1 or −

1 at an output of the sigma-delta modulator; and

wherein the limiter circuitry is configured to limit the absolute value of the output of the noise transfer function to a value of +2 or −

2 to limit the absolute value of an error term in the feedback result provided to the noise transfer function to less than or equal to 1.0.

5. The circuit device of claim 1, further comprising:

a pulse edge control circuit to selectively apply a carrier suppression operation to at least one pulse-width modulated (PWM) signal in response to the random pulse sequence to produce at least one modulated PWM output signal; and

where spectral energy associated with a PWM carrier of the modulated PWM output signal at a carrier frequency and associated harmonics is changed such that the modulated PWM output signal has a spectral shape defined by the particular spectral shape.

6. The circuit device of claim 5, wherein the particular spectral shape includes notches at specified frequencies, and wherein the spectral shape of the modulated PWM output signal includes notches at desired frequencies.

7. The circuit device of claim 5, wherein the carrier suppression operation comprises a chop operation that is selectively applied to chop or not chop the at least one PWM input signal with its duty cycle complement PWM signal according to the random pulse sequence.

8. The circuit device of claim 7, wherein the noise transfer function is programmable to create a plurality of spectral shapes, wherein at least one of the plurality of spectral shapes includes one or more notches at desired frequencies.

9. A method comprising:

providing a data generator comprising a sigma-delta modulator that includes a zero input signal, a random noise signal, a quantizer, a noise transfer function defined within a feedback loop, and limiter circuitry coupled within the feedback loop between the output of the feedback loop and the noise transfer function; and

producing a random pulse sequence having a particular spectral shape from the data generator by subtracting a feedback value output by the feedback loop of the sigma-delta modulator from the zero input signal of the sigma-delta modulator to produce a first result prior to adding the random noise signal to the first result to produce a second result, providing the second result to the quantizer of the sigma-delta modulator to produce a random pulse sequence at an output of the sigma-delta modulator, subtracting the random pulse sequence from the first result to produce a feedback result, and providing the feedback result to the noise transfer function of the sigma-delta modulator.

10. The method of claim 9, further comprising limiting the absolute value of the output of the noise transfer function.

11. The method of claim 9, further comprising using the quantizer to produce a random pulse sequence having values of plus or minus one at an output of the sigma-delta modulator;

and limiting the absolute value of the output of the noise transfer function to limit the absolute value of an error term in the feedback result that is provided to the noise transfer function.

12. The method of claim 9, further comprising using the quantizer to produce a random pulse sequence having values of +1 or −

1 at an output of the sigma-delta modulator; and

limiting the absolute value of the output of the noise transfer function to a value of +2 or −

2 to limit the absolute value of an error term in the feedback result provided to the noise transfer function to less than or equal to 1.0.

13. The method of claim 9, further comprising:

receiving at least one pulse-width modulated (PWM) input signal from a PWM source; and

applying a carrier suppression operation to selectively phase shift or to selectively chop the received at least one PWM input signal according to values of the random pulse sequence to produce at least one modulated PWM output signal with a desired spectral shape as defined by the random pulse sequence.

14. The method of claim 9, wherein the particular spectral shape includes one or more notches at selected frequencies.

15. The method of claim 9, further comprising programming the noise transfer function of the data generator to produce the particular spectral shape.

16. The method of claim 9, wherein the at least one modulated PWM output signal has carrier energy that is spread to frequencies other than a carrier frequency and its harmonics.

17. The method of claim 16, further comparing applying the carrier suppression operation by selectively chopping or not chopping the at least one PWM input signal with its duty cycle complement PWM signal according to the random pulse sequence.