Method and apparatus for reducing switching noise in a system-on-chip (SoC) integrated circuit including an analog-to-digital converter (ADC)
First Claim
1. An integrated circuit, comprising:
- an analog-to-digital converter for receiving an analog input signal and providing a digital output, wherein a discrete-time sampling circuit of the analog-to-digital converter is responsive to a first clock signal to sample the analog input signal;
a digital logic circuit for performing processing operations within the integrated circuit, wherein the digital logic circuit is responsive to a second clock signal to cause transitions of logic within the digital logic circuit; and
a clock generator circuit for receiving a master clock signal and providing the first clock signal and the second clock signal as frequency divisions of the master clock signal, wherein the clock generator circuit includes a first clock divider for generating the first clock signal from the master clock signal and a second clock divider for generating the second clock signal from the master clock signal, and wherein the clock generator circuit adjusts an edge relationship between the first clock signal and the second clock signal such that transitions of the second clock signal do not occur near critical sampling edges of the first clock signal by presetting the first clock divider or the second clock divider with an offset value, whereby sampling error in the analog-to-digital converter due to transition noise coupled from the digital logic circuit is substantially eliminated.
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Abstract
A method and apparatus for reducing switching noise in a system-on-chip (SoC) integrated circuit including an analog to digital converter (ADC) provides for reduced noise in the ADC conversions. Sampling circuits of the ADC are operated by sampling clock signals and digital circuits and other noise-generating circuits such as power converters, are operated by digital circuit clock signals. Both sets of clock signals are derived from the same master clock by a clock generator circuit, but an offset is applied in the clock generator circuit to move the edges of the digital circuit clock signals away from critical sampling intervals corresponding to edges of the sampling clocks. In one embodiment, the offset is applied by a processor core that forms part of the digital circuits by setting a value in the clock generator, which the clock generator then loads into the divider after halting the clock to the digital circuits.
25 Citations
18 Claims
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1. An integrated circuit, comprising:
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an analog-to-digital converter for receiving an analog input signal and providing a digital output, wherein a discrete-time sampling circuit of the analog-to-digital converter is responsive to a first clock signal to sample the analog input signal; a digital logic circuit for performing processing operations within the integrated circuit, wherein the digital logic circuit is responsive to a second clock signal to cause transitions of logic within the digital logic circuit; and a clock generator circuit for receiving a master clock signal and providing the first clock signal and the second clock signal as frequency divisions of the master clock signal, wherein the clock generator circuit includes a first clock divider for generating the first clock signal from the master clock signal and a second clock divider for generating the second clock signal from the master clock signal, and wherein the clock generator circuit adjusts an edge relationship between the first clock signal and the second clock signal such that transitions of the second clock signal do not occur near critical sampling edges of the first clock signal by presetting the first clock divider or the second clock divider with an offset value, whereby sampling error in the analog-to-digital converter due to transition noise coupled from the digital logic circuit is substantially eliminated. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11)
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12. A method of reducing noise in an integrated circuit having a discrete time sampling analog-to-digital converter and digital logic circuit, comprising:
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generating a first clock signal and a second clock signal from a master clock signal; clocking a discrete time sampling circuit of the analog-to-digital converter with the first clock signal; clocking the digital logic circuit with the second clock signal; and adjusting an edge relationship between the second clock signal and the first clock signal by setting an offset of a divider that generates the second clock signal, such that transitions of the second clock signal do not occur near critical sampling edges of the first clock signal, whereby sampling error in the analog-to-digital converter due to transition noise coupled from the digital logic circuit is substantially eliminated. - View Dependent Claims (13, 14, 15)
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- 16. An analog-to-digital converter integrated circuit including a digital processing circuit, an analog sampling circuit, and a clock generator for generating digital clock signals for the digital processing circuit and sampling clock signals to the analog sampling circuit, wherein the clock generator circuit adjusts a delay of the digital clock signals by programming an offset of a divider within the clock generator that generates the digital clock signals such that edges of the digital clock signal are away from critical sampling edges of the sampling clock signals.
Specification