Low-noise differential-output capacitor DAC
AssigneeRambus Inc.
InventorShankar Tangirala
Life of this patent
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Abstract
A capacitor-based digital-to-analog-converter produces a level-shifted analog outputs by precharging respective sets of output-generating capacitors to different applied potentials and then floating a common output of the sets of capacitors such that charge is redistributed among the capacitors through the common output to yield, across all the capacitors, a uniform precharge voltage that falls between the different applied potentials.
Claims20
A digital-to-analog converter comprising:
- capacitors having respective inputs and having outputs coupled in common to an output node;
- and
- control circuitry to:
- charge first and second subsets of the capacitors to respective first and second precharge voltages during a precharge interval by coupling the output node to a first voltage source, coupling the inputs of the capacitors of the first subset to a first reference voltage and coupling the inputs of the capacitors of the second subset to a second reference voltage;
- decouple the output node from the first voltage source upon conclusion of the precharge interval;
- and
- after decoupling the output node from the first voltage source, couple the inputs of the capacitors of the first and second subsets to either the first reference voltage or the second reference voltage according to bits of a digital input.
The digital-to-analog converter of 1 wherein the first voltage source is an analog voltage having an amplitude indicated by the digital input.
A method of operation within a digital-to-analog converter having an output node and capacitors with outputs coupled in common to the output node, the method comprising:
- charging first and second subsets of the capacitors to respective first and second precharge
- voltages during a precharge interval, including:
- coupling the output node to a first voltage source,
- coupling inputs of the capacitors of the first subset to a first reference voltage, and
- coupling the inputs of the capacitors of the second subset to a second reference voltage;
- decoupling the output node from the first voltage source upon conclusion of the precharge interval;
- and
- after decoupling the output node from the first voltage source, coupling the inputs of the capacitors of the first and second subsets to either the first reference voltage or the second reference voltage according to bits of a digital input.
An analog-to-digital converter (ADC) comprising:
- a first ADC stage to generate a first digital value in response to a first analog signal;
- a second ADC stage to generate a second digital value in response to a second analog signal;
- and
- a digital-to-analog converter to generate the second analog signal on an output node coupled to the second ADC stage in response to the first digital value and the first analog signal, the digital-to-analog converter including:
- capacitors having respective inputs and having outputs coupled in common to the output node;
- and
- control circuitry to:
- charge first and second subsets of the capacitors to respective first and second precharge voltages during a precharge interval by coupling the first analog signal to the output node, coupling the inputs of the capacitors of the first subset to a first reference voltage and coupling the inputs of the capacitors of the second subset to a second reference voltage;
- decouple the first analog signal from the output node upon conclusion of the precharge interval;
- and
- after decoupling the first analog signal from the output node, couple the inputs of the capacitors of the first and second subsets to either the first reference voltage or the second reference voltage according to bits of the first digital value to produce the second analog voltage on the output node.
Dependencies are inferred from the claim text.