Phase rotator non-linearity reduction
AssigneeRambus Inc.
InventorsMarcus Van Ierssel, Dominic Diclemente
Life of this patent
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Abstract
A phase rotator receives control signals and thermometer coded signals that specifies the phase of an output signal. The phase rotator may be used, for example, by a clock and data recovery (CDR) circuit to continually rotate the phase of a clock to compensate for phase/frequency mismatches between received data and the clock. The control signals determine the phase quadrant (i.e., 0°-90°, 90°-180°, etc.) of the output signal. The thermometer coded signals determine the phase of the output signal within a quadrant by steering a set of bias currents between two or more nodes. The set of bias currents are selected to reduce the non-linearity between the thermometer coded value and the phase of the output signal.
Claims17
An integrated circuit, comprising:
- a phase interpolator configured to receive two or more signals having different phases;
- current source bias circuitry connected to determine respective contributions the two or more signals have to a phase of an output signal, the current source bias circuitry comprising N number of switchable current limiting circuits controllable by an N-bit thermometer code, where N is greater than 3;
- the N number of switchable current circuits to each be biased with respective limited currents controlled by respective current limiting circuits to reduce a non-linearity in a relationship between the thermometer code and the phase of the output signal;
- and,
- the current limiting circuits to be biased by respective nodes of a resistive ladder network, a first current source to draw current from a node of the resistive ladder network that is not at an end of the resistive ladder network.
An integrated circuit, comprising:
- a phase interpolator biased by a selectable current, the phase interpolator configured to receive two or more signals having different phases and to produces an output signal having a phase;
- and,
- digital code to analog current converter circuitry to determine the selectable current corresponding to the digital code, the selectable current provided for a given digital code using a resistive ladder network and to have a non-linear relationship that reduces a non-linearity in a relationship between the digital code and the phase of the output signal, the non-linear relationship to be adjustable by control circuitry that draws current from a node of the resistive ladder network that is not at an end of the resistive ladder network.
A phase rotator circuit, comprising:
- a first adjustable current bias to determine a current flowing from an internal node of a resistive ladder network;
- a plurality of current sources biased by the resistive ladder network, respective currents flowing through the plurality of current sources selectively, based on a digital code, steerable to produce a second current bias and a third current bias;
- and,
- a phase interpolator configured to receive two or more signals having different phases, the second current bias and the third current bias to determine respective contributions the two or more signals have to a phase of an output signal, respective resistances of the resistive ladder network and the adjustable current bias to bias the current sources to at least partially compensate for a non-linear relationship between the phase of the output signal and the digital code.
Dependencies are inferred from the claim text.