Methods and circuits for slew-rate calibration
AssigneeRambus Inc.
InventorCosmin Iorga
Life of this patent
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Abstract
Described is an integrated circuit with a driving amplifier that transmits a signal over a link (e.g. a wire) by raising and lowering a voltage on the link. A reference oscillator provides an error measure for the rate at which the voltage transitions between voltages, the slew rate. Slew-rate calibration circuitry adjusts the driving amplifier responsive to the error measure.
Claims19
An integrated circuit (IC) comprising:
- a first transmitter having a first input node to receive a first input signal having first input-signal transitions;
- a first multiphase generator coupled to the first input node to receive the first input signal, the first multiphase generator to issue first instances of the first input signal separated by a first phase offset;
- a first oscillator to issue a first clock signal of a first clock frequency proportional to the first phase offset,
- a second transmitter having a second input node to receive a second input signal having second input-signal transitions;
- a second multiphase generator coupled to the second input node to receive the second input-signal, the second multiphase generator to issue second instances of the second input signal separated by a second phase offset;
- a second oscillator to issue a second clock signal of a second clock frequency proportional to the second phase offset, and
- computation circuitry having:
- a first computation input coupled to the first oscillator to receive the first clock signal;
- a first computation output coupled to the first multiphase generator, the computation circuitry to issue a first slew-rate calibration signal to adjust the first phase offset responsive to the first clock signal;
- a second computation input coupled to the second oscillator to receive the second clock signal;
- and
- a second computation output coupled to the second multiphase generator, the computation circuitry to issue a second slew-rate calibration signal to adjust the second phase offset responsive to the second clock signal.
A method for calibrating a slew rate of a signal from a transmitter, the transmitter comprising parallel delay elements conveying an output signal to a drive element, the method comprising:
- deriving an impedance-calibration signal from a replica of the drive element;
- deriving a clock signal from a ring of replicas of the delay elements;
- calculating a slew code from the impedance-calibration signal and the clock signal;
- and
- adjusting the parallel delay elements responsive to the slew code.
A transmitter for transmitting an output signal, the transmitter comprising:
- a drive element;
- a drive-element replica of the drive element;
- a delay element;
- a ring of delay-element replicas of the delay element;
- and
- means for calculating a slew code from drive-element replica and the delay-element replicas.
Dependencies are inferred from the claim text.