Apparatus and method for calibrating the frequency of a clock and data recovery circuit
First Claim
1. An integrated circuit including a clock and data recovery (CDR) circuit, the CDR circuit generating a clock signal based on an input data signal having a period 2τ
- and including a plurality of data state transitions, the CDR circuit comprising;
a first delay arrangement for generating a gating signal of duration τ
based on the data state transitions of the input data signal, wherein the first delay arrangement includes a first delay element;
a gated voltage-controlled oscillator coupled to the first delay arrangement in such a way that the gating signal enables the gated voltage-controlled oscillator, wherein the gated voltage-controlled oscillator, when enabled, generates the clock signal, wherein the generated clock signal has a duration τ and
is synchronized to the center of the data state transitions of the input data signal,wherein the gated voltage-controlled oscillator includes a first frequency control loop that continually calibrates the frequency of the gated voltage-controlled oscillator to generate the clock signal with the duration τ
, and delays the generated clock signal in such a way that the generated clock signal is synchronized to the center of the data state transitions of the input data signal; and
a secondary loop coupled to the first frequency control loop of the gated voltage-controlled oscillator and coupled to the first delay element of the first delay arrangement, wherein the secondary loop includes a frequency detector that tunes the first delay element and tunes the first frequency control loop of the gated voltage-controlled oscillator based on the frequency difference between a recovered clock signal output from the gated voltage-controlled oscillator and an output frequency of a phase locked loop coupled to the frequency detector.
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Abstract
Embodiments of the invention include an apparatus and method for continuously calibrating the frequency of a clock and data recovery (CDR) circuit. The apparatus includes a delay arrangement that generates a gating signal, and a gated voltage-controlled oscillator that is enabled by the gating signal. The gated voltage-controlled oscillator generates a recovered clock signal that is based on the data signal input to the CDR circuit. The apparatus also includes a frequency control loop that continuously calibrates the gated voltage-controlled oscillator in such a way that the frequency of the clock signal generated by the gated voltage-controlled oscillator continues to be one half of the period of the data bits in the input data signal and the clock signal remains synchronized to the center of the data state transitions of the input data signal. Alternatively, a secondary frequency control loop adjusts the amount of delay in the frequency control loop.
63 Citations
21 Claims
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1. An integrated circuit including a clock and data recovery (CDR) circuit, the CDR circuit generating a clock signal based on an input data signal having a period 2τ
- and including a plurality of data state transitions, the CDR circuit comprising;
a first delay arrangement for generating a gating signal of duration τ
based on the data state transitions of the input data signal, wherein the first delay arrangement includes a first delay element;a gated voltage-controlled oscillator coupled to the first delay arrangement in such a way that the gating signal enables the gated voltage-controlled oscillator, wherein the gated voltage-controlled oscillator, when enabled, generates the clock signal, wherein the generated clock signal has a duration τ and
is synchronized to the center of the data state transitions of the input data signal,wherein the gated voltage-controlled oscillator includes a first frequency control loop that continually calibrates the frequency of the gated voltage-controlled oscillator to generate the clock signal with the duration τ
, and delays the generated clock signal in such a way that the generated clock signal is synchronized to the center of the data state transitions of the input data signal; anda secondary loop coupled to the first frequency control loop of the gated voltage-controlled oscillator and coupled to the first delay element of the first delay arrangement, wherein the secondary loop includes a frequency detector that tunes the first delay element and tunes the first frequency control loop of the gated voltage-controlled oscillator based on the frequency difference between a recovered clock signal output from the gated voltage-controlled oscillator and an output frequency of a phase locked loop coupled to the frequency detector. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11)
- and including a plurality of data state transitions, the CDR circuit comprising;
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12. A method for recovering a clock signal from a data signal, wherein the data signal has a period 2τ
- and includes a plurality of data state transitions, the method comprising the steps of;
providing the data signal; providing a delay arrangement that delays a version of the data signal and uses the data signal and the delayed version of the data signal to generate a gating signal of duration τ
that corresponds to data state transitions of the data signal;providing a gated voltage-controlled oscillator that is enabled by the gating signal, wherein the gated voltage-controlled oscillator, when enabled, generates the clock signal, wherein the generated clock signal has a duration τ and
is synchronized to the center of the data state transitions of the data signal;calibrating the frequency of the gated voltage-controlled oscillator with a first frequency control loop in such a way the clock signal generated by the gated voltage-controlled oscillator has a duration τ and
is delayed in such a way that the clock signal remains synchronized to the center of the data state transitions of the data signal; andtuning the delay arrangement and the first frequency control loop with a secondary loop coupled between the gated voltage-controlled oscillator and the delay arrangement, wherein the secondary loop includes a frequency detector that tunes the first delay arrangement and tunes the first frequency control loop of the gated voltage-controlled oscillator based on the frequency difference between a recovered clock signal output from the gated voltage-controlled oscillator and an output frequency of a phase locked loop coupled to the frequency detector. - View Dependent Claims (13, 14, 15, 16)
- and includes a plurality of data state transitions, the method comprising the steps of;
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17. An information transmission system, comprising:
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a transmitter for generating a data signal, the data signal having a period 2τ and
including a plurality of data state transitions;a transmission medium having a first end coupled to the transmitter and a second end, the transmission medium transmitting the data signal from the transmitter; and a receiver coupled to the second end of the transmission medium for receiving the data signal generated by the transmitter and transmitted by the transmission medium, the receiver including an integrated circuit having a clock and data recovery circuit, the clock and data recovery circuit generating a recovered clock signal based on the data signal, the clock and data recovery circuit comprising a first delay arrangement for generating a gating signal that has pulses of duration τ
that correspond to data state transitions of the data signal, wherein the first delay arrangement includes a first delay element,a gated voltage-controlled oscillator coupled to the first delay arrangement in such a way that the gating signal enables the gated voltage-controlled oscillator, wherein the gated voltage-controlled oscillator, when enabled, generates the clock signal, wherein the generated clock signal has a duration τ and
is synchronized to the center of the data state transitions of the input data signal,wherein the gated voltage-controlled oscillator includes a first frequency control loop that continually calibrates the frequency of the gated voltage-controlled oscillator to generate the clock signal with the duration τ
, the frequency control loop including a second delay element that delays the generated clock signal by τ
in such a way that the generated clock signal is synchronized to the center of the data state transitions of the input data signal, anda secondary loop coupled to the first frequency control loop of the gated voltage-controlled oscillator and coupled to the first delay element of the first delay arrangement, wherein the secondary loop includes a frequency detector that tunes the first delay element in such a way that the gating signal causes the generated clock signal from the gated voltage-controlled oscillator to remain in the center of the data state transitions of the input data signal and tunes the first frequency control loop of the gated voltage-controlled oscillator in such a way that the frequency of the gated voltage-controlled oscillator matches the frequency of a phase locked loop coupled to the frequency detector, wherein the secondary loop tunes the first delay element and tunes the first frequency control loon of the gated voltage-controlled oscillator based on the frequency difference between a recovered clock signal output from the gated voltage-controlled oscillator and an output frequency of a phase locked loop coupled to the frequency detector. - View Dependent Claims (18, 19, 20, 21)
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Specification