Digital Phase Lock System with Dithering Pulse-Width-Modulation Controller
First Claim
1. A Digital Phase-Locked Loop (DPLL) comprising:
- a reference clock input receiving a reference clock having a reference frequency;
a digitally-controlled oscillator (DCO) that generates an output clock having an output frequency that is determined by a digital oscillator input, the digital oscillator input having most-significant-bits (MSBs) and a least-significant-bit (LSB);
a feedback divider that divides the output clock by M to generate a feedback clock, wherein the output frequency is M times the reference frequency when the feedback clock is phase locked to the reference clock, wherein M is a whole number;
a control divider that divides the output clock by C to generate a control clock, wherein the output frequency is C times a control frequency of the control clock, and wherein the control frequency is C/M times the reference frequency when the feedback clock is phase locked to the reference clock, wherein C and M/C are each whole numbers;
a Time-to-Digital Converter (TDC) that receives the reference clock and the feedback clock, the TDC performing phase comparisons of the feedback clock to the reference clock using a coarse time resolution to generate a coarse phase compare signal and using a fine time resolution to generate a fine phase compare signal, wherein the fine time resolution represents a smaller amount of time than the coarse time resolution;
a coarse digital loop filter that receives the coarse time resolution from the TDC and generates the MSBs to the DCO;
a fine digital loop filter that receives the fine time resolution from the TDC and generates a fine loop filter value; and
a Pulse-Width-Modulation (PWM) controller that generates M/C LSB bits for each period of the reference clock, the M/C LSB bits forming a pulse that has a pulse-width determined by the fine loop filter value from the fine digital loop filter, the PWM controller delivering one of the M/C LSB bits to the digital oscillator input of the DCO in response to each period of the control clock,whereby the PWM controller generates LSB'"'"'s to the digitally-controlled oscillator by modulating the pulse-width in response to the fine loop filter value.
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Abstract
A Digital Phase-Locked Loop (DPLL) has a digitally-controlled oscillator (DCO) that generates an output clock frequency determined by a digital input with most-significant-bits (MSB'"'"'s) and a least-significant-bit (LSB). The LSB is generated by a Pulse-Width-Modulation (PWM) controller clocked by a control clock that is the output clock divided by C. A reference clock is compared to a feedback clock that is the output clock divided by M. The PWM controller generates M/C LSB'"'"'s for each reference clock period and loads them in parallel to a parallel-to-serial shift register that serially delivers the LSBs. The pulse width is determined by a fine digital loop filter that filters phase comparison results using a fine time resolution. A coarse digital loop filter generates the MSB'"'"'s from phase comparison results using a coarse time resolution. LSB waveforms are dithered by randomly selecting high-going or low-going pulses and randomly adjusting pulse widths.
38 Citations
20 Claims
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1. A Digital Phase-Locked Loop (DPLL) comprising:
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a reference clock input receiving a reference clock having a reference frequency; a digitally-controlled oscillator (DCO) that generates an output clock having an output frequency that is determined by a digital oscillator input, the digital oscillator input having most-significant-bits (MSBs) and a least-significant-bit (LSB); a feedback divider that divides the output clock by M to generate a feedback clock, wherein the output frequency is M times the reference frequency when the feedback clock is phase locked to the reference clock, wherein M is a whole number; a control divider that divides the output clock by C to generate a control clock, wherein the output frequency is C times a control frequency of the control clock, and wherein the control frequency is C/M times the reference frequency when the feedback clock is phase locked to the reference clock, wherein C and M/C are each whole numbers; a Time-to-Digital Converter (TDC) that receives the reference clock and the feedback clock, the TDC performing phase comparisons of the feedback clock to the reference clock using a coarse time resolution to generate a coarse phase compare signal and using a fine time resolution to generate a fine phase compare signal, wherein the fine time resolution represents a smaller amount of time than the coarse time resolution; a coarse digital loop filter that receives the coarse time resolution from the TDC and generates the MSBs to the DCO; a fine digital loop filter that receives the fine time resolution from the TDC and generates a fine loop filter value; and a Pulse-Width-Modulation (PWM) controller that generates M/C LSB bits for each period of the reference clock, the M/C LSB bits forming a pulse that has a pulse-width determined by the fine loop filter value from the fine digital loop filter, the PWM controller delivering one of the M/C LSB bits to the digital oscillator input of the DCO in response to each period of the control clock, whereby the PWM controller generates LSB'"'"'s to the digitally-controlled oscillator by modulating the pulse-width in response to the fine loop filter value. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9)
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10. A digital phase-locked system comprising:
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a digital phase comparator that receives a reference clock and a feedback clock and generates a coarse phase comparison result and a fine phase comparison result; a coarse digital loop filter that digitally filters the coarse phase comparison result to generate most-significant-bits (MSBs); a fine digital loop filter that digitally filters the fine phase comparison result to generate a fine filter value; a Pulse-Width-Modulation (PWM) controller that generates a pattern of least-significant-bits (LSBs) that represent a pulse having a pulse-width determined by the fine filter value; a parallel-to-serial shift register that is loaded in parallel by the PWM controller with the pattern of LSB'"'"'s; a digitally-controlled oscillator (DCO) that has a digital input that receives the MSBs and the LSBs and generates an output clock; a feedback divider that receives the output clock and generates the feedback clock; and a control divider that receives the output clock and generates a control clock; wherein the parallel-to-serial shift register shifts the pattern of LSBs to the digital input of the DCO, wherein the pattern of LSBs are serially delivered to the digital input in response to the control clock; whereby the pulse-width of the pattern of LSBs is modulated in response to the fine filter value. - View Dependent Claims (11, 12, 13, 14, 15, 16)
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17. A low-phase-noise Digital Phase-Locked Loop comprising:
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a reference clock input receiving a reference clock having a reference frequency; digitally-controlled oscillator (DCO) means for generating an output clock having an output frequency that is determined by a digital oscillator input, the digital oscillator input having most-significant-bits (MSBs) and a least-significant-bit (LSB); feedback divider means for dividing the output clock by M to generate a feedback clock, wherein the output frequency is M times the reference frequency when the feedback clock is phase locked to the reference clock, wherein M is a whole number; control divider means for dividing the output clock by C to generate a control clock, wherein the output frequency is C times a control frequency of the control clock, and wherein the control frequency is C/M times the reference frequency when the feedback clock is phase locked to the reference clock, wherein C and M/C are each whole numbers; Time-to-Digital Converter (TDC) means, receiving the reference clock and the feedback clock, for coarsely comparing phases of the feedback clock to the reference clock using a coarse time resolution to generate a coarse phase compare signal, and for finely comparing phases of the feedback clock to the reference clock using a fine time resolution to generate a fine phase compare signal, wherein the fine time resolution represents a smaller amount of time than the coarse time resolution; coarse digital loop filter means for digitally filtering the coarse time resolution from the TDC means to generate the MSBs to the DCO means; fine digital loop filter means for digitally filtering the fine time resolution from the TDC means to generate a fine loop filter value; and Pulse-Width-Modulation (PWM) controller means for generating M/C LSB bits for each period of the reference clock, the M/C LSB bits forming a pulse that has a pulse-width determined by the fine loop filter value from the fine digital loop filter means, the PWM controller means also for delivering one of the M/C LSB bits to the digital oscillator input of the DCO means in response to each period of the control clock, whereby the PWM controller means generates LSB'"'"'s to the DCO means by modulating the pulse-width in response to the fine loop filter value. - View Dependent Claims (18, 19, 20)
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Specification