Successive time-to-digital converter for a digital phase-locked loop
First Claim
1. A successive time-to-digital converter (STDC) comprising:
- a frequency detector having an input to accept a reference clock, input to accept a frequency synthesizer clock from a frequency synthesizer, and an output to supply a count of the number of frequency synthesizer clock cycles per reference clock cycle;
a first TDC having an input to accept the reference clock, and input to accept the frequency synthesizer clock, the first TDC measuring a first difference between an edge of a reference clock period and a corresponding edge of a frequency synthesizer clock period, providing the first difference measurement at an output, and providing the frequency synthesizer clock delayed a full cycle;
a phase interpolator having an input to accept the reference clock, an input to accept the frequency synthesizer clock, and an input to accept the first difference measurement, the phase interpolator supplying the reference clock delayed to create a second difference between the edge of the delayed reference clock period and the corresponding edge of the frequency synthesizer clock period, where the second difference is less than the first difference;
a second TDC having an input to accept the delayed reference clock period, and input to accept the delayed frequency synthesizer clock, the second TDC measuring a third difference between the edge of the delayed reference clock period and the corresponding edge of the delayed frequency synthesizer clock period, and providing the third difference measurement as a time duration; and
,a digital signal processor (DSP) having an input to accept the third difference measurement, an input to accept the first difference measurement, an input to accept the count from the frequency detector, and an output to supply a digital error signal to the frequency synthesizer.
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Abstract
A successive time-to-digital converter (STDC) method is provided for supplying a digital word representing the ratio between a phase-locked loop PLL frequency synthesizer signal and a reference clock. The number of frequency synthesizer clock cycles per reference clock cycle is counted. A first difference is measured between a reference clock period and a corresponding frequency synthesizer clock period. In response to the first measurement, a second difference is measured between a delayed reference clock period and the corresponding frequency synthesizer clock period, where the second difference is less than the first difference. A third difference is measured as a time duration between the delayed reference clock period and the corresponding delayed frequency synthesizer clock period. The first and third difference measurements and the count of the number of frequency synthesizer clock cycles per reference clock cycle are used to calculate a digital error signal supplied to the frequency synthesizer.
19 Citations
18 Claims
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1. A successive time-to-digital converter (STDC) comprising:
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a frequency detector having an input to accept a reference clock, input to accept a frequency synthesizer clock from a frequency synthesizer, and an output to supply a count of the number of frequency synthesizer clock cycles per reference clock cycle; a first TDC having an input to accept the reference clock, and input to accept the frequency synthesizer clock, the first TDC measuring a first difference between an edge of a reference clock period and a corresponding edge of a frequency synthesizer clock period, providing the first difference measurement at an output, and providing the frequency synthesizer clock delayed a full cycle; a phase interpolator having an input to accept the reference clock, an input to accept the frequency synthesizer clock, and an input to accept the first difference measurement, the phase interpolator supplying the reference clock delayed to create a second difference between the edge of the delayed reference clock period and the corresponding edge of the frequency synthesizer clock period, where the second difference is less than the first difference; a second TDC having an input to accept the delayed reference clock period, and input to accept the delayed frequency synthesizer clock, the second TDC measuring a third difference between the edge of the delayed reference clock period and the corresponding edge of the delayed frequency synthesizer clock period, and providing the third difference measurement as a time duration; and
,a digital signal processor (DSP) having an input to accept the third difference measurement, an input to accept the first difference measurement, an input to accept the count from the frequency detector, and an output to supply a digital error signal to the frequency synthesizer. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9)
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10. A successive time-to-digital converter (STDC) method for supplying a digital word representing the ratio between a phase-locked loop PLL frequency synthesizer signal and a reference clock, the method comprising:
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accepting a reference clock; accepting a frequency synthesizer signal; counting a number of frequency synthesizer clock cycles per reference clock cycle; measuring a first difference between an edge of a reference clock period and a corresponding edge of a frequency synthesizer clock period; in response to the first measurement, measuring a second difference between an edge of a delayed reference clock period and the corresponding edge of the frequency synthesizer clock period, where the second difference is less than the first difference; measuring a third difference as a time duration between the edge of the delayed reference clock period and the corresponding edge of a frequency synthesizer clock period delayed a full period; using the third difference measurement, the first difference measurement, and the count of the number of frequency synthesizer clock cycles per reference clock cycle, calculating a digital error signal; and
,supplying the digital error signal to a frequency synthesizer. - View Dependent Claims (11, 12, 13, 14, 15, 16, 17, 18)
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Specification