FRACTIONAL-N JITTER ATTENUATOR
First Claim
1. A fractional-N jitter attenuator, comprising:
- (a) a primary loop, including;
(i) a primary counter with an input and an output, wherein the primary counter may include a modulo-K counter;
(ii) a primary register with a first input coupled with the primary counter output and a second input configured for receiving a primary reference clock signal, wherein the primary register is configured to store a primary sampled phase from the primary counter output upon receiving a primary reference clock signal pulse;
(iii) a primary fractional phase predictor with a first input configured for receiving the primary reference clock signal, wherein the primary fractional phase predictor is configured to calculate a primary predicted phase upon receiving a primary reference clock signal pulse, and wherein the primary predicted phase includes an integer number and is based on a rational number primary frequency control word (FCW);
(iv) one of a primary subtractor and a primary adder, configured for calculating an integer number primary difference between the primary predicted phase and the primary sampled phase;
(v) a primary loop filter, configured to receive the primary integer number difference, and to provide a primary loop filtering action to generate a secondary FCW; and
(b) a secondary loop including a fractional-N PLL with a first input configured for receiving a stable reference clock signal, a second input configured for receiving the secondary FCW, and an output configured to provide an output clock signal based on the stable reference clock signal and the secondary FCW, the secondary loop output being coupled with the primary counter input and with a fractional-N jitter attenuator output.
2 Assignments
0 Petitions
Accused Products
Abstract
A phase-locked loop (PLL) has a primary loop (with a reference clock) and a secondary loop (with a stable reference clock). The secondary loop may include a fractional-N PLL, and may include a secondary loop filter, oscillator, output clock counter, and phase predictor using a rational secondary frequency control word (FCW). The primary loop has a register sampling the oscillator phase from the counter, and a phase predictor which uses a primary fractional-N FCW to calculate a predicted phase as an integer number. The primary loop forwards the integer difference between the sampled phase and the predicted phase to a primary loop filter, which outputs the secondary FCW. The primary loop filter has a much lower bandwidth than the secondary loop filter. The PLL may have multiple primary loops, with a hitless switching function. A primary loop may have sleep mode. The PLL may also provide an oscillator sleep function.
9 Citations
22 Claims
-
1. A fractional-N jitter attenuator, comprising:
-
(a) a primary loop, including; (i) a primary counter with an input and an output, wherein the primary counter may include a modulo-K counter; (ii) a primary register with a first input coupled with the primary counter output and a second input configured for receiving a primary reference clock signal, wherein the primary register is configured to store a primary sampled phase from the primary counter output upon receiving a primary reference clock signal pulse; (iii) a primary fractional phase predictor with a first input configured for receiving the primary reference clock signal, wherein the primary fractional phase predictor is configured to calculate a primary predicted phase upon receiving a primary reference clock signal pulse, and wherein the primary predicted phase includes an integer number and is based on a rational number primary frequency control word (FCW); (iv) one of a primary subtractor and a primary adder, configured for calculating an integer number primary difference between the primary predicted phase and the primary sampled phase; (v) a primary loop filter, configured to receive the primary integer number difference, and to provide a primary loop filtering action to generate a secondary FCW; and (b) a secondary loop including a fractional-N PLL with a first input configured for receiving a stable reference clock signal, a second input configured for receiving the secondary FCW, and an output configured to provide an output clock signal based on the stable reference clock signal and the secondary FCW, the secondary loop output being coupled with the primary counter input and with a fractional-N jitter attenuator output. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15)
-
-
16. A method for jitter attenuation, comprising the following steps:
-
(a) in a primary PLL loop, based on a primary reference clock signal and a rational first frequency control word (FCW), calculating an integer primary predicted phase;
based on the primary reference clock signal and a secondary PLL loop output clock signal, sampling a phase at a counter output to obtain an integer primary sampled phase, wherein the counter may include a modulo-K counter;
calculating a primary difference by subtracting the primary sampled phase from the primary predicted phase;(b) loop filtering the primary difference in a primary loop filter to obtain a rational second FCW; (c) forwarding the second FCW to a secondary loop; (d) based on the second FCW and a secondary reference clock signal, calculating a secondary predicted phase;
based on the secondary reference clock signal and the secondary PLL loop output clock signal, sampling a phase to obtain a secondary sampled phase;
calculating a secondary difference by subtracting the secondary sampled phase from the secondary predicted phase; and(e) loop filtering the secondary difference in a secondary loop filter to obtain an oscillator control code to control a controlled oscillator and to determine a frequency of the secondary PLL loop output clock signal.
-
-
17. A programmable jitter attenuator, comprising:
-
a fractional-N PLL with a stable reference signal input and a frequency control word (FCW) input, configured to produce an output clock signal at a PLL output; a counter with an input coupled with the PLL output, wherein the counter may include a modulo-K counter; a programmable processor with a first input coupled with a counter output, a second input configured for receiving a primary reference clock signal, and an output coupled with the fractional-N PLL FCW input to provide a secondary FCW; a memory coupled with the programmable processor and configured to store at least one of program instructions or data; wherein the programmable processor is programmed to execute instructions for the following operations; (a) in the programmable processor, based on the primary reference clock signal and a rational primary FCW, calculating an integer primary predicted phase;
based on the primary reference clock signal and the fractional-N PLL output clock signal, sampling a phase at the counter output to obtain an integer primary sampled phase;
calculating a primary difference by subtracting the primary sampled phase from the primary predicted phase;(b) loop filtering the primary difference in a primary loop filter to obtain the secondary FCW; and (c) forwarding the secondary FCW to the fractional-N PLL to control the fractional-N PLL and to determine a frequency of the fractional-N PLL output clock signal.
-
-
18. A tangible non-transitory memory, carrying software instructions for the following operations:
-
(a) in a programmable processor, based on a primary reference clock signal and a rational primary FCW, calculating an integer primary predicted phase;
based on the primary reference clock signal and a fractional-N PLL output clock signal, sampling a phase at a counter output to obtain an integer primary sampled phase, wherein the counter may include a modulo-K counter;
calculating a primary difference by subtracting the primary sampled phase from the primary predicted phase;(b) loop filtering the primary difference in a primary loop filter to obtain a rational secondary FCW; and (c) forwarding the secondary FCW to the fractional-N PLL to control the fractional-N PLL and to determine a frequency of the fractional-N PLL output clock signal.
-
-
19. A programmable jitter attenuator, comprising:
-
a controlled oscillator with an oscillator control code (OCC) input, and an output configured to produce an output clock signal; a counter with an input coupled with the controlled oscillator output, wherein the counter may include a modulo-K counter; a programmable processor with a first input coupled with a counter output, a second input configured for receiving a primary reference clock signal, a third input configured for receiving a secondary reference signal, and an output coupled with the controlled oscillator input to provide an OCC; a tangible non-transitory memory coupled with the programmable processor and configured to store at least one of program instructions or data; wherein the programmable processor is programmed to execute instructions for the following operations; (a) based on a primary reference clock signal and a rational primary frequency control word (FCW), calculating an integer primary predicted phase;
based on the primary reference clock signal and the output clock signal, sampling a phase at the counter output to obtain an integer primary sampled phase;
calculating a primary difference by subtracting the primary sampled phase from the primary predicted phase;(b) loop filtering the primary difference in a primary loop filter to obtain a secondary FCW; (c) based on the secondary FCW and the secondary reference clock signal, calculating a secondary predicted phase;
based on the secondary reference clock signal and the output clock signal, sampling a phase to obtain a secondary sampled phase;
calculating a secondary difference by subtracting the secondary sampled phase from the secondary predicted phase;(d) loop filtering the secondary difference in a secondary loop filter to obtain the OCC to control a frequency of the output clock signal; and (e) forwarding the OCC to the OCC input. - View Dependent Claims (20, 21)
-
-
22. A tangible non-transitory memory, carrying software instructions for the following operations:
-
(a) in a programmable processor, based on a primary reference clock signal and a rational primary frequency control word (FCW), calculating an integer primary predicted phase;
based on a primary reference clock signal and a controlled oscillator output clock signal, sampling a phase at a counter output to obtain an integer primary sampled phase, wherein the counter may include a modulo-K counter;
calculating a primary difference by subtracting the primary sampled phase from the primary predicted phase;(b) filtering the primary difference in a primary loop filter to obtain a secondary FCW; (c) based on the secondary FCW and a secondary reference clock signal, calculating a secondary predicted phase;
based on the secondary reference clock signal and the output clock signal, sampling a phase to obtain a secondary sampled phase;
calculating a secondary difference by subtracting the secondary sampled phase from the secondary predicted phase;(d) filtering the secondary difference in a secondary loop filter to obtain an oscillator control code (OCC) to control a frequency of the output clock signal; and (e) forwarding the OCC to a controlled oscillator input.
-
Specification