AUTOMATIC PHASE-DETECTION CIRCUIT FOR CLOCKS WITH KNOWN RATIOS
First Claim
Patent Images
1. An automatic phase detection circuit for clocks, comprising:
- a sequential state element having a data input, a first clock input and a data output;
a first clock operably coupled to the data input;
a second clock operably coupled to the first clock input;
a serial input, parallel output shift register having a second clock input operably coupled to the second clock and the serial input operably coupled to the data output;
a signature register configured to store a repetitive portion of an output sequence of the data output;
a comparator operably coupled to the parallel output of the shift register and operably coupled to the signature register, the comparator configured to compare a content of the signature register and a content of the shift register; and
wherein the comparator generates a pulse when the content of the signature register and the content of the shift register match.
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Abstract
An automatic phase detection circuit for generating an internal synchronization signal when two clock input signals achieve a certain phase relationship. No external reference signal is required. The logic state of one clock is sampled on the active edge of the other clock and stored in a shift register. The content of the shift register is compared to a pre-defined signature and a sync signal is generated when the content matches the pre-defined signature. A mask register may be used to define which bits of the shift register and pre-defined signature are compared.
16 Citations
22 Claims
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1. An automatic phase detection circuit for clocks, comprising:
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a sequential state element having a data input, a first clock input and a data output; a first clock operably coupled to the data input; a second clock operably coupled to the first clock input; a serial input, parallel output shift register having a second clock input operably coupled to the second clock and the serial input operably coupled to the data output; a signature register configured to store a repetitive portion of an output sequence of the data output; a comparator operably coupled to the parallel output of the shift register and operably coupled to the signature register, the comparator configured to compare a content of the signature register and a content of the shift register; and wherein the comparator generates a pulse when the content of the signature register and the content of the shift register match. - View Dependent Claims (2, 3, 4, 5, 6, 7)
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8. A method of performing automatic phase detection for clocks with a certain frequency ratio, the method comprising:
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receiving a first clock signal and a second clock signal; identifying a repetitive sequence that occurs when an active edge of the first clock signal is used to sample a logic state of the second clock signal; sampling the second clock signal on each active edge of the first clock signal to obtain a sample sequence; and generating a sync pulse when the sample sequence matches the repetitive sequence. - View Dependent Claims (9, 10, 11, 12, 13, 14)
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15. A programmable clock module having a first clock input and a second clock input, comprising:
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a sequential state element having a data input operably coupled to the first clock input, a data output and a clock input operably coupled to the second clock input; a serial input port, parallel output port n-bit shift register having a clock input port, the clock input port operably coupled to the second clock input and the serial input port operably coupled to the data output; an n-bit comparator operably coupled to the shift register and configured to compare a content of the shift register with a pre-defined signature; an n-bit mask register operably coupled to the comparator and configured to mask a portion of the comparison; and wherein the comparator generates a pulse when the content of the shift register matches the pre-defined signature. - View Dependent Claims (16, 17, 18, 19, 20, 21, 22)
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Specification