Delay-lock loop and method adapting itself to operate over a wide frequency range
First Claim
1. A system for providing at least one periodic output clock signal, comprising:
- a programmable frequency divider having an input terminal receiving an input clock signal, a control terminal receiving a divider select signal, and an output terminal, the programmable frequency being operable to divide the frequency of the input clock signal by an integer number determined by the select signal to generate a clock signal at the output terminal;
a delay-lock loop having phase detector and a delay line, the delay line of the delay-lock loop having an input terminal coupled to the output terminal of the programmable frequency divider so that the clock signal generated by the programmable frequency divider propagates through the delay line to generate the at least one periodic output clock signal; and
an initialization circuit coupled to the programmable frequency divider and the delay-lock loop, the initialization circuit being operative during an initialization period to set the delay of the delay line to a minimum delay value and to compare the timing of the at least one periodic output clock signal to the timing of the input clock signal, the initialization circuit generating the select signal with a value determined by the timing comparison.
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Accused Products
Abstract
A delay-lock loop receives an input clock signal from the output of a programmable divider that receives a reference clock signal. The delay-lock loop includes a voltage-controlled delay line generating a plurality of delayed clock signals having different phases. A plurality of the delayed clock signals are combined to generate a plurality of output signals. During an initialization period, an initialization circuit sets the delay of the delay line to a minimum delay value and then compares this delay value to the period of the input clock signal. Based on this comparison, the initialization circuit programs the programmable divider and adjusts the number of delayed clock signals combined to generate the output signals. More specifically, as the frequency of the reference clock signal increases, the divider is programmed to divide by a greater number, and a larger number of delay clock signals are combined to generate the output signals.
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Citations
38 Claims
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1. A system for providing at least one periodic output clock signal, comprising:
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a programmable frequency divider having an input terminal receiving an input clock signal, a control terminal receiving a divider select signal, and an output terminal, the programmable frequency being operable to divide the frequency of the input clock signal by an integer number determined by the select signal to generate a clock signal at the output terminal; a delay-lock loop having phase detector and a delay line, the delay line of the delay-lock loop having an input terminal coupled to the output terminal of the programmable frequency divider so that the clock signal generated by the programmable frequency divider propagates through the delay line to generate the at least one periodic output clock signal; and an initialization circuit coupled to the programmable frequency divider and the delay-lock loop, the initialization circuit being operative during an initialization period to set the delay of the delay line to a minimum delay value and to compare the timing of the at least one periodic output clock signal to the timing of the input clock signal, the initialization circuit generating the select signal with a value determined by the timing comparison. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12)
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13. A memory device, comprising:
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a row address circuit operable to receive and decode row address signals applied to external address terminals of the memory device; a column address circuit operable to receive and decode column address signals applied to the external address terminals; a memory cell array operable to store data written to and read from the array at a location determined by the decoded row address signals and the decoded column address signals; a read data path circuit operable to couple read data signals from the memory cell array to external data terminals of the memory device, the read data signals being applied to the external data terminals responsive to a read data strobe signal; a write data path circuit operable to couple write data signals from the external data terminals of the memory device responsive to a write data strobe signal, the write data signals being coupled to the memory cell array; a command decoder operable to decode a plurality of command signals applied to respective external command terminals of the memory device, the command decoder being operable to generate control signals corresponding to the decoded command signals; a strobe generating circuit operable to generate either the write data strobe signal or the read data strobe signal from an internal clock signal, the strobe generating circuit comprising; a programmable frequency divider having an input terminal receiving a reference clock signal, a control terminal receiving a divider select signal, and an output terminal, the programmable frequency divider being operable to divide the frequency of the reference clock signal by an integer number determined by the select signal to generate a clock signal at the output terminal; a delay-lock loop having phase detector and a delay line, the delay line of the delay-lock loop having an input terminal coupled to the output terminal of the programmable frequency divider so that the clock signal generated by the programmable frequency divider propagates through the delay line to generate the at least one periodic output clock signal from which either the write data strobe signal or the read data strobe signal is derived; and an initialization circuit coupled to the programmable frequency divider and the delay-lock loop, the initialization circuit being operative during an initialization period to set the delay of the delay line to a minimum delay value and to compare the timing of the at least one periodic output clock signal to the timing of the reference clock signal, the initialization circuit generating the select signal with a value determined by the timing comparison. - View Dependent Claims (14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25)
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26. A processor-based system, comprising
a processor having a processor bus; -
an input device coupled to the processor through the processor bus adapted to allow data to be entered into the computer system; an output device coupled to the processor through the processor bus adapted to allow data to be output from the computer system; and a memory device coupled to the processor bus adapted to allow data to be stored, the memory device comprising; a row address circuit operable to receive and decode row address signals applied to external address terminals of the memory device; a column address circuit operable to receive and decode column address signals applied to the external address terminals; a memory cell array operable to store data written to and read from the array at a location determined by the decoded row address signals and the decoded column address signals; a read data path circuit operable to couple read data signals from the memory cell array to external data terminals of the memory device, the read data signals being applied to the external data terminals responsive to a read data strobe signal; a write data path circuit operable to couple write data signals from the external data terminals of the memory device responsive to a write data strobe signal, the write data signals being coupled to the memory cell array; a command decoder operable to decode a plurality of command signals applied to respective external command terminals of the memory device, the command decoder being operable to generate control signals corresponding to the decoded command signals; a strobe generating circuit operable to generate either the write data strobe signal or the read data strobe signal from an internal clock signal, the strobe generating circuit comprising; a programmable frequency divider having an input terminal receiving a reference clock signal, a control terminal receiving a select signal, and an output terminal, the programmable frequency divider being operable to divide the frequency of the reference clock signal by an integer number determined by the select signal to generate a clock signal at the output terminal; a delay-lock loop having phase detector and a delay line, the delay line of the delay-lock loop having an input terminal coupled to the output terminal of the programmable frequency divider so that the clock signal generated by the programmable frequency divider propagates through the delay line to generate the at least one periodic output clock signal from which either the write data strobe signal or the read data strobe signal is derived; and an initialization circuit coupled to the programmable frequency divider and the delay-lock loop, the initialization circuit being operative during an initialization period to set the delay of the delay line to a minimum delay value and to compare the timing of the at least one periodic output clock signal to the timing of the reference clock signal, the initialization circuit generating the select signal with a value determined by the timing comparison. - View Dependent Claims (27, 28, 29, 30, 31, 32, 33, 34, 35, 36, 37, 38)
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Specification