Digital Clock Generation and Variation Control Circuitry

Abstract

In certain aspects, a digital circuit comprises a delay line to generate a plurality of delayed versions of an input clock. The digital circuit also comprises selection circuitry to provide a selected one of the plurality of delayed versions of the input clock based on a clock selection signal and feedback circuitry to generate the clock selection signal based on the selected one of the plurality of delayed versions of the input clock and based on the input clock. The clock selection signal is further used for selecting and generating other clocks and/or for variation control.

What is claimed is: 
     
         1 . A digital circuit, comprising:
 a first delay line configured to receive an input clock, the first delay line comprising a plurality of first delay units coupled in series, each of the plurality of first delay units being configured to provide substantially a same first delay, and the plurality of first delay units being configured to provide a plurality of delayed versions of the input clock with each of the plurality of first delay units being configured to provide a respective one of the plurality of delayed versions of the input clock;   first selection circuitry configured to receive a first set of the plurality of delayed versions of the input clock and to provide first selected one of the plurality of delayed versions of the input clock based on a clock selection signal; and   feedback circuitry configured to generate the clock selection signal based on the first selected one of the plurality of delayed versions of the input clock and based on the input clock.   
     
     
         2 . The digital circuit of  claim 1 , wherein the first selected one of the plurality of delayed versions of the input clock is offset in time from the input clock by a fraction of one clock period of the input clock. 
     
     
         3 . The digital circuit of  claim 1 , wherein the feedback circuitry comprises a digital counter configured to generate the clock selection signal in response to the input clock and a count control signal. 
     
     
         4 . The digital circuit of  claim 3 , wherein the feedback circuitry further comprises a first register configured to provide the count control signal in response to the input clock and the first selected one of the plurality of delayed versions of the input clock. 
     
     
         5 . The digital circuit of  claim 3 , wherein the count control signal is the first selected one of the plurality of delayed versions of the input clock. 
     
     
         6 . The digital circuit of  claim 1 , wherein the clock selection signal comprises multi-bit encoded data and the feedback circuitry is configured to change the multi-bit encoded data in response to a rising or a falling edge of the input clock and the first selected one of the plurality of delayed versions of the input clock. 
     
     
         7 . The digital circuit of  claim 1  further comprising second selection circuitry configured to receive a second set of the plurality of delayed versions of the input clock and to provide second selected one or more of the plurality of delayed versions of the input clock based on the clock selection signal. 
     
     
         8 . The digital circuit of  claim 7 , wherein at least one of the second selected one or more of the plurality of delayed versions of the input clock is offset in time from the input clock by a fraction of one clock period of the input clock. 
     
     
         9 . The digital circuit of  claim 7  further comprising clock multiplier circuitry configured to receive the input clock and at least one of the second selected one or more of the plurality of delayed versions of the input clock and to provide a first output clock with a frequency that is a first integer multiple of a frequency of the input clock. 
     
     
         10 . The digital circuit of  claim 9 , wherein the clock multiplier circuitry comprises one or more XOR gates. 
     
     
         11 . The digital circuit of  claim 9 , wherein the clock multiplier circuitry comprises frequency divider circuitry configured to receive the input clock and at least one of the second selected one or more of the plurality of delayed versions of the input clock and to provide one or more divided clocks having frequencies that are about one-half of respective frequencies of the input clock and at least one of the second selected one or more of the plurality of delayed versions of the input clock. 
     
     
         12 . The digital circuit of  claim 9  further comprising:
 a second delay line configured to receive the first output clock, the second delay line comprising a plurality of second delay units coupled in series, each of the plurality of second delay units being configured to provide substantially a same second delay, and the plurality of second delay units being configured to provide a plurality of delayed versions of the first output clock with each of the plurality of second delay units being configured to provide a respective one of the plurality of delayed versions of the first output clock; 
 third selection circuitry configured to receive a set of the plurality of delayed versions of the first output clock and to provide a selected one or more of the plurality of delayed versions of the first output clock based on the clock selection signal; 
 second clock multiplier circuitry configured to receive the first output clock and at least one of the selected one or more of the plurality of delayed versions of the first output clock and to provide a second output clock having a frequency that is a second integer multiple of a frequency of the first output clock. 
 
     
     
         13 . The digital circuit of  claim 1  further comprising variation control circuitry configured to adjust a supply voltage or an operation clock frequency or both based on the clock selection signal. 
     
     
         14 . A method for clock generation, comprising:
 receiving an input clock;   generating a plurality of delayed versions of the input clock using a first delay line, the first delay line comprising a plurality of first delay units coupled in series, each of the plurality of first delay units being configured to provide substantially a same first delay, and the plurality of first delay units being configured to provide a plurality of delayed versions of the input clock with each of the plurality of first delay units being configured to provide a respective one of the plurality of delayed versions of the input clock;   selecting first selected one of the plurality of delayed versions of the input clock out of a first set of the plurality of delayed versions of the input clock based on a clock selection signal; and   generating the clock selection signal based on the first selected one of the plurality of delayed versions of the input clock and based on the input clock.   
     
     
         15 . The method of  claim 14 , wherein the first selected one of the plurality of delayed versions of the input clock is offset in time from the input clock by a fraction of one clock period of the input clock. 
     
     
         16 . The method of  claim 14 , wherein generating the clock selection signal comprises changing a digital count data in response to the input clock and a count control signal. 
     
     
         17 . The method of  claim 16 , wherein the clock selection signal comprises multi-bit encoded data, and wherein changing the digital count data comprises changing the multi-bit encoded data in response to a rising or a falling edge of the input clock and the first selected one of the plurality of delayed versions of the input clock. 
     
     
         18 . The method of  claim 14  further comprising selecting second selected one or more of the plurality of delayed versions of the input clock out of a second set of the plurality of delayed versions of the input clock based on the clock selection signal. 
     
     
         19 . The method of  claim 18  further comprising:
 receiving the input clock and at least one of the second selected one or more of the plurality of delayed versions of the input clock; and 
 providing a first output clock having a frequency that is a first integer multiple of a frequency of the input clock. 
 
     
     
         20 . The method of  claim 19 , wherein providing the first output clock comprises generating one or more divided clocks having frequencies that are about one-half of respective frequencies of the input clock and at least one of the second selected one or more of the plurality of delayed versions of the input clock. 
     
     
         21 . The method of  claim 19  further comprising:
 generating a plurality of delayed versions of the first output clock using a second delay line, the second delay line comprising a plurality of second delay units coupled in series, each of the plurality of second delay units being configured to provide substantially a same second delay, and the plurality of second delay units being configured to provide a plurality of delayed versions of the first output clock with each of the plurality of second delay units being configured to provide a respective one of the plurality of delayed versions of the first output clock; 
 selecting a selected one or more of the plurality of delayed versions of the first output clock out of a set of the plurality of delayed versions of the first output clock based on the clock selection signal; and 
 providing a second output clock having a frequency that is a second integer multiple of a frequency of the input clock using the first output clock and at least one of the selected one or more of the plurality of delayed versions of the first output clock. 
 
     
     
         22 . The method of  claim 14  further comprising adjusting a supply voltage or an operation clock frequency or both based on the clock selection signal. 
     
     
         23 . A digital circuit, comprising:
 a first delay line configured to receive an input clock, the first delay line comprising a plurality of first delay units coupled in series, each of the plurality of first delay units being configured to provide substantially a same first delay, and the plurality of first delay units being configured to provide a plurality of delayed versions of the input clock with each of the plurality of first delay units being configured to provide a respective one of the plurality of delayed versions of the input clock;   means for selecting first selected one of the plurality of delayed versions of the input clock out of a first set of the plurality of delayed versions of the input clock based on a clock selection signal; and   means for generating the clock selection signal based on the first selected one of the plurality of delayed versions of the input clock and based on the input clock.   
     
     
         24 . The digital circuit of  claim 23 , wherein the first selected one of the plurality of delayed versions of the input clock is offset in time from the input clock by a fraction of one clock period of the input clock. 
     
     
         25 . The digital circuit of  claim 23 , wherein the means for generating the clock selection signal comprises means for changing a digital count data in response to the input clock and a count control signal, and wherein the means for generating the clock selection signal further comprises means for generating the count control signal in response to the input clock and the first selected one of the plurality of delayed versions of the input clock. 
     
     
         26 . The digital circuit of  claim 23 , further comprising means for selecting second selected one or more of the plurality of delayed versions of the input clock out of a second set of the plurality of delayed versions of the input clock based on the clock selection signal. 
     
     
         27 . The digital circuit of  claim 26 , wherein at least one of the second selected one or more of the plurality of delayed versions of the input clock is offset in time from the input clock by a fraction of one clock period of the input clock. 
     
     
         28 . The digital circuit of  claim 26  further comprising means for providing a first output clock having a frequency that is a first integer multiple of a frequency of the input clock. 
     
     
         29 . The digital circuit of  claim 28  further comprising:
 a second delay line configured to receive the first output clock, the second delay line comprising a plurality of second delay units coupled in series, each of the plurality of second delay units being configured to provide substantially a same second delay, and the plurality of second delay units being configured to provide a plurality of delayed versions of the first output clock with each of the plurality of second delay units being configured to provide a respective one of the plurality of delayed versions of the first output clock; 
 means for selecting a selected one or more of the plurality of delayed versions of the first output clock out of a set of the plurality of delayed versions of the first output clock based on the clock selection signal; and 
 means for providing a second output clock having a frequency that is a second integer multiple of a frequency of the input clock using the first output clock and at least one of the selected one or more of the plurality of delayed versions of the first output clock. 
 
     
     
         30 . The digital circuit of  claim 23  further comprising means for adjusting a supply voltage or an operation clock frequency or both based on the clock selection signal.