Methods and Systems for Locally Generating Non-Integral Divided Clocks with Centralized State Machines

Abstract

A method for locally generating a ratio clock on a chip includes generating a global clock signal having a global clock cycle. A centralized state machine includes a counter going through a complete cycle in response to a non-integer number of global clock cycles, the state machine generating a control signal in response to the counter. The control signal is provided to staging latches, the staging latches generating a clock high signal and a clock low signal. Local pass gates generate an (n+0.5)-to-1 clock signal in response to the global clock signal, the clock high signal and the clock low signal.

1 . Circuitry for locally generating a ratio clock on a chip, comprising:
 circuitry for generating a global clock signal having a global clock cycle;   a centralized state machine including a counter going through a complete cycle in response to a non-integer number of global clock cycles, the state machine generating a control signal in response to the counter;   staging latches receiving the control signal and generating a clock high signal and a clock low signal;   a local pass gate receiving the clock low signal and the clock high signal and generating an (n+0.5)-to-1 clock signal in response to the global clock signal, the clock high signal and the clock low signal.   
   
   
       2 . The circuitry of  claim 1  wherein the state machine is partially centralized. 
   
   
       3 . The circuitry of  claim 1  wherein the clock high signal and clock low signal having patterns derived from a waveform of a target divided ratio clock, the clock high signal and clock low signal having patterns that match the targeted divided clock frequency and duty cycle 
   
   
       4 . The circuitry of  claim 1  further comprising combination logic positioned between pairs of staging latches. 
   
   
       5 . The circuitry of  claim 4  wherein the combination logic is a delay. 
   
   
       6 . The circuitry of  claim 1  further comprising group combination logic for receiving delayed control signals from the staging latches, the group combination logic generating the clock low signal and clock high signal. 
   
   
       7 . The circuitry of  claim 1  wherein the state machine includes multiple state machines, each of which generates different control signal patterns. 
   
   
       8 . The circuitry of  claim 7  further comprising a multiplexer for selecting between the different control signal patterns. 
   
   
       9 . The circuitry of  claim 1  wherein equal delays are maintained between the state machine and local clock generation circuits including the pass-gates. 
   
   
       10 . The circuitry of  claim 4  wherein the pair of latches are clocked by alternate clock phases. 
   
   
       11 . The circuitry of  claim 1  wherein a first staging latch is used to synchronize timing. 
   
   
       12 . The circuitry of  claim 1  wherein the staging latches include 4 staging latches, one staging latch directly generating the clock low signal and another staging latch directly generating the clock high signal for generating a 1.5-to-1 ratio clock. 
   
   
       13 . The circuitry of  claim 12  further comprising a delay positioned between a first staging latch and a second staging latch, a delay position between the second staging latch and a third staging latch and a delay positioned between the third staging latch and the fourth staging latch, the first and third staging latches being clocked by a first phase of the global clock, the second and fourth staging latches being clocked by a second phase of the global clock signal, the second phase being opposite the first phase, the first staging latch generating the clock low signal and the fourth staging latch generating the clock high signal for generating a 1.5-to-1 ratio clock. 
   
   
       14 . The circuitry of  claim 6  wherein the staging latches include 3 staging latches and the group combination logic includes a NAND gate. 
   
   
       15 . The circuitry of  claim 14  further comprising a delay positioned between a first staging latch and a second staging latch and a delay position between the second staging latch and a third staging latch, the output of the first staging latch and the third staging latch being applied to the NAND gate to generate the clock low signal, the output of the second staging latch defining the clock high signal. 
   
   
       16 . The circuitry of  claim 6  wherein the staging latches include 2 latches and the group combination logic is an inverter. 
   
   
       17 . The circuitry of  claim 16  further comprising a delay position between a first staging latch and a second staging latch, the output of the first staging latch defining the clock low signal and the output of the second staging latch being applied to the inverter to generate the clock high signal.