Digital controlled oscillator based clock generator for multi-channel design
A clock divider includes, in part, a pair of counters and a programmable delay line. A first one of the counters operates at a first frequency and is configured to count using a first integer portion of the divisor. The second counter operates at a second frequency smaller than the first frequency and is configured to count using a second integer portion of the divisor. The programmable delay line includes, in part, a chain of delay elements configured to generate a multitude of delays of the output of the second counter. A multiplexer selects one of the generated delays in accordance with the fractional portion of the divisor. The second counter increases its count only when the first counter reaches a terminal count. The first and second integer portions are loaded respectively into the first and second counters when the second counter reaches its terminal count.
1. A clock divider configured to divide a frequency of a received clock signal by a number having an integer portion and a fractional portion, the clock divider comprising:
a first counter configured to generate a first output signal at a first frequency, where the first frequency is based on the received clock signal and a first portion of the integer portion of the number;
a second counter configured to receive the first output signal and the received clock signal to generate a second output signal at a second frequency, where the second frequency is based on the received clock signal and a second portion of the integer portion of the number, and where the second frequency is smaller than the first frequency; and
a programmable delay line comprising a chain of delay elements and adapted to delay the second output signal based on the fractional portion of the number.
2. The clock divider of claim 1 wherein the first counter is a down counter.
3. The clock divider of claim 2 wherein the second counter is an up counter.
4. The clock divider of claim 3 wherein the first counter is a roll counter.
5. The clock divider of claim 3 wherein said second counter is enabled to increase its count only when the first counter reaches a terminal count.
6. The clock divider of claim 5 further comprising a flip-flop that is enabled to store an inverse of its output value when the first counter reaches a count of 1 and the second counter reaches its terminal count.
7. The clock divider of claim 6 wherein said first portion of the integer portion of the number is loaded into the first counter and said second portion of the integer portion of the number is loaded into the second counter whenever the first counter reaches the count of 1 and the second counter reaches its terminal count.
8. The clock divider of claim 7 wherein the received clock signal is a clock of a phase-locked loop circuit.
9. The clock divider of claim 8 wherein said programmable delay line further comprises a multiplexer configured to select a delay from a plurality of delays across the chain of delay elements.
10. The clock divider of claim 9 wherein said first counter is an 8-bit down counter and wherein said second counter is a 24-bit up counter.
11. A method of dividing a frequency of a received clock signal by a number having an integer portion and a fractional portion, the method comprising:
generating, using a first counter, a first output signal at a first frequency, where the first frequency is based on the received clock signal and a first portion of the integer portion of the number;
generating, using a second counter coupled to the first counter, a second output signal at a second frequency, where the second frequency is based on the received clock signal and a second portion of the integer portion of the number, and where the second frequency is smaller than the first frequency; and
delaying the second output signal based on the fractional portion via a chain of delay elements.
12. The method of claim 11 further comprising:
counting from a first portion of the integer using a down counter.
13. The method of claim 12 wherein the down counter is a roll counter.
14. The method of claim 12 further comprising:
counting from the second portion of the integer using an up counter.
15. The method of 14 wherein the up counter is enabled to increase its count only when the down counter reaches a terminal count.
16. The method of claim 15 further comprising:
inverting a stored value when the first counter reaches a count of 1 and the second counter reaches its terminal counts.
17. The method of claim 16 further comprising:
loading the first portion of the integer portion of the number into the first counter and the second portion of the integer portion of the number into the second counter when the first counter reaches a count of 1 and the second counter reaches its terminal counts.
18. The method of claim 17 wherein the received clock signal is a clock of a phase-locked loop circuit.
19. The method of claim 18 further comprising selecting a delay from a plurality of delays of the chain of delay elements in accordance with the fractional portion of the number.
20. The method of claim 19 wherein said first counter is an 8-bit down counter and wherein said second counter is a 24-bit up counter.