Method and apparatus for aligning and integrating serial data streams
An integrated circuit is incorporated into a communications system to enable a channel to achieve data rates that are at least double that which are currently achievable. The integrated circuit combines serial data signals using recovered clock and serial data signals in reference and non-reference clock domains. The integrated circuit rate converts recovered serial data in one of the clock domains, performs a phase alignment at the converted data rate, and returns the rate converted and phase-aligned serial data to the recovered data rate in response to the recovered clock from the remaining clock domain. Thereafter, the recovered and aligned serial data signals are combined. The phase alignment is monitored in circuitry that detects when a threshold offset is violated. When the threshold offset is violated a synchronization circuit is enabled.
1. A method for combining serial data streams, the method comprising:
in an interface having N input terminals and N/2 output terminals, receiving N serial data signals having a first data rate, wherein N is an even integer;
recovering a first serial data signal received at a first of the N input terminals to generate a first clock signal operating at the first data rate in a first clock domain;
dividing the first clock signal to generate a second clock signal operating at a second data rate in the first clock domain;
applying a first set of recovered data signals at respective inputs of a first 2×1 multiplexer to generate a representation of the first serial data signal;
recovering a second serial data signal received at a second of the N input terminals to generate a third clock signal operating at the first data rate in a second clock domain;
dividing the third clock signal to generate a fourth clock signal operating at the second data rate in the second clock domain;
applying a second set of recovered data signals at respective inputs of a 1×M demultiplexer operating in accordance with the fourth clock signal to generate a first representation of the second serial data signal, where M is an even integer;
applying the first representation of the second serial data signal at an input of a 1×M multiplexer operating in accordance with the second clock signal to generate a second representation of the second serial data signal; and
applying the representation of the first serial data signal and the second representation of the second serial data signal to the inputs of a second 2×1 multiplexer operating in accordance with the first clock signal to generate a combined serial data signal.
2. The method of claim 1 , wherein the step of applying a first set of recovered data signals at respective inputs of a first 2×1 multiplexer to generate a representation of the first serial data signal is accomplished in accordance with the second clock signal.
3. The method of claim 1 , further comprising:
aligning the second clock signal and the fourth clock signal.
4. The method of claim 3 , wherein aligning the second clock signal and the fourth clock signal is performed after confirming that a first clock and data recovery circuit and a second clock and data recovery circuit are frequency locked.
5. The method of claim 3 , wherein aligning the second clock signal and the fourth clock signal is performed after confirming that a first clock and data recovery circuit and a second clock and data recovery circuit are both frequency locked and phase locked.
6. An integrated circuit, comprising:
a first signal interface having N input terminals for receiving N serial data signals having a first data rate, the first signal interface including clock and data recovery circuitry that generates a set of recovered serial data streams for each of the N serial data signals, a recovered clock, and a divided clock in each of N clock domains, where N is a positive even integer;
reference circuitry coupled to receive the set of recovered serial data signals from a first member of a pair of input terminals and arranged to receive a reference clock responsive to a representation of the first data rate in a reference clock domain and to generate a representation of the serial data signal received at the first member of the pair of input terminals;
non-reference circuitry coupled to receive the set of recovered serial data signals from the remaining member of the pair of input terminals and arranged to generate a representation of the serial data signal received at the remaining member of the pair of input terminals, the representation operative at a second data rate in a non-reference clock domain;
rate conversion circuitry coupled to receive the representation of the serial data signal received at the remaining member of the pair of input terminals from the non-reference circuitry and the reference clock from the reference circuitry, the rate conversion circuitry arranged to generate a rate converted representation of the serial data signal received at the remaining member of the pair of input terminals;
synchronization circuitry for adjusting a phase margin between the reference clock and the non-reference clock as applied to the non-reference circuitry and the rate conversion circuitry; and
signal integration circuitry coupled to receive the recovered clock, the representation of the serial data signal received at the first member of the pair of input terminals, and the rate converted representation of the serial data signal received at the remaining member of the pair of input terminals and arranged to generate a combined serial data signal.
7. The integrated circuit of claim 6 , further comprising:
a second signal interface having N−1 output terminals for communicating the combined serial data signal.
8. The integrated circuit of claim 7 , wherein the combined serial data signal operates at a third data rate different from the first data rate and the second data rate.
9. The integrated circuit of claim 8 , wherein the third data rate is twice the first data rate.
10. The integrated circuit of claim 6 , wherein the synchronization circuitry includes a reset buffer responsive to a reset control signal and arranged to generate a buffered version of the reset control signal, a latch coupled to receive the buffered version of the reset control signal and the recovered clock, the latch arranged to generate a latched reset signal, and a multiplexer coupled to receive a low logic signal at a first input, the recovered clock at a second input, and the latched reset signal at a select input, the multiplexer arranged to generate a multiplexed clock signal.
11. The integrated circuit of claim 10 , wherein the synchronization circuitry further includes a clock divider arranged to generate a sub-divided clock signal.
12. The integrated circuit of claim 11 , wherein the clock divider is a multiple stage clock divider.
13. The integrated circuit of claim 12 , wherein the clock divider includes at least L stages, where L is an integer greater than 2.
14. The integrated circuit of claim 13 , wherein L is four.
15. The integrated circuit of claim 11 , further comprising:
alignment detection circuitry coupled to receive a divided clock in the reference clock domain, a divided clock in the non-reference clock domain and the sub-divided clock signal from the synchronization circuitry, the alignment detection circuitry arranged to generate an alignment control signal in response to a detected offset.
16. The integrated circuit of claim 15 , wherein the synchronization circuitry is responsive to the alignment control signal.
17. The integrated circuit of claim 15 , wherein the alignment detection circuitry includes a first pointer responsive to a first counter and arranged to generate a first value, a second pointer responsive to a second counter and arranged to generate a second value, and a comparator responsive to the subdivided clock and arranged to create the alignment control signal.
18. The integrated circuit of claim 17 , wherein the comparator is responsive to a threshold value.
19. The integrated circuit of claim 18 , wherein the threshold value is programmable.
20. The integrated circuit of claim 18 , wherein the threshold value is predetermined.