Method and system for time interleaved digital to analog conversion for a cable modem
Provided is a transmitter in a communications system including a plurality of digital to analog converters. Also included is a plurality of clocks, each being communicably coupled to a corresponding one of the digital to analog converters.
1. A transmitter in a communications system, comprising:
a plurality of digital to analog converters (DACs);
an input of each DAC within the plurality (i) being respectively coupled to an output of only one corresponding phase adjuster and (ii) configured to receive an output from the phase adjuster and a corresponding digital input signal; and
only one phase-locked loop coupled to the plurality of DACs and the phase adjusters;
wherein outputs of the DACs are combined to form a single output analog signal representative of the digital input signals.
2. The transmitter of claim 1 , wherein the communications system includes a cable modem; and
wherein the cable modem includes the transmitter.
3. The transmitter of claim 1 , wherein the cable modem is deployed in an upstream communications channel.
4. The transmitter of claim 1 , further comprising:
a plurality of clock generators each being communicably coupled to a corresponding one of the DACs, wherein each clock generator provides a clock signal at a first frequency originating from the phase-locked loop to its corresponding DAC.
5. The transmitter according to claim 4 ,
wherein each of the provided clock signals is shifted in phase from all of the other clock signals such that an effective sampling rate of the plurality of DACs is a multiple of the first frequency.
6. The transmitter according to claim 5 , wherein each of the phases of the provided clock signals differs from the other phases by a multiple of about 90 degrees.
7. The transmitter according to claim 6 , wherein the plurality of DACs are configured to provide time-interleaved conversion.
8. The transmitter according to claim 7 , wherein each of the clock generators includes a divider circuit.
9. The transmitter according to claim 8 , wherein the divider circuit is configured to divide by an integer multiple of two.
10. The transmitter according to claim 8 , wherein each of the clock generators includes a phase interpolator couple to the divide circuit.
11. The transmitter of claim 4 , wherein each of the DACs is of a 10 bit variety.
12. The transmitter of claim 4 , wherein the communications system includes a cable modem.
13. The transmitter of claim 12 , wherein the cable modem is a deployed in an upstream communications channel.
14. A method comprising:
producing a plurality of phase shifted clock signals, each clock signal originating from a corresponding phase adjuster, all of the phase adjusters being coupled to only one phase-locked loop;
clocking each of a corresponding plurality of received external input digital signals with a corresponding one of the phase shifted clock signals; and
providing each of the clocked digital input signals and the corresponding phase shifted clock signals as an input to a corresponding digital to analog converter (DAC), the DACs being coupled to the phase adjusters and the phase-locked loop, outputs of the DACs being combined to form a single output analog signal representative of the digital input signals.
15. The method of claim 14 , wherein each of phases of the phase shifted clock signals differs from a phase of all of the other signals by a multiple of about 90 degrees.
16. The method of claim 14 , wherein the producing step comprises:
interpolating a plurality of clock signals originating from the phase-locked loop; and
dividing each of the plurality clock signals to create the phase shifted clock signals.
17. The method of claim 14 , wherein an effective sampling rate of the plurality of received digital signals is a multiple of a frequency of the phase shifted clock signals.
18. The method of claim 17 , wherein the effective sampling rate is a product of the frequency of the phase shifted clock signals and a number of received digital signals in the plurality of received digital signals.
19. The transmitter of claim 1 , wherein an effective sampling rate of the plurality of DACs is a product of a first frequency and a number of DACs in the plurality of DACs.
20. The transmitter of claim 4 , wherein an effective sampling rate of the plurality of DACs is a product of a first frequency and a number of DACs in the plurality of DACs.