Phase controlled high speed interfaces
View Patent ↗A system and method are used to allow high speed communication between a chip and an external device. The system and method include a PLL with multiple phased outputs configured to be controlled digitally, a deskew PLL configured to align a clock of controller circuitry to interface circuitry, and a phase interpolated voltage controlled delay line configured to phase shift incoming signals. Analog design techniques of phase interpolation accurately position clocks and strobe signals that are required for high speed interfaces. The high speed interface is for transmitting and receiving signals from the external device, for example, a DDR DRAM.
1. A phase interpolator system, comprising:
a plurality of branches, each branch comprising
a phase interpolator that receives a clock signal and a control signal, which are distinct from one another, and that generates a phase shifted clock signal through phase shifting the received clock signal during a phase shifting operation, and
a divider that divides the phase shifted clock signal to produce an output clock signal.
2. The phase interpolator system of claim 1 , wherein during the phase shifting operation each of the phase interpolators performs:
a coarse shifting operation that establishes a base line phase shift value for the received clock signal, producing a coarsely phase shifted clock signal; and
a fine tuning shifting operation that shifts the coarsely phase shifted clock signal with respect to the established base line phase shift value, producing a finely phase shifted clock signal.
3. The phase interpolator system of claim 2 , wherein the base line phase shift value is about 0 degrees or about 90 degrees.
4. The phase interpolator system of claim 2 , wherein during the fine tuning shifting operation, an incremental phase shift between about +/−45 degrees or between about +/−90 degrees is performed with respect to the base line phase shift value.
5. The phase interpolator system of claim 4 , wherein a resolution of the incremental phase shift is based on a bit size of the control signal.
6. The phase interpolator system of claim 1 , wherein the divided phase shifted clock signal output from each of the plurality of branches has a same frequency.
7. The phase interpolator system of claim 1 , wherein during the phase shifting operation each of the phase interpolators:
selects a pair of the clock signals using the control signal, and
generates a weighted average for the phases of the pair of clock signals based on the control signal.
8. A method for producing a phase shifted output clock signal, comprising:
(a) coarsely phase shifting a phase of a received clock signal to establish a base line phase shift value based on a received phase control signal, which is distinct from the received clock signal; and
(b) incrementally phase shifting the coarsely shifted clock signal higher and lower than the established base line phase shift value.
9. The method of claim 8 , wherein the base line phase shift value is about 0 degrees or about 90 degrees.
10. The method of claim 8 , wherein step (b) comprises performing the incremental phase shifting between about +/−45 degrees or between about +/−90 degrees with respect to the base line phase shift value.
11. The method of claim 8 , wherein during step (b) a resolution of the incremental phase shift is based on a bit size of the phase control signal.
12. A phase interpolator system, comprising:
a plurality of branches, each branch comprising
a phase interpolator configured to:
receive a clock signal and a control signal, which are distinct from one another, and
generate a finely phase shifted clock signal through phase shifting the received clock signal during a phase shifting operation, the phase shifting operation comprising,
a coarse shifting operation that establishes a base line phase shift value for the received clock signal, producing a coarsely phase shifted clock signal, and
a fine tuning shifting operation that shifts the coarsely phase shifted clock signal with respect to the established base line phase shift value, producing the finely phase shifted clock signal; and
a divider that divides the finely phase shifted clock signal to produce an output clock signal.