Double-balanced sinusoidal mixing phase interpolator circuit and method
View Patent ↗A double-balanced sinusoidal mixing phase interpolator circuit comprises: a double-balanced gain stage having a first input for receiving a first phasor clock, a second input for receiving a second phasor clock, and a phase interpolator (PI) output, wherein the double-balance gain stage includes (i) a first gain stage having a positive input side and a negative input side for the first phasor clock and (ii) a second gain stage having a positive input side and a negative input side for the second phasor clock; and a sinusoidal digital-to-analog (DAC) stage coupled to the double-balanced gain stage and configured to implement sinusoidal weighting of positive and negative sides of differential DAC current for the first phasor clock and positive and negative sides of differential DAC current for the second phasor clock, wherein the sinusoidal weighting provides uniformly spaced phase steps in the phase interpolator (PI) output.
1. A double-balanced sinusoidal mixing phase interpolator comprising:
a double-balanced gain stage comprising:
a first input for receiving a first differential analog phasor clock signal,
a second input for receiving a second differential analog phasor clock signal;
a phase interpolator (PI) differential output having a first terminal and a second terminal;
a first gain stage comprising:
a first transistor having a first current electrode coupled to the first terminal of the PI output, a second current electrode, and a control electrode to receive a positive side of the first differential analog phasor clock signal;
a second transistor having a first current electrode coupled to the second terminal of the PI output, a second current electrode coupled to the second current electrode of the first transistor, and a control electrode to receive a negative side of the first differential analog phasor clock signal;
a third transistor having a first current electrode coupled to the first terminal of the PI output, a second current electrode, and a control electrode to receive the negative side of the first analog phasor clock signal; and
a fourth transistor having a first current electrode coupled to the second terminal of the PI output, a second current electrode coupled to the second current electrode of the third transistor, and a control electrode to coupled to receive the positive side of the first differential analog phasor clock signal;
a second gain stage comprising:
a fifth transistor having a first current electrode coupled to the first terminal of the PI output, a second current electrode, and a control electrode to receive a positive side of the second differential analog phasor clock signal;
a sixth transistor having a first current electrode coupled to the second terminal of the PI output, a second current electrode coupled to the second current electrode of the fifth transistor, and a control electrode to receive a negative side of the second differential analog phasor clock signal;
a seventh transistor having a first current electrode coupled to the first terminal of the PI output, a second current electrode, and a control electrode to receive the negative side of the second differential analog phasor clock signal; and
an eighth transistor having a first current electrode coupled to the second terminal of the PI output, a second current electrode coupled to the second current electrode of the seventh transistor, and a control electrode to receive the positive side of the second differential analog phasor clock signal; and
a sinusoidal digital-to-analog (DAC) stage coupled to the double-balanced gain stage and configured to implement sinusoidal weighting of positive and negative sides of first differential DAC current for the first differential analog phasor clock signal and positive and negative sides of second differential DAC current for the second differential analog phasor-clock signal according to a plurality of current adjustment steps, the current adjustment steps having a non-linear relationship, the sum of normalized amplitudes of the first and the second DAC currents being non-unity, wherein the sinusoidal weighting provides uniformly spaced phase steps in the phase interpolator (PI) output.
2. The interpolator of claim 1 , wherein the sinusoidal weighting further provides for intrinsic phase step linearity in the phase interpolator (PI) output across 360 degrees.
3. The interpolator of claim 1 , the double-balanced gain stage being configured to render a current mode logic (CML) gain of the first and second differential analog phasor clock signals nearly proportional to a current from the sinusoidal DAC stage.
4. The interpolator of claim 1 , wherein the first gain stage is configured to provide (i)(a) a positive side of differential DAC current and (i)(b) a negative side of differential DAC current for the first differential analog phasor clock, and wherein the second gain stage is configured to provide (ii)(a) a positive side of differential DAC current and (ii)(b) a negative side of differential DAC current for the second differential analog phasor clock.
5. The interpolator of claim 1 , wherein the phase interpolator output comprises (i) a positive output node and (ii) a negative output node.
6. The interpolator of claim 1 , wherein the first input includes a positive input node and a negative input node and wherein the second input includes a positive input node and a negative input node.
7. The interpolator of claim 1 , further wherein a tail current of the first and second transistors comprises the positive side of the first differential DAC current, a tail current of the third and fourth transistors comprises the negative side of the first differential DAC current, a tail current of the fifth and sixth transistors comprises the positive side of the second differential DAC current, and a tail current of the seventh and eighth comprises the negative side of the second differential DAC current.
8. The interpolator of claim 1 , wherein the first and second gain stages are coupled together for mixing the sinusoidally weighted first and second differential analog phasor clock signals.
9. The interpolator of claim 1 , wherein the sinusoidal DAC stage includes (i) a first DAC with bit-by-bit complementary current steering switches configured to sinusoidally weight the positive and negative sides of the first differential DAC current and (ii) a second DAC with bit-by-bit complementary current steering switches configured to sinusoidally weight the positive and negative sides of the second differential DAC current.
10. The interpolator of claim 9 , wherein the bit-by-bit complementary current steering switches of the first and second DAC are responsive to digital phase control code for rendering the positive and negative sides of the corresponding differential DAC currents.
11. The interpolator of claim 10 , wherein the digital phase control code comprises linear code configured to implement phase rotation.
12. The interpolator of claim 11 , wherein the linear code comprises thermometer-code with unary weighting.
13. The interpolator of claim 10 , wherein the digital phase control code intrinsically includes clock polarity selection for the phase interpolator (PI) output.
14. The interpolator of claim 9 , wherein each of the first and second DACs include a plurality of current cells, wherein the plurality of DAC current cells are sinusoidal weighted for providing a sinusoidal current in response to linear digital phase control code, and wherein the first and second DACs each comprises a plurality of complementary current steering switches and a plurality of sinusoidally weighted current cells, wherein the sinusoidal weighting is symmetrical about current cells within the middle of the plurality of current cells, the sinusoidal weighting further including scaling from the middle of the plurality of current cells in a sinusoidal manner to each end of the plurality of cells.
15. The interpolator of claim 1 , wherein a first current-steering digital-to-analog converter (DAC) is configured to provide in-phase (I) clock weighting, and a second current-steering digital-to-analog converter (DAC) is configured to provide quadrature (Q) clock weighting.
16. The interpolator of claim 1 , wherein the double-balanced gain stage implements sinusoidal mixing of input in-phase (I) and quadrature (Q) phased clocks.
17. The interpolator of claim 1 , wherein the double balanced gain stage is configured to generate a nearly one-to-one mapping between DAC current and current-mode-logic (CML) AC gain, wherein the nearly one-to-one mapping comprises a gain index on the order of 0.9-1.0.
18. A method for implementing double-balanced sinusoidal mixing phase interpolation comprising:
providing a double-balanced gain stage having a first input for receiving a first phasor clock, a second input for receiving a second phasor clock, and a phase interpolator (PI) output, wherein the double balanced gain stage includes: a first input for receiving a first differential analog phasor clock signal,
a second input for receiving a second differential analog phasor clock signal;
a phase interpolator (PI) differential output having a first terminal and a second terminal;
a first gain stage comprising:
a first transistor having a first current electrode coupled to the first terminal of the PI output, a second current electrode, and a control electrode to receive a positive side of the first differential analog phasor clock signal;
a second transistor having a first current electrode coupled to the second terminal of the PI output, a second current electrode coupled to the second current electrode of the first transistor, and a control electrode to receive a negative side of the first differential analog phasor clock signal;
a third transistor having a first current electrode coupled to the first terminal of the PI output, a second current electrode, and a control electrode to receive the negative side of the first analog phasor clock signal; and
a fourth transistor having a first current electrode coupled to the second terminal of the PI output, a second current electrode coupled to the second current electrode of the third transistor, and a control electrode to coupled to receive the positive side of the first differential analog phasor clock signal;
a second gain stage comprising:
a fifth transistor having a first current electrode coupled to the first terminal of the PI output, a second current electrode, and a control electrode to receive a positive side of the second differential analog phasor clock signal;
a sixth transistor having a first current electrode coupled to the second terminal of the PI output, a second current electrode coupled to the second current electrode of the fifth transistor, and a control electrode to receive a negative side of the second differential analog phasor clock signal;
a seventh transistor having a first current electrode coupled to the first terminal of the PI output, a second current electrode, and a control electrode to receive the negative side of the second differential analog phasor clock signal; and
an eighth transistor having a first current electrode coupled to the second terminal of the PI output, a second current electrode coupled to the second current electrode of the seventh transistor, and a control electrode to receive the positive side of the second differential analog phasor clock signal; and
providing a sinusoidal digital-to-analog (DAC) stage coupled to the double-balanced gain stage and configured to implement sinusoidal weighting of positive and negative sides of first differential DAC current for the first differential analog phasor clock signal and positive and negative sides of second differential DAC current for the second differential analog phasor clock signal according to a plurality of current adjustment steps, the current adjustment steps having a non-linear relationship, the sum of normalized amplitudes of the first and the second DAC currents being non-unity, wherein the sinusoidal weighting provides uniformly spaced phase steps in the phase interpolator (PI) output.