Calibration of interpolating string digital-to-analog converters

Patent metadata

Field	Value
Publication number	US-9621177-B1
Application number	US-201615152384-A
Country	US
Kind code	B1
Filing date	May 11, 2016
Priority date	Dec 8, 2015
Publication date	Apr 11, 2017
Grant date	Apr 11, 2017

Abstract

Methods, apparatus and articles of manufacture (e.g., physical storage media) to calibrate interpolating string digital-to-analog converters are disclosed. Example methods disclosed herein to calibrate a digital-to-analog converter (DAC) include determining a first calibration codeword based on a first nonlinearity error value measured at an output of the DAC when a most-significant-bit (MSB) portion of an input codeword is applied to an input of the DAC. Such disclosed example methods also include determining a second calibration codeword based on a second measured nonlinearity error value measured at the output of the DAC when a least-significant-bit (LSB) portion of the input codeword is applied to the input of the DAC. Such disclosed example methods further include combining the first calibration codeword and the second calibration codeword to determine a third calibration codeword to be accessed by the DAC to calibrate the output of the DAC when the input codeword is applied to the DAC.

First claim

What is claimed is:

1. A method to calibrate a digital-to-analog converter (DAC), the method comprising:
determining a first calibration codeword based on a first nonlinearity error value measured at an output of the DAC when a most-significant-bit (MSB) portion of an input codeword is applied to an input of the DAC;
determining a second calibration codeword based on a second measured nonlinearity error value measured at the output of the DAC when a least-significant-bit (LSB) portion of the input codeword is applied to the input of the DAC; and
combining the first calibration codeword and the second calibration codeword to determine a third calibration codeword to be accessed by the DAC to calibrate the output of the DAC when the input codeword is applied to the DAC;

wherein the DAC is an interpolating string DAC including a main coarse string DAC circuit and a main interpolator circuit, the MSB portion of the input codeword corresponds to a number of bits of resolution of the main coarse string DAC circuit, and the LSB portion of the input codeword corresponds to a number of bits of resolution of the main interpolator circuit.

2. A method as defined in claim 1 , wherein the DAC further includes a calibration coarse string DAC circuit and a calibration interpolator circuit, and further including storing the third calibration codeword in a codeword storage of the interpolating string DAC, the interpolating string DAC to retrieve and apply the third calibration codeword to the calibration coarse string DAC circuit and the calibration interpolator circuit of the interpolating string DAC to calibrate the output of the interpolating string DAC when the input codeword is applied to the interpolating string DAC.

3. A method as defined in claim 2 , wherein determining the first calibration codeword includes:
multiplying the first nonlinearity error value by a ratio of a full range of the calibration interpolator circuit divided by a calibration step size of the calibration interpolator circuit to determine an intermediate value; and
setting the first calibration codeword to be a next lowest integer less than or equal to the intermediate value.

4. A method as defined in claim 2 , wherein determining the second calibration codeword includes:
dividing the second nonlinearity error value by a calibration step size of the calibration interpolator circuit to determine an intermediate value; and
setting the second calibration codeword to be a next lowest integer less than or equal to the intermediate value.

5. A method to calibrate a digital-to-analog converter (DAC), the method comprising:
determining a first calibration codeword based on a first nonlinearity error value measured at an output of the DAC when a most-significant-bit (MSB) portion of an input codeword is applied to an input of the DAC;
determining a second calibration codeword based on a second measured nonlinearity error value measured at the output of the DAC when a least-significant-bit (LSB) portion of the input codeword is applied to the input of the DAC; and
combining the first calibration codeword and the second calibration codeword to determine a third calibration codeword to be accessed by the DAC to calibrate the output of the DAC when the input codeword is applied to the DAC;

further including:
calculating a third nonlinearity error value based on the first nonlinearity error value and the second nonlinearity error value, the third nonlinearity error value corresponding to an uncalibrated output value that would be output from the DAC if the input codeword is applied to the input of the DAC without calibration being performed; and
calculating a fourth nonlinearity error value based on the first nonlinearity error value, the first calibration codeword, the second nonlinearity error value and the second calibration codeword, the fourth nonlinearity error value corresponding to a calibrated output value that would be output from the DAC if the input codeword is applied to the input of the DAC with calibration being performed.

6. A digital-to-analog converter (DAC) calibrator comprising:
a first codeword calibrator to determine a first calibration codeword based on a first nonlinearity error value measured at an output of a DAC when a most-significant-bit (MSB) portion of an input codeword is applied to an input of the DAC;
a second codeword calibrator to determine a second calibration codeword based on a second measured nonlinearity error value measured at the output of the DAC when a least-significant-bit (LSB) portion of the input codeword is applied to the input of the DAC; and
a calibration codeword combiner to combine the first calibration codeword and the second calibration codeword to determine a third calibration codeword to be accessed by the DAC to calibrate the output of the DAC when the input codeword is applied to the DAC;
wherein the DAC is an interpolating string DAC including a main coarse string DAC circuit and a main interpolator circuit, the MSB portion of the input codeword corresponds to a number of bits of resolution of the main coarse string DAC circuit, and the LSB portion of the input codeword corresponds to a number of bits of resolution of the main interpolator circuit.

7. A DAC calibrator as defined in claim 6 , wherein the DAC further includes a calibration coarse string DAC circuit and a calibration interpolator circuit, and the calibration codeword combiner is further to store the third calibration codeword in a codeword storage of the interpolating string DAC, the interpolating string DAC to retrieve and apply the third calibration codeword to the calibration coarse string DAC circuit and the calibration interpolator circuit of the interpolating string DAC to calibrate the output of the interpolating string DAC when the input codeword is applied to the interpolating string DAC.

8. A DAC calibrator as defined in claim 7 , wherein the first codeword calibrator is to determine the first calibration codeword by:
multiplying the first nonlinearity error value by a ratio of a full range of the calibration interpolator circuit divided by a calibration step size of the calibration interpolator circuit to determine an intermediate value; and
setting the first calibration codeword to be a next lowest integer less than or equal to the intermediate value.

9. A DAC calibrator as defined in claim 7 , wherein the second codeword calibrator is to determine the second calibration codeword by:
dividing the second nonlinearity error value by a calibration step size of the calibration interpolator circuit to determine an intermediate value; and
setting the second calibration codeword to be a next lowest integer less than or equal to the intermediate value.

10. A digital-to-analog converter (DAC) calibrator comprising:
a first codeword calibrator to determine a first calibration codeword based on a first nonlinearity error value measured at an output of a DAC when a most-significant-bit (MSB) portion of an input codeword is applied to an input of the DAC;
a second codeword calibrator to determine a second calibration codeword based on a second measured nonlinearity error value measured at the output of the DAC when a least-significant-bit (LSB) portion of the input codeword is applied to the input of the DAC; and
a calibration codeword combiner to combine the first calibration codeword and the second calibration codeword to determine a third calibration codeword to be accessed by the DAC to calibrate the output of the DAC when the input codeword is applied to the DAC;

further including a nonlinearity measurer to:
measure the first nonlinearity error value and the second nonlinearity error value;
calcul

Assignees

• Texas Instruments Inc

Inventors

• Jun Zhang
• Wang Xuan
• Ou Dongyu
• Zhang Elliott
• Cao Echo

Classifications

• H03M1/66

  Digital/analogue converters ({H03M1/001 – } H03M1/10 take precedence) · CPC title

• H03M1/00

  Analogue/digital conversion; Digital/analogue conversion (conversion of analogue values to or from differential modulation H03M3/00) · CPC title

• H03M1/1033 Primary

  over the full range of the converter, e.g. for correcting differential non-linearity · CPC title

• H03M1/747

  with equal currents which are switched by unary decoded digital signals · CPC title

• H03M1/12

  Analogue/digital converters ({H03M1/001 – } H03M1/10 take precedence) · CPC title