Piecewise linear calibration method and circuit to correct transfer function errors of digital to analog converters
AssigneeTexas Instruments Incorporated
InventorsTurker Kuyel, Kumar Lakshmi Parthasarathy
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Abstract
A calibrated digital-to-analog converter (DAC) (15′) has a main DAC (17) having a digital input and an analog output. An on-chip memory (21) stores measured INL values of the main DAC at a few selected input codes, and digital interpolation (50,17) is used to approximate INL error values at all input codes (14 . . . 14VI). To cancel the INL errors of the main DAC, outputs of this digital interpolation are sent to a calibration DAC (19), which has an analog output subtracted from the analog output of the main DAC. This subtraction can also be done in the digital domain, removing the need for a calibration-DAC when a main DAC with higher bit-count is designed.
Claims35
A method for constructing a calibrated digital-to-analog converter (DAC), comprising:
- developing predetermined functions between adjacent pairs of selected digital input code values approximating deviations of actual analog output values of a main DAC from desired analog output values of said main DAC;
- and configuring a programmable circuit to provide digital correction input values to a calibration DAC according to said predetermined functions, wherein said calibration DAC provides analog correction values for subtraction from an analog output of said main DAC to provide calibrated analog output values.
A method for constructing a calibrated digital-to-analog converter (DAC), comprising:
- developing piecewise linear functions between adjacent pairs of selected digital input code values approximating deviations of actual analog output values of a main DAC from desired analog output values of said main DAC;
- and configuring a programmable circuit to provide digital correction input values to a calibration DAC according to said piecewise linear functions, wherein said calibration DAC provides analog correction values for subtraction from an analog output of said main DAC to provide calibrated analog output values.
A method for constructing a calibrated digital-to-analog converter (DAC), comprising:
- providing an uncalibrated main DAC having a digital input and an analog output, wherein when digital input signal values are applied to said digital input, corresponding analog output values are produced on said analog output;
- measuring a deviation of an actual analog output value from a desired analog output value for each of a number of digital input code values;
- developing sets of linearly varying values between adjacent pairs of selected digital input code values, wherein said sets approximate said measured nonlinearity values;
- and configuring a programmable circuit to provide digital correction input values to a calibration DAC according to said linearly varying values, wherein when a digital input code value is applied to said digital input of said main DAC, an analog output of said calibration DAC is subtracted from the analog output of said main DAC to provide a calibrated output value.
A method for constructing a digital-to-analog converter (DAC), comprising:
- constructing an uncalibrated DAC that includes a circuit for producing an analog output signal having a magnitude that corresponds to a digital input according to a predetermined digital input signal code, wherein a predetermined sequence of digital input signal codes produces corresponding analog output values according to an actual transfer function, memory, and digital circuits configured to modify said digital input signal codes according to states contained in said memory;
- for each of predetermined digital input code values, determining a corresponding error value representing a deviation of an actual value of said analog output produced by said actual transfer function from a desired analog output value according to a desired transfer function;
- coding states into said memory representing said corresponding error values;
- and operating said digital circuits to modify said predetermined digital input codes according to said states in said memory to produce the desired analog output values.
A calibrated digital-to-analog converter (DAC), comprising:
- a main DAC having a digital input and an analog output, wherein when digital input signal values are applied to said digital input, corresponding analog output values are produced on said analog output;
- a memory containing sets of linearly varying values between adjacent pairs of selected digital input code values, wherein said sets approximate deviations of actual analog output values from desired analog output values;
- a calibration DAC having an analog output connected to be subtracted from the analog output of said main DAC;
- and a control circuit to select values from said sets of linearly varying values corresponding to input digital values to said main DAC and apply said selected values to said calibration DAC.
A calibrated digital-to-analog converter (DAC), comprising:
- a main DAC having a digital input and an analog output, wherein when digital input signal values are applied to said digital input, corresponding actual analog output values are produced on said analog output;
- a memory containing control point data;
- wherein each control point is spaced from an adjacent control point to contain a predetermined range of actual analog output values;
- circuitry for generating linearly varying deviation values between said actual analog output values at each adjacent pair of said control points;
- a calibration DAC having an analog output connected to be subtracted from the actual analog output value of said main DAC;
- and a control circuit to select a value from said linearly varying deviation values corresponding to said actual analog output value, said selected deviation value being interpolated from deviation values between adjacent control points within the range of which said actual analog output value lies, and to apply said selected value to said calibration DAC.
Dependencies are inferred from the claim text.