Self-compensating digital-to-analog converter and methods of calibration and operation thereof
Cost-effective structures and methods that allow an integrated digital-to-analog converter (DAC) to simultaneously achieve wide dynamic ranges and bandwidths through the use of built-in measurement and compensation mechanisms that are primarily digital. The measurements of the DAC's distortions are made with a relatively simple analog-to-digital converter (ADC) that is not designed to accommodate the combination of the bandwidth and the resolution offered by the DAC, but is nonetheless sufficient in determining the characteristics of the DAC's impairments during a calibration procedure. This information is then used in a feed-forward compensation system during the DAC's normal operation to estimate and cancel the distortions in its output signal that could result from the various impairments.
1. A self-calibrating digital-to-analog converter (DAC), comprising:
at least one DAC core operable to receive digital data words and clock pulses and produce an analog output having at least one impairment;
an analog function block coupled to said at least one DAC core and operable to receive and make measurements of said at least one impairment;
an analog-to-digital converter (ADC) coupled to said analog function block and operable to digitize said measurements during a calibration phase of operation of said self-calibrating DAC, said ADC operating at a sampling rate that is substantially lower than the DAC's clocking rate; and
a digital controller coupled to said at least one DAC core and said ADC and operable to employ said measurements to adjust at least one of said digital data words and said clock pulses to mitigate the effects of said at least one impairment by adjusting either a timing, duration, or combination thereof, of said at least one of said clock pulses in accordance with at least a remainder of a predicted error.
2. The DAC as recited in claim 1 wherein said analog function block is operable to carry out one or both of:
a linear filter function, and
a non-linear function.
3. The DAC as recited in claim 1 wherein said digital controller is further configured to determine correction signals that are to be applied through digital and analog amplitude compensation paths and a remaining error to be corrected through use of time-domain manipulation of said clock pulses.
4. The DAC as recited in claim 1 wherein said digital controller is further operable to compensate by manipulating said digital data words and said clock pulses in the time domain.
5. The DAC as recited in claim 4 wherein said digital controller is further operable to adjust instances at which particular digital words are applied to a conversion element of said DAC.
6. The DAC as recited in claim 1 wherein said digital controller is further operable to compensate for said at least one impairment by applying controlled current/voltage-based corrections to said output.
7. The DAC as recited in claim 6 wherein said digital controller is further operable to adjust a duration of a pulse that determines how long a conversion element of said DAC would produce a certain corresponding current/voltage.
8. The DAC as recited in claim 1 wherein said digital controller is further operable to attenuate said at least one impairment by applying an inverted estimated error signal.
9. The DAC as recited in claim 8 wherein said digital controller is further operable to attenuate said at least one impairment by applying an inverted estimated error signal before combining time-domain manipulations.
10. The DAC as recited in claim 1 wherein said DAC is a binary DAC.
11. The DAC as recited in claim 1 wherein said DAC is a segmented DAC.
12. The DAC as recited in claim 1 wherein said DAC is an interleaved DAC with identical branches.
13. The DAC as recited in claim 1 wherein said DAC is an interleaved DAC with different branches.
14. The DAC as recited in claim 1 wherein said DAC is part of a Data Over Cable System Interface Specification (DOCIS) head-end transmitter.
15. The DAC as recited in claim 1 wherein said DAC is part of a Multimedia Over Cable Alliance (MOCA) transmitter.
16. The DAC as recited in claim 1 wherein said DAC is part of a cognitive radio transceiver.
17. The DAC as recited in claim 1 wherein said DAC is part of one selected from the group consisting of:
an instrument,
a pulse-forming circuit for a radar, and
a software-defined jammer.
18. The DAC as recited in claim 1 wherein said DAC is part of a network selected from the group consisting of:
a 4G network,
an LTE network, and
a wireless LAN.
19. A method of calibrating a digital-to-analog converter (DAC), comprising:
intermittently stimulating a tested element to an input of said DAC;
operating said DAC to produce an output signal;
using an analog-to-digital converter (ADC) operating at substantially lower sampling rates than the clocking rate of said DAC to determine amplitude errors in said output signal caused by a presence of said tested element;
using said ADC to determine amplitude errors in said output signal experienced during said intermittently stimulating of said tested element; and
adjusting a determined pulse duration and determined timing in accordance with at least a remainder of a predicted error.
20. The method as recited in claim 19 further comprising storing said static amplitude errors and said dynamic amplitude errors in at least one table.
21. The method as recited in claim 19 further comprising periodically repeating said intermittently coupling, said operating, said using said ADC to determine said static amplitude errors and said using said ADC to determine said dynamic amplitude errors.
22. The method as recited in claim 19 further comprising recording a temperature of said DAC during said operating.
23. The method as recited in claim 22 further comprising:
storing said temperature with said static amplitude errors and said dynamic amplitude errors; and
employing said static amplitude errors and said dynamic amplitude errors when said DAC is subsequently operating at least proximate said temperature; and employing modified versions of said static amplitude errors and said dynamic amplitude errors that are calculated based on known or estimated temperature dependencies.
24. The method as recited in claim 19 further comprising producing an indication that said calibrating is complete.
25. A self-calibrating method for a digital-to-analog converter (DAC), comprising:
determining a partition for correction of instantaneous error among digital amplitude, analog amplitude and pulse duration and timing;
applying a corresponding digital amplitude correction via a digital summer;
applying a corresponding analog amplitude correction via a dedicated compensation DAC; and
adjusting said pulse duration and timing in accordance with at least a remainder of a predicted error.
26. The method as recited in claim 25 wherein said DAC is a binary DAC.
27. The method as recited in claim 25 wherein said DAC is a segmented DAC.
28. The method as recited in claim 25 wherein said DAC is an interleaved DAC with identical branches.
29. The method as recited in claim 25 wherein said DAC is an interleaved DAC with different branches.
30. The method as recited in claim 25 wherein said partition is an optimized to minimize the resultant error.