DIGITAL TO ANALOG CONVERTER AND ANALOG TO DIGITAL CONVERTER CALIBRATION TECHNIQUES
Methods and devices for the calibration of digital to analog converters (DAC) and analog to digital converters (ADC) are disclosed. In a first step the DAC is calibrated and in a second step the calibrated DAC is used to calibrate the ADC. Averaging techniques and/or equation based techniques are used to further improve the calibration of both components in an iterative process. Embodiments of the invention allow for a very compact physical implementations of the converter. The invention reduces of analog circuitry in favor of digital circuits. Embodiments of the invention are suitable for the implementation in fine line CMOS processes and can operate in a low supply voltage environment.
This application is a Continuation-in-Part of U.S. patent application Ser. No. 14/280,574, filed May 17, 2014, entitled “Methods, devices, and algorithms for the linearization of nonlinear time variant systems and the synchronization of a plurality of such systems” which claims priority to U.S. Provisional Patent App. Ser. No. 61/825,030 filed May 18, 2013, and additionally claims the benefit of U.S. Provisional Patent App. Ser. No. 62/079,552 filed Nov. 14, 2014, the contents of each of which are hereby incorporated by reference.
TECHNICAL FIELDThe invention relates to the field of digital to analog (DAC) and analog to digital (ADC) converter. More particularly to the calibration of digital to analog and analog to digital converter using digital techniques.
BACKGROUNDSome applications require the integration of digital to analog converter and/or analog to digital converter together with digital circuits. Digital circuits consume less power and required less area in fine line CMOS process, i.e. processes below 100 nm. In many cases the choice of process technology is dictated by the constraints of the digital circuitry. However, analog and mixed signals circuits, like DACs and ADCs, suffer from the poor matching performance and the low power supply voltages of fine line CMOS processes. Applying conventional DAC/ADC design techniques in fine line CMOS processes result in inefficient designs.
In the case of current steering DAC architectures the analog output is represented by the sum of unit segment currents. The unit segment currents are steered either to the positive or to the negative output of the DAC. The steering is achieved by switching elements that are controlled by signals derived from the DAC input signal. The matching of these unit segments determines the performance of the DAC. Performance parameters such as, integral non linearity (INL), differential non linearity (DNL) and spurious free dynamic range (SFDR) are affected. One method to calibrate a DAC is to equalize all the unit segments. With this method the unit segments are compared to a reference segment. Trim currents are added or subtracted to the unit segment currents such that their value is close to the reference segment currents. This can be done in a background mode or in dedicated calibration cycle during which the DAC is not producing an output signal. Another approach is digital pre distortion (DPD). With DPD, the unit segments are measured and new input codes for the DAC are calculated based on the measured values of the unit segments.
SUMMARYEmbodiments of the invention comprise digital techniques to calibrate DACs and ADCs. In a first step the DAC is calibrated and in a second step the calibrated DAC is used to calibrate the ADC. Equation based or averaging techniques can be used to calibrate the DAC. The initial accuracy of the analog circuit is not critical. Iterative bootstrapping is used to improve the accuracy over time. Embodiments of the invention allow for a very compact physical implementation. Another aspect of the invention is the reduction of analog circuitry in favor of digital circuits. Digital circuits can be automatically generated from source code and therefore decreases the design time when porting the design into a new process technology. Embodiments of the invention can be implemented in low supply voltage environments.
The above summary of the invention is not intended to describe each illustrated embodiment or every implementation of the present invention. The detailed description and claims that follow more particularly exemplify these embodiments.
Advantages of embodiments of the present invention will be apparent from the following detailed description of exemplary embodiments thereof, which description should be considered in conjunction with the accompanying drawing:
While embodiments are amenable to various modifications and alternative forms, specifics thereof have been shown by way of example in the drawings and will be described in detail. It should be understood, however, that the intention is not to limit the invention to the particular embodiments described. On the contrary, the intention is to cover all modifications, equivalents, and alternatives falling within the spirit and scope of the invention as defined by the appended claims.
DETAILED DESCRIPTION OF THE DRAWINGSThe following disclosure relates to the implementation of the Main DAC, Reference DAC, subtractor block and detector block of
The use of an adder block or subtractor block depends on the use of the output signal of the main DAC compared with the reference DAC. If, for example, the main DAC is implemented as a current source and the reference DAC as a current sink then a adder would be used. If both are implemented as either current source or current sink then a subtractor would be used. Further, the main and reference DAC can be implemented as differential circuits. In this case the determination of adder or subtractor is made whether the positive and negative outputs are combined or if the opposite polarity outputs are combined.
In
This is the case when the output from the main DAC is used to drive a load signal which requires much more energy than the signal from the reference DAC and the main DAC has to be implemented in a technology which can sustain high voltages and/or current levels.
The reference DAC on the other hand is implemented in a process technology which can be energy efficient, has smaller mismatch errors and/or is the same process technology as the digital circuitry in front of the DAC.
The equations in
By sampling the system at different time points within a clock cycle the controller is able to collect more data of the system. This additional information can be used to estimate the segments errors. A sub-sampling system can be built by dividing the clock 242 down to operate the ADC at a lower sampling frequency. The reduced the sampling rate of the ADC can reduce the power consumption of the ADC and simplifies the ADC design.
The circuits of
Either resistor 717 or 722 can be made adjustable via switches adding parallel resistors on to resistors 717 and/or 722. The circuit in
A multi-level delta sigma ADC can also be realized with the circuit of
While the foregoing written description of the invention enables one of ordinary skill to make and use what is considered presently to be the best mode thereof, those of ordinary skill will understand and appreciate the existence of variations, combinations, and equivalents of the specific embodiment, method, and examples herein. The invention should therefore not be limited by the above described embodiment, method, and examples, but by all embodiments and methods within the scope and spirit of the invention.
Various embodiments of systems, devices and methods have been described herein. These embodiments are given only by way of example and are not intended to limit the scope of the invention. It should be appreciated, moreover, that the various features of the embodiments that have been described may be combined in various ways to produce numerous additional embodiments. Moreover, while various materials, dimensions, shapes, configurations and locations, etc. have been described for use with disclosed embodiments, others besides those disclosed may be utilized without exceeding the scope of the invention.
Persons of ordinary skill in the relevant arts will recognize that the invention may comprise fewer features than illustrated in any individual embodiment described above. The embodiments described herein are not meant to be an exhaustive presentation of the ways in which the various features of the invention may be combined. Accordingly, the embodiments are not mutually exclusive combinations of features; rather, the invention can comprise a combination of different individual features selected from different individual embodiments, as understood by persons of ordinary skill in the art. Moreover, elements described with respect to one embodiment can be implemented in other embodiments even when not described in such embodiments unless otherwise noted. Although a dependent claim may refer in the claims to a specific combination with one or more other claims, other embodiments can also include a combination of the dependent claim with the subject matter of each other dependent claim or a combination of one or more features with other dependent or independent claims. Such combinations are proposed herein unless it is stated that a specific combination is not intended. Furthermore, it is intended also to include features of a claim in any other independent claim even if this claim is not directly made dependent to the independent claim.
Any incorporation by reference of documents above is limited such that no subject matter is incorporated that is contrary to the explicit disclosure herein. Any incorporation by reference of documents above is further limited such that no claims included in the documents are incorporated by reference herein. Any incorporation by reference of documents above is yet further limited such that any definitions provided in the documents are not incorporated by reference herein unless expressly included herein.
For purposes of interpreting the claims for the present invention, it is expressly intended that the provisions of Section 112, sixth paragraph of 35 U.S.C. are not to be invoked unless the specific terms “means for” or “step for” are recited in a claim.
Claims
1. A signal processing circuit comprising:
- a first digital to analog converter configured to receive an input signal and generate a corresponding output signal;
- a second digital to analog converter based on a segmented architecture configured to receive the input signal an generate a corresponding reference signal;
- a combiner configured to receive the output signal form the first and second digital to analog converter and generating a corresponding error signal;
- an analog to digital converter connected to receive the error signal and generate a digital error signal; and
- a controller connected to receive the digital error signal and the input signal and generate at least one control signals, wherein each of the at least one control signals can be routed by the controller to one or more of the first digital to analog converter the second digital to analog converter, the combiner and the analog to digital converter,
- wherein the controller is configured to shuffle the segments in the second digital to analog converter between samples of the input signal.
2. The signal processing circuit according to claim 1, wherein the controller is configured to collect a set of samples from the digital error signal and the input signal and compute a correction signal for one or more of the first digital to analog converter, the second digital to analog converter, and the analog to digital converter.
3. The signal processing circuit according to claim 1, wherein the controller is configured to shuffle the segments in the first and/or second digital to analog converter, build a set of equations based a set of equations based on the segments activated in the first and second digital to analog converter and the associated digital error values over a set of input samples, and solves the equations for the segment values.
4. The signal processing circuit according to claim 1 further comprising:
- a delay block; and
- a clock generator configure to provide a clocking signal the first digital to analog converter, the second digital to analog converter and the delay block;
- wherein the delay block is configured to provide the clock signal for the analog to digital converter.
5. The signal processing circuit according to claim 1 further comprising:
- a clock divider; and
- a clock generator configure to provide a clocking signal for the first digital to analog converter, the second digital to analog converter, and the clock divider;
- wherein the clock divider is configured to provide the clock signal for the analog to digital converter.
6. The signal processing circuit according to claim 1, wherein the combiner includes a resistor coupled to the output signal and to a virtual ground node and configured to convert the output signal into an equivalent current flowing into the virtual ground node, and wherein the second digital to analog converter has a current domain output and the output of the second digital to analog converter is coupled to the virtual ground node and the difference between the equivalent current and the output current of the second digital to analog converter is use to drive the analog to digital converter.
7. The signal processing circuit according to claim 6, wherein the first and second digital to analog converters have differential outputs, the analog to digital converter has differential inputs, and the virtual ground node is differential.
8. The signal processing circuit according to claim 6, wherein the virtual ground comprises a trans-impedance amplifier, and wherein the difference between the equivalent current and the output current of the second digital to analog converter is converted to a voltage to drive the analog to digital converter.
9. The signal processing circuit according to claim 6, wherein the first digital to analog converter, the virtual ground, and the analog to digital converter are configured to function as one of a sub ranging analog to digital converter, a sigma delta analog to digital converter, and a dual slope analog to digital converter.
10. The signal processing circuit according to claim 1, wherein the first and/or second digital to analog converter has a pool of trim segments which are configured to be activated based on the input signal and a mapping function.
11. The signal processing circuit according to claim 1, wherein the first and/or second digital to analog converter is configured to:
- receive an input sample having least significant bits (LSB) and at least one most significant bit (MSB);
- generate an output current comprising a set of 2̂MSB−1 MSB segments and a set of at least 2*2̂LSB−1 LSB segments, each of the MSB segments and the LSB segments having either an activated or un-activated state; and
- replace a randomly selected activated MSB segment with 2̂LSB un-activated LSB segments.
12. A method of calibrating the linearity of a segmented digital to analog converter comprising:
- converting with a first segmented digital to analog converter a digital input signal into an analog output signal, wherein the mapping of the input code to the activated segments is deterministic;
- converting with a second segmented digital to analog converter the digital input signal into an analog reference signal, wherein the mapping of the input code to the activated segments is pseudo random;
- forming an analog error signal by subtracting the analog output signal from the analog reference signal;
- converting the analog error signal with an analog to digital converter into an digital error signal;
- collecting a set of digital error signal samples and the associated input signals samples; and
- correcting the output of the first and/or second digital to analog converter based on the collected digital error signals.
13. The method of claim 12, further comprising the steps of:
- recording the active segments for each input sample of the set of input samples for the first analog to digital converter;
- recording the active segments for each input sample of the set of input samples for the second analog to digital converter;
- forming a set of equations with the set of active segments from the first and second analog to digital converters and the set of error signals samples;
- solving the set of equations for the segments values of the first and second digital to analog converter; and
- correcting the output of the first and/or second digital to analog converter based on the calculated segment values.
14. The method of claim 12, further comprising the steps of:
- averaging the error signals for each input data code over a statistically significant set; and
- calculating the estimated segment values for the first digital to analog converter from the set of averaged error values.
15. The method of claim 12, wherein correcting the first and/or second digital to analog converter comprises implementing digital pre-distortion techniques.
16. The method of claim 12, wherein correcting the first and/or second digital to analog converter comprises modifying which of the segments are activated.
17. The method of claim 12, wherein correcting first and/or second digital to analog converter by adding at least one trim segment to the output based upon a mapping function.
18. The method of claim 12, further comprising calibrating the analog to digital converter by using the first and/or second digital to analog converter as reference.
19. The method of claim 12, further comprising forming a high resolution analog to digital converter by configuring the first digital to analog converter and the analog to digital converter to one of a sub-ranging, dual slope, delta sigma analog to digital converter.
20. The signal processing circuit according to claim 1, further comprising an analog signal processing block configured to receive the output signal of the first digital to analog converter and generate the output signal.
Type: Application
Filed: Nov 13, 2015
Publication Date: May 12, 2016
Inventor: Bernd Schafferer (Amesbury, MA)
Application Number: 14/941,206