U.S. patent application number 14/266193 was filed with the patent office on 2015-11-05 for systems and methods for data conversion.
The applicant listed for this patent is Michael T. Berens, James R. Feddeler. Invention is credited to Michael T. Berens, James R. Feddeler.
Application Number | 20150318862 14/266193 |
Document ID | / |
Family ID | 54355970 |
Filed Date | 2015-11-05 |
United States Patent
Application |
20150318862 |
Kind Code |
A1 |
Feddeler; James R. ; et
al. |
November 5, 2015 |
SYSTEMS AND METHODS FOR DATA CONVERSION
Abstract
Systems and methods for electronically converting an analog
signal to a digital signal are disclosed. The systems and methods
may include, for a first bit value, setting a first conversion
value to include a first offset; using the output of a first
comparison, setting a second conversion value; and if the first bit
value has a predetermined relationship to the first offset bit
value, removing the first offset from the second conversion value,
and, using the output of a second comparison, setting a third
conversion value.
Inventors: |
Feddeler; James R.; (Austin,
TX) ; Berens; Michael T.; (Austin, TX) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Feddeler; James R.
Berens; Michael T. |
Austin
Austin |
TX
TX |
US
US |
|
|
Family ID: |
54355970 |
Appl. No.: |
14/266193 |
Filed: |
April 30, 2014 |
Current U.S.
Class: |
341/155 |
Current CPC
Class: |
H03M 1/0675 20130101;
H03M 1/069 20130101; H03M 1/40 20130101; H03M 1/0639 20130101; H03M
1/12 20130101; H03M 1/46 20130101; H03M 1/38 20130101; H03M 1/403
20130101; H03M 1/468 20130101 |
International
Class: |
H03M 1/06 20060101
H03M001/06; H03M 1/12 20060101 H03M001/12 |
Claims
1. A system for converting an analog signal to a digital signal,
the system comprising: a redundancy element operable to provide an
offset range; a comparator coupled to a digital-to-analog converter
(DAC), the comparator operable to compare a reference to an output
associated with the DAC; a control circuit coupled to the
redundancy element, the control circuit operable to, for a first
bit value: communicate a first conversion value to the DAC, the
first conversion value including a first offset, the first offset
associated with a first offset bit value; in response to a first
comparison result from the comparator, setting a second conversion
value; and if the first bit value has a predetermined relationship
to the first offset bit value, remove the first offset from the
second conversion value; and in response to a second comparison
result from the comparator, setting a third conversion value.
2. The system of claim 1, wherein the control circuit is further
operable to transition to a second bit value in response to the
second comparison result.
3. The system of claim 2, wherein the control circuit is further
operable to, for the second bit value: communicate a fourth
conversion value to a digital-to-analog converter (DAC), the fourth
conversion value including a first offset, the first offset
associated with a first offset bit value; in response to a third
comparison result from the comparator, setting a fifth conversion
value; and if the first bit value has a predetermined relationship
to the first offset bit value, remove the first offset from the
fifth conversion value; and in response to a fourth comparison
result from the comparator, setting a sixth conversion value.
4. The system of claim 3, wherein the control circuit is further
operable to set a seventh conversion value in response to the
second comparison result, the seventh conversion value including a
second offset, and the second offset associated with a second
offset bit value.
5. The system of claim 4, wherein the second offset is less than
the first offset.
6. The system of claim 1, wherein the DAC is a single-ended
DAC.
7. The system of claim 1, wherein the DAC is a differential
DAC.
8. The system of claim 7, wherein each of the conversion values
comprises a pair of related conversion values.
9. The system of claim 1, wherein the control circuit operates at a
fixed clock rate.
10. The system of claim 1, wherein the redundancy element is
selected from the group consisting of: a capacitor, a voltage
source, a current source, a selectable comparator offset, and an
offset control circuit.
11. The system of claim 1, wherein the redundancy element is part
of the DAC.
12. The system of claim 1, wherein the redundancy element is part
of the comparator.
13. The system of claim 1, further comprising a register coupled to
the control circuit, the register operable to temporarily store the
conversion values for access by the DAC.
14. The system of claim 7, wherein the reference is an output of
the differential DAC.
15. The system of claim 1, wherein the predetermined relationship
comprises the first bit value being one greater than the first
offset bit value.
16. A method for electronically converting an analog signal to a
digital signal, the method comprising: for a first bit value,
setting a first conversion value to include a first offset, the
first offset associated with a first offset bit value; using the
output of a first comparison, setting a second conversion value;
and if the first bit value has a predetermined relationship to the
first offset bit value, removing the first offset from the second
conversion value; and using the output of a second comparison,
setting a third conversion value, wherein setting the first
conversion value comprises charging a bottom plate of a capacitor
associated with the first bit value.
17. The method of claim 16, further comprising after using the
output of the second comparison, transitioning to a second bit
value and repeating the steps of the method for the second bit
value.
18. The method of claim 16, further comprising, prior to using the
output of the second comparison, setting a fourth conversion value
to include a second offset, the second offset associated with a
second offset bit value.
19. The method of claim 18, wherein the second offset is less than
the first offset.
20. (canceled)
Description
BACKGROUND
[0001] 1. Field
[0002] This disclosure relates generally to electrical circuitry,
and more specifically, to electrical circuitry for data
conversion.
[0003] 2. Related Art
[0004] Data converters are very useful for converting analog
signals to digital signals, and for converting digital signals to
analog signals. Many applications require data converters that have
a high resolution, fast conversion time, allow a broad range of
inputs, and yet are cost effective. Accuracy is also important to
data converters, which are susceptible to noise, settling, and
other speed and environmentally induced errors. A common technique
for eliminating these errors is redundancy, by which the data
converter can re-convert to correct errors of certain magnitude.
One of the primary benefits of redundancy in a successive
approximation data converter is to increase the conversion speed by
relaxing the DAC settling time requirements. Other data conversion
features may also be important for various applications. It is thus
important to be able to provide data converters that meet a wide
variety of potentially conflicting criteria, while at the same time
have a fast conversion time and remain cost effective
BRIEF DESCRIPTION OF THE DRAWINGS
[0005] The present disclosure is illustrated by way of example and
is not limited by the accompanying figures, in which like
references indicate similar elements. Elements in the figures are
illustrated for simplicity and clarity and have not necessarily
been drawn to scale.
[0006] FIG. 1 illustrates, in schematic form, a portion of an
analog to digital data converter in accordance with one
embodiment.
[0007] FIG. 2 illustrates, in schematic diagram form, a portion of
a single-ended digital to analog converter (DAC) of the data
converter of FIG. 1 in accordance with one embodiment.
[0008] FIG. 3 illustrates, in schematic diagram form, a portion of
a differential digital to analog converter of the data converter of
FIG. 1 in accordance with another embodiment.
[0009] FIG. 4 illustrates, in flow diagram form, a method for
adding offset to comparison bits at predetermined points in the DAC
of FIG. 2.
[0010] FIG. 5 illustrates, in flow diagram form, a method for
adding offset to comparison bits at predetermined points in the DAC
of FIG. 3.
DETAILED DESCRIPTION
[0011] A successive approximation analog to digital converter (ADC)
includes a digital to analog converter (DAC) with elements that are
added sequentially to adjust an input-dependent voltage. The
voltage is compared to a reference voltage at each addition and the
DAC elements are adjusted based on the comparison result. Upon
completion, the comparison results are a digital representation of
the analog input voltage. An offset is included in the comparison
at one or more pre-determined points. The offset is then removed
after another set of predetermined points and an extra comparison
is performed. The intentional offsets combined with the extra
comparisons create a redundancy which relaxes the requirements on
both DAC settling time and the comparator accuracy during the
portion of the approximation that uses redundancy.
[0012] FIG. 1 illustrates, in schematic form, a portion of an
analog to digital data converter 100 in accordance with one
embodiment including successive approximation register (SAR) state
machine or control circuit 102, user interface 104, SAR register
106, digital to analog converter (DAC) 108 and comparator 110. DAC
108 receives an analog input that is used to set a charge on
capacitive elements in DAC 108. Output from DAC 108 is provided to
comparator 110, which for a single-ended DAC 108 provides the
difference between a reference voltage and the output of DAC 108.
For a differential DAC 108, comparator 110 determines the
difference between a plus output of DAC 108 and a minus output of
DAC 108. The output of comparator is provided to SAR state machine
102.
[0013] User interface 104 provides control information to SAR state
machine 102 to control operating features such as operational
speed, output format, and whether to run an average of the
conversion results, among other features. SAR state machine 102 can
operate at a fixed or variable clock rate.
[0014] SAR state machine 102 controls conversion by placing
commands and parameters in SAR registers 106, which are then
provided to DAC 108. A conversion will begin when a trigger to
convert signal is sent by the SAR state machine 102. When the
asserted trigger signal is received, DAC 108 samples an input
voltage. In one embodiment, the SAR converter samples for a period
indicated by user interface 104. SAR state machine 102 then places
DAC 108 into a convert mode and provides an offset value to use
during the conversion.
[0015] In one embodiment of the convert mode, comparator 110
subsequently compares the DAC output with the intentional offset to
a reference voltage. During each comparison, SAR state machine 102
successively sets or clears the corresponding digital output bit
based on the compare result. This information gets passed into DAC
108 to adjust the DAC output by fractions of a reference voltage. A
particular offset can be used for one or more of the bits of the
DAC 108. When the bits associated with an offset have been
compared, the offset can be removed and the SAR state machine 102
can specify another offset to use for another one or more of the
bits of the DAC 108 or it can specify to remove the offset. At this
point, an extra comparison step is performed.
[0016] When the SAR converter has made the appropriate number of
successive approximations using the offsets, SAR state machine 102
indicates that it is complete and transfers the results to output
circuitry. In one embodiment, this output circuitry employs
averaging if so configured, and then formats the data in the
appropriate manner.
[0017] In some embodiments, data converter 100 may be implemented
as a semiconductor device as a single integrated circuit, may be
implemented as a plurality of integrated circuits, or may be
implemented as a combination of integrated circuits and discrete
components. Alternate embodiments may implement data converter 100
in any manner.
[0018] FIG. 2 illustrates, in schematic diagram form, a portion of
a single-ended digital to analog converter (DAC) 108 of the data
converter of FIG. 1 in accordance with one embodiment. In the
embodiment shown, DAC 108 comprises an array of binary weighted DAC
elements (e.g. capacitors) 202-216. Alternate embodiments may use
any type of charge redistribution array for data conversion in
addition to or instead of capacitors, such as a voltage source, a
current source, a selectable comparator offset, and an offset
control circuit.
[0019] In addition, alternate embodiments may use any desired and
appropriate binary weighted elements to provide conversion values
(e.g. resistive elements, capacitive elements, a combination
thereof, etc.). In the example shown, DAC elements 202-216 are
capacitors coupled in parallel to one another. DAC elements 202,
204, 206, 210, 212, 214 correspond to respective bits. DAC element
206 can be used to set an offset for DAC elements 202-204, and can
also be used if there is an overflow condition with the available
bits during the conversion process.
[0020] In the example shown, DAC element 202 corresponds to Bit
N-1, where N is the resolution of the ADC. DAC element 204
corresponds to Bit M and can be separated from DAC element 202 by
any suitable number of DAC elements. DAC element 206 can be used as
an offset during the processing of most significant Bits N-1
through M+1 and for overflow conditions, as required. DAC element
208 corresponds to Bit M-1. DAC element 210 can be separated from
DAC element 208 by any suitable number of DAC elements and
corresponds to Bit L. DAC element 212 corresponds to Bit L-1. DAC
element 214 can be separated from DAC element 212 by any suitable
number of DAC elements and corresponds to Bit 0. DAC element 216 is
a termination element that is typically not used during the
conversion. For less significant bits below Bit M, a DAC element
associated with a bit that is less significant than the bits being
converted can be used to provide an offset value. For example, if
DAC element 206 is used to provide an offset during the conversion
of Bits N-1 through Bit M+1, then DAC element 212 can be used to
provide an offset during the conversion of Bit M through Bit L.
[0021] Comparator 110 is provided with a constant reference voltage
by binary weighted DAC elements 218-224 during a conversion. DAC
elements 218-224 are shown as capacitors coupled in parallel
between a reference voltage VRL and a non-inverting input to
comparator 110.
[0022] A first terminal of a first switch 252 is coupled to the
output of DAC elements 218-224 and a non-inverting input to
comparator 110. A first terminal of a second switch 254 is coupled
to the output of DAC elements 202-216 and an inverting input to
comparator 110. A second terminal of switch 252 is coupled to a
second terminal of switch 254.
[0023] During a sample phase, switches 252 and 254 are placed in
conducting mode to short the inputs to comparator 110 to a common
mode voltage VCM. A voltage input VI is sampled onto the array of
DAC elements 202-204, 208-216. Then during an approximation phase,
switches 252 and 254 are placed in non-conducting mode and the DAC
elements 202-214 are controlled to successively approximate the
input voltage VI using the comparator 110 output to make decisions
on how to switch the DAC elements 202-214. At each step of the
approximation, the comparator 110 output is stored in the SAR
register 106 and the resulting digital word is the digital
representation of the analog input voltage VI.
[0024] A bottom plate of each DAC element 202-216 is coupled to a
respective switch array 226-240 to control the voltage applied to
DAC elements 202-216. Each switch array 226-240 includes three
switches 242-246 (as labeled for switch array 226). Switch 242 is
coupled to a low voltage VL, switch 244 is coupled to a high
voltage (VH) and switch 246 is coupled to the input voltage (VI).
During the sample phase, switch 246 is set to conducting mode to
apply the input voltage to the bottom plates of DAC elements
202-204, 208-216 and switches 242-244 are in non-conducting mode.
During the approximation phase, switch 246 is non-conducting, and
either switch 242 or 244 will be in conducting mode depending on
whether the particular bit is required to represent the input
voltage.
[0025] In the portion of DAC 108 illustrated in FIG. 2, there are
two scaling capacitors 248 and 250 that are used to reduce the
number of DAC elements 202-214 required to represent the input.
Capacitor 250 scales the voltage for DAC elements 208-216 by a
first factor of 2 (M-L). Capacitor 252 again scales the voltage for
DAC elements 212-216 by a second factor of 2 L. Although the
portion of data converter 108 illustrated in FIG. 2 has two scaling
capacitors 248, 250, alternate embodiments may have any number of
scaling capacitors. For example, by using scaling capacitors 248,
250 in a 12 bit data converter 108, only 48 DAC elements 202-204,
208-216, 218-224, 248-250 are required to represent the input
voltage plus one DAC element 206 to allow redundancy. For a
traditional 12-bit data converter, 4096 DAC elements would be
required to represent the input voltage plus additional DAC
elements to provide redundancy.
[0026] FIG. 3 illustrates, in schematic diagram form, a portion of
a differential digital to analog converter 108 of the data
converter 100 of FIG. 1 in accordance with another embodiment. In
the embodiment shown, DAC 108 comprises a first array of binary
weighted DAC elements (e.g. capacitors) 360-374 on a plus side 304
of DAC 108 and a second array of binary weighted DAC elements (e.g.
capacitors) 328-341 on a minus side 302 of DAC 108. Alternate
embodiments may use any type of charge redistribution array for
data conversion. In addition, alternate embodiments may use any
desired and appropriate binary weighted elements (e.g. resistive
elements, capacitive elements, a combination thereof, etc.). In the
example shown, DAC elements 360-374 and 328-341 are capacitors
coupled in parallel to one another. DAC elements 362-374 and
341-330 correspond to respective bits. DAC elements 338 and 370 can
be used to set an offset while performing successive approximation
using respective DAC elements 340-341 and 372-374, and can also be
used if there is an overflow condition with the available bits
during the conversion process.
[0027] In the example shown, for the minus side 302 and the plus
side 304, DAC elements 341, 374 correspond to respective Bits N-1.
DAC elements 340, 372 correspond to respective Bits M and can be
separated from corresponding DAC element 341, 374 by any suitable
number of DAC elements. DAC elements 338, 370 can be used as an
offset during the processing of most significant Bits N-1 through
M+1 and for overflow conditions in the minus side 302 and plus side
304 successive approximation results, as required. DAC elements
336, 368 correspond to respective Bits M-1. DAC elements 334, 366
can be separated from respective DAC elements 336, 368 by any
suitable number of DAC elements and correspond to respective Bits
L. DAC elements 332, 364 correspond to respective Bits L-1. DAC
elements 330, 362 can be separated from respective DAC elements
332, 364 by any suitable number of DAC elements and correspond to
Bits 0, the least significant bits. DAC elements 328, 360 are
termination elements that are typically not used during the
conversion. For less significant bits below Bits M, a DAC element
associated with a bit that is less significant than the bits being
converted can be used to provide an offset value. For example, if
DAC elements 338, 370 are used to provide an offset during the
conversion of respective Bits N-1 through Bits M+1, then DAC
elements 332, 364 can be used to provide an offset during the
conversion of respective Bits M through Bits L.
[0028] A first terminal of a first switch 380 is coupled to the
output of DAC elements 328-341 and a non-inverting input to
comparator 110. A first terminal of a second switch 382 is coupled
to the output of DAC elements 360-374 and an inverting input to
comparator 110. A second terminal of switch 380 is coupled to a
second terminal of switch 382 at a common voltage node VCM.
[0029] During a sample phase, switches 380 and 382 are placed in
conducting mode to short the inputs to comparator 110 to the common
mode voltage VCM. A plus-side input voltage VP is sampled onto the
array of DAC elements 360-368, 372-374 and a minus side input
voltage VM is sampled on the array of DAC elements 328-336,
340-341. Then during an approximation phase, switches 380 and 382
are placed in non-conducting mode and the DAC elements 362-374,
328-341 are controlled to successively approximate the plus-side
input voltage VP and minus side input voltage VM using the
comparator 110 output to make decisions on how to switch the DAC
elements 362-374 and 328-341. At each step of the approximation,
the comparator 110 output is stored in the SAR register 106 and the
resulting digital word is the digital representation of the
difference between the analog plus-side input voltage VP and minus
side input voltage VM.
[0030] A bottom plate of each DAC element 328-341, 360-374 is
coupled to a respective switch array 306-320, 344-358 to control
the voltage applied to DAC elements 328-341, 360-374. Each switch
array 306-320, 344-358 includes three respective switches 390-394,
384-388 (as labeled for switch arrays 320 and 358). Switches 392,
388 are coupled to a low voltage VL, switches 394, 386 are coupled
to a high voltage (VH) and switches 390, 384 are coupled to the
minus-side input voltage VM and plus-side input voltage VP,
respectively. During the sample phase, switches 390, 384 are set to
conducting mode to apply the input voltage to the bottom plates of
DAC elements 328-336, 340-341, 360-368, 372-374 and switches
392-394, 386-388 are in non-conducting mode. During the
approximation phase, switches 390, 384 are non-conducting, and
either switches 392 or 394, and 388 or 386 will be in conducting
mode depending on whether the particular bit is required to
represent the respective differential input voltage.
[0031] In the portion of DAC 108 illustrated in FIG. 3, scaling
capacitors 342-343 and 376-378 are used to reduce the number of DAC
elements 328-341, 362-374 required to represent the input voltages.
Capacitors 343 and 378 scale the voltages for respective DAC
elements 328-346, 360-368 by a first factor of 2 (M-L). Capacitors
342, 376 again scale the voltages for respective DAC elements
328-332 and 360-364 by a second factor of 2 L. Although the portion
of data converter 108 illustrated in FIG. 3 has four scaling
capacitors 342, 343, 376, 378, alternate embodiments may have any
number of scaling capacitors. For example, by using scaling
capacitors 342, 343, 376, 378 in a 12 bit data converter 108, only
ninety-six DAC elements 328-336, 340-343, 360-368, 372-378 are
required to represent the differential input voltage plus two DAC
elements 338, 370 to allow redundancy. For a traditional 12-bit
differential data converter, 8192 DAC elements would be required to
represent the differential input voltage plus additional DAC
elements to allow redundancy.
[0032] Referring to FIGS. 2 and 4, FIG. 4 illustrates, in flow
diagram form, a method 400 for adding offset to comparison bits at
predetermined points in the DAC 108 of FIG. 2. Process 402 includes
initializing an offset value to a first value for the approximation
phase using a predetermined set of DAC elements, where capacitors
are used for the DAC elements. For example, for DAC elements
202-206 in FIG. 2, DAC element 208 can be used to create an offset
that is one-half the value of the lowest bit weight in the group of
DAC elements 202-204. If DAC 108 is a 12-bit DAC with little endian
architecture, and DAC element 204 corresponds to Bit 8 (with DAC
element 202 corresponding to Bit 11), the weight of DAC element 204
would be 256 and DAC element 208 could be used to provide an offset
value of 128 while DAC elements 202-206 are being converted. Other
suitable offset values can be used.
[0033] Process 404 includes charging the bottom plates of
capacitors for selected DAC elements. DAC elements are added in one
by one during the approximation phase. For example, DAC element 202
is initially selected, and then DAC element 204 (assuming no
intervening DAC elements between DAC elements 202 and 204), and
then DAC element 206, and so on. DAC element 208 can be used to
provide an offset while DAC elements 202-206 are being selected for
successive approximation.
[0034] Process 406 includes using comparator 110 to determine
whether the output of the selected DAC elements is greater than the
reference voltage. If so, process 408 includes discharging the
bottom plate of the capacitor corresponding to the bit most
recently added to or included in the approximation. If the output
value of the selected DAC elements is less than or equal to the
reference voltage, process 410 retains the most recently added bit
in the approximation. That is, the bottom plate of the
corresponding capacitor is not discharged.
[0035] After performing process 408 or 410, process 412 determines
whether the most recently added bit (whether retained in the
approximation or not) has a predetermined relationship to the bit
or DAC element being used to add the offset, referred to as the
redundant bit. For example, in some embodiments, if the bit used
for the offset is directly after the most recently added bit, then
the bit used for the offset meets the criteria for having a
predetermined relationship to the most recently added bit and
process 412 transitions to process 414 to remove the offset from
the output of the DAC elements.
[0036] After process 414, process 416 reduces the offset value to a
next lower predetermined value. For example, for the DAC 108 shown
in FIG. 2, Bit 4 may be used to supply an offset during the
successive approximation on Bits 5-7, and the value of the next
offset can be set to a value that is one-half the value of the
lowest bit weight in the group of Bits 5-7. For a 12-bit DAC, the
weight of Bit 5 would be 32 and the value of the offset would be
16. Other suitable values can be used for the offset, however.
After process 416, process 418 adds the new offset value to the DAC
output. If the path of processes 414-418 was chosen, there is no
transition to the next bit and the same bit value is used for the
next sequence of method 400.
[0037] Referring again to process 412, if the most recently added
bit does not have a predetermined relationship to the redundant
bit, process 420 transitions to the next bit, if any, in order.
After process 418 or 420 are executed, process 422 determines
whether the last bit in the DAC word has been previously selected,
that is, if the next bit is beyond the number of bits included in
the DAC word. If so, process 422 ends method 400. If not, process
422 transitions back to process 404.
[0038] Referring to FIGS. 2 and 5, FIG. 5 illustrates, in flow
diagram form, a method 500 for adding offset to comparison bits at
predetermined points in the differential DAC 108 of FIG. 3. Process
502 includes initializing offset values for plus and minus branches
304, 302 to first values for the approximation phase using a
predetermined set of DAC elements, where capacitors are used for
the DAC elements. For example, for DAC elements 338-341, 370-374 in
FIG. 3, respective DAC elements 314, 368 can be initialized to a
value that is one-half the value of the lowest bit weight in the
group of DAC elements 338-341, 370-374. If DAC 108 is a 12-bit DAC
with little endian architecture, and DAC elements 314, 368
correspond to Bit 7 (with DAC elements 341, 374 corresponding to
Bit 11), the weight of DAC elements 314, 368 would be 128 and DAC
elements 314, 368 could be used to provide an offset value of 128
during the portion of the approximation that uses DAC elements
338-341, 370-374. Other suitable offset values can be used.
[0039] Process 504 includes charging the bottom plates of
capacitors for selected bits or DAC elements. DAC elements are
added in one by one during the approximation phase. For example,
DAC elements 341, 374 are initially selected, and then DAC elements
340 and 372, (assuming no intervening DAC elements between DAC
elements 341 and 340, and between DAC elements 374 and 372), and
then DAC element 338 (minus side 302) and DAC element 370 (plus
side 304), and so on. DAC elements 336, 368 can be used to provide
respective offsets.
[0040] Process 506 includes using comparator 110 to determine
whether the output of the selected DAC elements on the plus side
304 is greater than the DAC output on the minus side 302. If so,
process 508 includes discharging the bottom plate of the capacitor
corresponding to the bit most recently added to or included in the
approximation on the plus side 304 and retaining the most recently
bit in the minus side 302. If the output of the selected DAC
elements on the plus side 304 is less than or equal to the DAC
output on the minus side 302, process 510 includes discharging the
bottom plate of the capacitor corresponding to the bit most
recently added to or included in the approximation on the minus
side 302 and retaining the most recently bit in the plus side
304.
[0041] After performing process 508 or 510, process 512 determines
whether the most recently added bit (whether retained in the
approximation or not) has a predetermined relationship to the bit
or DAC element being used to add the offset, referred to as the
redundant bit. For example, in some embodiments, if the bit used
for the offset is directly after the most recently added bit, then
the bit used for the offset meets the criteria for having a
predetermined relationship to the most recently added bit and
process 512 transitions to process 514 to remove the offset from
the output of the DAC elements on the plus side 304 and the minus
side 302.
[0042] After process 514, process 516 reduces the offset value to a
next lower predetermined value. For example, for the DAC 108 shown
in FIG. 3, Bit 4 may be used to supply an offset during the
successive approximation on Bits 5-7, and the value of the next
offset can be set to a value that is one-half the value of the
lowest bit weight in the group of Bits 5-7. For a 12-bit DAC, the
weight of Bit 5 would be 32 and the value of the offset would be
16. Other suitable values can be used for the offset, however.
After process 516, process 518 adds the new offset value to the DAC
output. If the path of processes 514-518 was chosen, there is no
transition to the next bit since the same bit value is used for the
next sequence of method 500.
[0043] Referring again to process 512, if the most recently added
bit does not have a predetermined relationship to the redundant
bit, process 520 transitions to the next bit, if any, in order.
After process 518 or 520 are executed, process 522 determines
whether the last bit in the DAC word has been previously selected,
that is, if the next bit is beyond the number of bits included in
the DAC word. If so, process 522 ends method 500. If not, process
522 transitions back to process 504.
[0044] By now it should be appreciated that there has been provided
a data converter 100 that uses existing components to provide
redundancy and improve accuracy while speeding up operation. Errors
are corrected during a DAC approximation phase without requiring
complicated result translations, ROM arrays, or lookup tables and
without altering a standard binary DAC structure beyond having one
additional element to handle overflow.
[0045] In some embodiments, a system for converting an analog
signal to a digital signal can comprise a redundancy element [370]
operable to provide an offset range, and a comparator [110] coupled
to a digital-to-analog converter (DAC). The comparator is operable
to compare a reference to an output associated with the DAC. A
control circuit
[0046] is coupled to the redundancy element and is operable to, for
a first bit value, communicate a first conversion value to the DAC
[108] including a first offset [404] associated with a first offset
bit value [402]. In response to a first comparison result [406]
from the comparator, a second conversion value [408, 410] is set.
If the first bit value has a predetermined relationship to the
first offset bit value [412], the first offset is removed from the
second conversion value [414]. In response to a second comparison
result [406, second time] from the comparator, a third conversion
value [408, 410, second time] is set.
[0047] In another aspect, the control circuit can be further
operable to transition to a second bit value [420] in response to
the second comparison result.
[0048] In another aspect, the control circuit can be further
operable to, for the second bit value, communicate a fourth
conversion value to a digital-to-analog converter (DAC) [108]. The
fourth conversion value can include a first offset [404], the first
offset associated with a first offset bit value [402]. In response
to a third comparison result [406] from the comparator, a fifth
conversion value [408, 410] can be set. If the first bit value has
a predetermined relationship to the first offset bit value [412],
the first offset can be removed from the fifth conversion value
[414]. In response to a fourth comparison result [406, second time]
from the comparator, a sixth conversion value [408, 410, second
time] can be set.
[0049] In another aspect, the control circuit can be further
operable to set a seventh conversion value [418] in response to the
second comparison result. The seventh conversion value can include
a second offset [416], and the second offset can be associated with
a second offset bit value.
[0050] In another aspect, the second offset can be less than the
first offset.
[0051] In another aspect, the can be is a single-ended DAC [FIG.
2].
[0052] In another aspect, the DAC can be a differential DAC [FIG.
3].
[0053] In another aspect, each of the conversion values can
comprise a pair of related conversion values [FIGS. 3, 5].
[0054] In another aspect, the control circuit can operate at a
fixed clock rate.
[0055] In another aspect, the redundancy element can be selected
from the group consisting of: a capacitor, a voltage source, a
current source, a selectable comparator offset, and an offset
control circuit.
[0056] In another aspect, the redundancy element can be part of the
DAC.
[0057] In another aspect, the redundancy element can be part of the
comparator.
[0058] In another aspect, the system can further comprise a
register [106] coupled to the control circuit. The register can be
operable to temporarily store the conversion values for access by
the DAC.
[0059] In another aspect, the reference can be an output of the
differential DAC.
[0060] In another aspect, the predetermined relationship can
comprise the first bit value being one greater than the first
offset bit value.
[0061] In other embodiments, a method for electronically converting
an analog signal to a digital signal can comprise, for a first bit
value, setting a first conversion value [404] to include a first
offset [402], the first offset associated with a first offset bit
value and using the output of a first comparison [406], setting a
second conversion value [408, 410]. If the first bit value has a
predetermined relationship to the first offset bit value [412], the
first offset can be removed from the second conversion value [414].
The output of a second comparison [406, second time] can be used to
set a third conversion value [408, 410, second time].
[0062] In another aspect, the method can further comprise, after
using the output of the second comparison, transitioning to a
second bit value [420] and repeating the steps of the method for
the second bit value.
[0063] In another aspect, the method can further comprise, prior to
using the output of the second comparison, setting a fourth
conversion value [418] to include a second offset
[0064] , the second offset associated with a second offset bit
value.
[0065] In another aspect, the second offset can be less than the
first offset.
[0066] In another aspect, setting the first conversion value can
comprises charging a bottom plate of a capacitor associated with
the first bit value.
[0067] Because the apparatus implementing the present disclosure
is, for the most part, composed of electronic components and
circuits known to those skilled in the art, circuit details will
not be explained in any greater extent than that considered
necessary as illustrated above, for the understanding and
appreciation of the underlying concepts of the present disclosure
and in order not to obfuscate or distract from the teachings of the
present disclosure.
[0068] Some of the above embodiments, as applicable, may be
implemented using a variety of different information processing
systems. Those skilled in the art will recognize that the
boundaries between logic blocks are merely illustrative and that
alternative embodiments may merge logic blocks or circuit elements
or impose an alternate decomposition of functionality upon various
logic blocks or circuit elements.
[0069] Thus, it is to be understood that the architectures depicted
herein are merely exemplary, and that in fact many other
architectures can be implemented which achieve the same
functionality. In an abstract, but still definite sense, any
arrangement of components to achieve the same functionality is
effectively "associated" such that the desired functionality is
achieved. Hence, any two components herein combined to achieve a
particular functionality can be seen as "associated with" each
other such that the desired functionality is achieved, irrespective
of architectures or intermediate components. Likewise, any two
components so associated can also be viewed as being "operably
connected," or "operably coupled," to each other to achieve the
desired functionality.
[0070] Furthermore, those skilled in the art will recognize that
boundaries between the functionality of the above described
operations are merely illustrative. The functionality of multiple
operations may be combined into a single operation, and/or the
functionality of a single operation may be distributed in
additional operations. Moreover, alternative embodiments may
include multiple instances of a particular operation, and the order
of operations may be altered in various other embodiments.
[0071] Although the disclosure is described herein with reference
to specific embodiments, various modifications and changes can be
made without departing from the scope of the present disclosure as
set forth in the claims below. For example, any one or more of the
features described herein may be used in any desired and
appropriate combination with any other features. Accordingly, the
specification and figures are to be regarded in an illustrative
rather than a restrictive sense, and all such modifications are
intended to be included within the scope of the present disclosure.
Any benefits, advantages, or solutions to problems that are
described herein with regard to specific embodiments are not
intended to be construed as a critical, required, or essential
feature or element of any or all the claims.
[0072] The term "coupled," as used herein, is not intended to be
limited to a direct coupling or a mechanical coupling.
[0073] Furthermore, the terms "a" or "an," as used herein, are
defined as one or more than one. Also, the use of introductory
phrases such as "at least one" and "one or more" in the claims
should not be construed to imply that the introduction of another
claim element by the indefinite articles "a" or "an" limits any
particular claim containing such introduced claim element to
disclosures containing only one such element, even when the same
claim includes the introductory phrases "one or more" or "at least
one" and indefinite articles such as "a" or "an." The same holds
true for the use of definite articles.
[0074] Unless stated otherwise, terms such as "first" and "second"
are used to arbitrarily distinguish between the elements such terms
describe. Thus, these terms are not necessarily intended to
indicate temporal or other prioritization of such elements.
* * * * *