U.S. patent application number 10/803128 was filed with the patent office on 2005-10-06 for method and apparatus for reducing noise in analog-to-digital converter devices.
Invention is credited to Bright, William J., Corsi, Marco, Kinyua, Martin Kithinji, Smith, William David.
Application Number | 20050219106 10/803128 |
Document ID | / |
Family ID | 35053683 |
Filed Date | 2005-10-06 |
United States Patent
Application |
20050219106 |
Kind Code |
A1 |
Corsi, Marco ; et
al. |
October 6, 2005 |
METHOD AND APPARATUS FOR REDUCING NOISE IN ANALOG-TO-DIGITAL
CONVERTER DEVICES
Abstract
An analog-to-digital converter apparatus has a plurality of
stages. Each stage includes a residue amplifier having a first and
second amplifier unit. Each of the amplifier units has a first
input locus, a second input locus and an output locus. The
amplifier units cooperate in receiving a differential input data
signal at the first input loci. A DC level setting signal unit is
coupled with the second input loci and provides a DC level setting
current in a first current direction. A counter-current signal
generating unit is coupled with the second input loci via a single
coupling locus common with the second input loci and provides a
control current signal to the second input loci in a second current
direction opposite to the first current direction. The control
current signal provides a DC level control for each of the
amplifier units.
Inventors: |
Corsi, Marco; (Parker,
TX) ; Bright, William J.; (Dallas, TX) ;
Kinyua, Martin Kithinji; (Dallas, TX) ; Smith,
William David; (Allen, TX) |
Correspondence
Address: |
TEXAS INSTRUMENTS INCORPORATED
P O BOX 655474, M/S 3999
DALLAS
TX
75265
|
Family ID: |
35053683 |
Appl. No.: |
10/803128 |
Filed: |
March 17, 2004 |
Current U.S.
Class: |
341/161 |
Current CPC
Class: |
H03M 1/447 20130101;
H03M 1/08 20130101 |
Class at
Publication: |
341/161 |
International
Class: |
H03M 001/38 |
Claims
1. A current mode pipeline analog-to-digital converter apparatus
including a plurality of stages; each respective stage of said
plurality of stages comprising: (a) a respective residue amplifier
including a first amplifying unit and a second amplifying unit;
each of said first and second amplifying units having an inverting
input locus, a non-inverting input locus and an output locus; each
of said first and second amplifying units receiving a differential
input data signal at one input locus of said inverting input locus
and said non-inverting input locus; the other input loci of said
first and second amplifying units other than said one input locus
receiving a first current signal in a first current direction
providing a DC level setting signal for each of said first and
second amplifying units; signals presented at said output loci
substantially representing said input data signal less said DC
level setting signal; and (b) a counter-current signal generating
unit coupled with said other input loci at a single coupling locus;
said counter-current signal generating unit presenting a second
current signal in a second current direction opposite to said first
current direction providing a DC level control signal for each of
said first and second amplifying units.
2. A current mode pipeline analog-to-digital converter apparatus
including a plurality of stages as recited in claim 1 wherein said
first current signal is provided by an NPN digital-to-analog
converter unit.
3. A current mode pipeline analog-to-digital converter apparatus
including a plurality of stages as recited in claim 1 wherein said
counter-current signal generating unit is a PNP digital-to-analog
converter unit
4. A current mode pipeline analog-to-digital converter apparatus
including a plurality of stages as recited in claim 2 wherein said
counter-current signal generating unit is a PNP digital-to-analog
converter unit.
5. An analog-to-digital converter apparatus having a plurality of
stages; each respective stage of said plurality of stages
comprising: (a) a residue amplifier having a first amplifier unit
and a second amplifier unit; each of said first amplifier unit and
said second amplifier unit having a first input locus, a second
input locus and an output locus; said first and second amplifier
units cooperating in receiving a differential input data signal at
said first input loci of said first and second amplifier units; (b)
a DC level setting signal unit coupled with said second input loci
of said first and second amplifier units; said DC level setting
signal unit providing a DC level setting current in a first current
direction to said second input loci; and (c) a counter-current
signal generating unit coupled with said second input loci via a
single coupling locus common with said second input loci; said
counter-current signal generating unit providing a control current
signal to said second input loci in a second current direction
opposite to said first current direction; said control current
signal providing a DC level control for each of said first and
second amplifier units.
6. An analog-to-digital converter apparatus having a plurality of
stages as recited in claim 5 wherein said DC level setting current
unit is an NPN digital-to-analog converter unit.
7. An analog-to-digital converter apparatus having a plurality of
stages as recited in claim 5 wherein said counter-current signal
generating unit is a PNP digital-to-analog converter unit.
8. An analog-to-digital converter apparatus having a plurality of
stages as recited in claim 6 wherein said counter-current signal
generating unit is a PNP digital-to-analog converter unit.
9. A method for reducing noise in input signals to a residue
amplifier in an analog-to-digital converter apparatus; the residue
amplifier having a first amplifier unit and a second amplifier
unit; each of said first amplifier unit and said second amplifier
unit having a first input locus, a second input locus and an output
locus; said first and second amplifier units cooperating in
receiving a differential input data signal at said first input loci
of said first and second amplifier units; a DC level setting signal
unit coupled with said second input loci of said first and second
amplifier units provides a DC level setting current in a first
current direction to said second input loci; the method comprising
the steps of: (a) providing a counter-current signal generating
unit coupled with said second input loci via a single coupling
locus common with said second input loci; and (b) operating said
countercurrent signal generating unit to provide a control current
signal to said second input loci in a second current direction
opposite to said first current direction to establish a DC level
control for each of said first and second amplifier units.
10. A method for reducing noise in input signals to a residue
amplifier in an analog-to-digital converter apparatus as recited in
claim 9 wherein said DC level setting unit Is an NPN
digital-to-analog converter unit.
11. A method for reducing noise in input signals to a residue
amplifier in an analog-to-digital converter apparatus as recited in
claim 9 wherein said counter-current signal generating unit is a
PNP digital-to-analog converter unit.
12. A method for reducing noise in input signals to a residue
amplifier in an analog-to-digital converter apparatus as recited in
claim 10 wherein said counter-current signal generating unit is a
PNP digital-to-analog converter unit.
Description
BACKGROUND OF THE INVENTION
[0001] The present invention is directed to analog-to-digital
converter apparatuses, and especially to current mode pipeline
analog-to-digital converter apparatuses that include residue
amplifiers in a plurality of stages.
[0002] A current mode pipeline analog-to-digital converter (ADC)
usually employs a plurality of stages, each stage including a
residue amplifier operating in cooperation with a track-and-hold
device. In its preferred embodiment, the residue amplifier receives
a differential analog signal at two amplifier units. A DC (direct
current) level setting current signal is also provided to the two
amplifier units to set the DC levels, and ultimately to set the
common mode voltage for the two amplifier units. A preferred source
for such DC level setting current signals is an NPN
digital-to-analog converter (DAC). When an NPN DAC is used to
provide DC level setting currents in a current mode pipeline ADC,
it has been found useful to employ a PNP DAC to provide a control
current signal to the two amplifier units to recentralize the
common mode voltage of the output of the residue amplifier.
[0003] In configurations employing both a PNP DAC and an NPN DAC,
both DAC devices are first order noise sources contributing noise
that can be manifested in the output of a residue amplifier.
[0004] Noise is always a concern for designers of electronic
devices, including ADC devices. It is desirable that noise in the
output of the residue amplifier devices in an ADC apparatus be
minimized in so far as can be achieved while retaining other
advantageous operational characteristics.
SUMMARY OF THE INVENTION
[0005] An analog-to-digital converter apparatus has a plurality of
stages. Each stage includes a residue amplifier having a first and
second amplifier unit. Each of the amplifier units has a first
input locus, a second input locus and an output locus. The
amplifier units cooperate in receiving a differential input data
signal at the first input loci. A DC level setting signal unit is
coupled with the second input loci and provides a DC level setting
current in a first current direction. A counter-current signal
generating unit is coupled with the second input loci via a single
coupling locus common with the second input loci and provides a
control current signal to the second input loci in a second current
direction opposite to the first current direction. The control
current signal provides a DC level control for each of the
amplifier units.
[0006] It is, therefore, an object of the present invention to
reduce noise in the output of a residue amplifier device in an ADC
apparatus.
[0007] Further objects and features of the present invention will
be apparent from the following specification and claims when
considered in connection with the accompanying drawings, in which
like elements are labeled using like reference numerals in the
various figures, illustrating the preferred embodiments of the
invention.
BRIEF DESCRIPTION OF THE DRAWINGS
[0008] FIG. 1 is an electrical schematic diagram illustrating a
prior art analog-to-digital converter apparatus.
[0009] FIG. 2 is an electrical schematic diagram illustrating an
analog-to-digital converter apparatus configured according to the
present invention.
[0010] FIG. 3 is a flow diagram illustrating the method of the
present invention.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
[0011] FIG. 1 is an electrical schematic diagram illustrating a
prior art analog-to-digital converter apparatus. In FIG. 1, an
analog-to-digital converter (ADC) apparatus stage 10 includes a
residue amplifier 12, an NPN digital-to-analog converter (DAC) 14
and a PNP DAC 16. NPN DAC 14 is embodied in a plurality of NPN DACs
(indicated by dotted line 15); there are preferably 2.sup.n NPN
DACs 14 for each n bits handled by an analog-to-digital apparatus
(not shown in FIG. 1) incorporating ADC apparatus stage 10.
[0012] Residue amplifier 12 includes a first amplifier unit 20
having a first input locus 22, a second input locus 24 and an
output locus 26. A feedback network including a resistor 28
connects output locus 26 with second input locus 24. In the
embodiment of ADC apparatus stage 10 illustrated in FIG. 1, first
input locus 22 is a non-inverting input locus and second input
locus 24 is an inverting input locus. Residue amplifier 12 also
includes a second amplifier unit 30 having a first input locus 32,
a second input locus 34 and an output locus 36. A feedback network
including a resistor 38 connects output locus 36 with second input
locus 34. In the embodiment of ADC apparatus stage 10 illustrated
in FIG. 1, first input locus 32 is a non-inverting input locus and
second input locus 34 is an inverting input locus. Second input
loci 24, 34 are connected by an additional network including
resistors 40, 42 coupled in series.
[0013] NPN DAC 14 includes a first NPN bipolar transistor 50 having
a collector 52, an emitter 54 and a base 56. NPN DAC 14 also
includes a second NPN bipolar transistor 60 having a collector 62,
an emitter 64 and a base 66. A current source 58 is coupled between
emitters 54, 64 and ground 69. Collector 52 is coupled with second
input locus 24 of first amplifier unit 20 and base 56 is at a
potential (not shown in detail in FIG. 1) to effect cooperation
between transistor 50 and current source 58 to apply a current
I.sub.np to second input locus 24. Collector 62 is coupled with
second input locus 34 of second amplifier unit 30 and base 66 is at
a potential (not shown in detail in FIG. 1) to effect cooperation
between transistor 60 and current source 58 to apply current Inn to
second input locus 34. Bases 56, 66 (and associated bases in
additional NPN DACs; not shown in FIG. 1) receive digital control
signals that are determined by input levels in previous stages of
an analog-to-digital apparatus (not shown in FIG. 1) incorporating
ADC apparatus stage 10.
[0014] PNP DAC 16 includes a first bipolar PNP transistor 70 having
a collector 72, an emitter 74 and a base 76. NPN DAC 14 also
includes a second PNP bipolar transistor 80 having a collector 82,
an emitter 84 and a base 86. Emitters 74, 84 are coupled with a
voltage supply locus 89 for receiving a supply voltage V.sub.CC.
Collector 72 is coupled with second input locus 24 of first
amplifier unit 20 and base 76 is at a potential (not shown in
detail in FIG. 1) to effect cooperation between transistor 70 and
supply voltage V.sub.CC to apply a current I.sub.pn to second input
locus 24. Collector 82 is coupled with second input locus 34 of
second amplifier unit 30 and base 86 is at a potential (not shown
in detail in FIG. 1) to effect cooperation between transistor 80
and supply voltage V.sub.CC to apply current I.sub.pp to second
input locus 34.
[0015] Currents I.sub.nn, I.sub.np participate in establishing a DC
(direct current) level for operation of residue amplifier 12.
Signals presented at output loci 26, 36 substantially represent
said input data signals received at input loci 22, 32 less the DC
level established by signals appearing at second input loci 24, 34.
The other participants in establishing DC current level for
operation of residue amplifier 12 are currents I.sub.pn, I.sub.pp
from PNP DAC 16. Currents I.sub.pn, I.sub.pp are provided to
recentralize common mode voltage for output signals appearing at
output loci 26, 36.
[0016] NPN DAC 14 and PNP DAC 16 are each first order noise
sources. Each of currents I.sub.pn, I.sub.pp, I.sub.nn, I.sub.np
contributes noise to residue amplifier 12. Current I.sub.pn
contributes a noise current I.sub.pn(noise). Current I.sub.pp
contributes a noise current I.sub.pp(noise). Current I.sub.nn
contributes a noise current I.sub.nn(noise). Current I.sub.np
contributes a noise current I.sub.np(noise). Thus, noise N is
contributed to input loci 24, 34 by both NPN DAC 14 and PNP DAC 16,
and noise appearing at output loci 26, 36 is related to noise
currents I.sub.pn(noise), I.sub.pp(noise), I.sub.nn(noise),
I.sub.np(noise): 1 N I pn ( noise ) 2 + I pp ( noise ) 2 + I nn (
noise ) 2 + I np ( noise ) 2 [ 1 ]
[0017] Where, .about. indicates "related to".
[0018] Among other things, noise is a source of distortion in a
circuit, and its removal is desirable so long as operation of the
circuit is not degraded. The present invention removes the noise
contributed to input loci 24, 34 by PNP DAC 16 by providing a
single current source connected to a single coupling locus for both
amplifier units 20, 30. Preferably, the coupling locus is situated
between resistors 40, 42.
[0019] FIG. 2 is an electrical schematic diagram illustrating an
analog-to-digital converter apparatus configured according to the
present invention. In FIG. 2, an analog-to-digital converter (ADC)
apparatus stage 110 includes a residue amplifier 112, an NPN
digital-to-analog converter (DAC) 114 and a PNP DAC 116. NPN DAC
114 is embodied in a plurality of NPN DACs (indicated by dotted
line 115); there are preferably 2.sup.n NPN DACs 114 for each n
bits handled by an analog-to-digital apparatus (not shown in FIG.
2) incorporating ADC apparatus stage 110.
[0020] Residue amplifier 112 includes a first amplifier unit 120
having a first input locus 122, a second input locus 124 and an
output locus 126. A feedback network including a resistor 128
connects output locus 126 with second input locus 124. In the
embodiment of ADC apparatus stage 110 illustrated in FIG. 2, first
input locus 122 is a non-inverting input locus and second input
locus 124 is an inverting input locus. Residue amplifier 112 also
includes a second amplifier unit 130 having a first input locus
132, a second input locus 134 and an output locus 136. A feedback
network including a resistor 138 connects output locus 136 with
second input locus 134. In the embodiment of ADC apparatus stage
110 illustrated in FIG. 2, first input locus 132 is a non-inverting
input locus and second input locus 134 is an inverting input locus.
Second input loci 124, 134 are connected by an additional network
including resistors 140, 142 coupled in series.
[0021] NPN DAC 114 includes a first NPN bipolar transistor 150
having a collector 152, an emitter 154 and a base 156. NPN DAC 114
also includes a second NPN bipolar transistor 160 having a
collector 162, an emitter 164 and a base 166. A current source 158
is coupled between emitters 154, 164 and ground 169. Collector 152
is coupled with second input locus 124 of first amplifier unit 120
and base 156 is at a potential (not shown in detail in FIG. 2) to
effect cooperation between transistor 150 and current source 158 to
apply a current I.sub.np to second input locus 124. Collector 162
is coupled with second input locus 134 of second amplifier unit 130
and base 166 is at a potential (not shown in detail in FIG. 2) to
effect cooperation between transistor 160 and current source 158 to
apply current I.sub.nn to second input locus 134. Bases 156, 166
(and associated bases in additional NPN DACs; not shown in FIG. 2)
receive digital control signals that are determined by input levels
in previous stages of an analog-to-digital apparatus (not shown in
FIG. 2) incorporating ADC apparatus stage 110.
[0022] PNP DAC 116 includes a first bipolar PNP transistor 170
having a collector 172, an emitter 174 and a base 176. NPN DAC 114
also includes a second PNP bipolar transistor 180 having a
collector 182, an emitter 184 and a base 186. Emitters 174, 184 are
coupled with a voltage supply locus 189 for receiving a supply
voltage V.sub.CC. Collectors 172, 182 are coupled with a coupling
locus 141. Base 176 is at a potential (not shown in detail in FIG.
2) to effect cooperation between transistor 170 and supply voltage
V.sub.CC to apply a current I.sub.pn to coupling locus 141. Base
186 is at a potential (not shown in detail in FIG. 2) to effect
cooperation between transistor 180 and supply voltage V.sub.CC to
apply a current I.sub.pp to coupling locus 141. Thus, PNP DAC 116
provides a total current I.sub.P that is equal to
(I.sub.pn+I.sub.pp) to coupling locus 141. Current 2 I P 2
[0023] is thereby applied to input locus 124 (via resistor 140),
and current 3 I P 2
[0024] is thereby applied to input locus 134 (via resistor 142).
Resistors 140, 142 are substantially equal in value. Currents
I.sub.pp, I.sub.pn flow in an opposing direction to current flow of
currents I.sub.np, I.sub.nn that are applied to input loci 124, 134
from collectors 152, 162.
[0025] Currents I.sub.nn, I.sub.np participate in establishing a DC
(direct current) level for operation of residue amplifier 112.
Signals presented at output loci 126, 136 substantially represent
said input data signals received at input loci 122, 132 less the DC
level established by signals appearing at second input loci 124,
134. The other participants in establishing DC current level for
operation of residue amplifier 112 are currents I.sub.pn, I.sub.pp
(provided as current I.sub.p) from PNP DAC 116. Currents I.sub.pn,
I.sub.pp are provided to recentralize common mode voltage for
output signals appearing at output loci 126, 136. By applying
currents I.sub.pn, I.sub.pp to input loci 124, 134 from single
coupling locus 141, currents I.sub.pn, I.sub.pp do not contribute
to noise at input loci 124, 134. The first order noise from PNP DAC
116 is eliminated from operation of residue amplifier 112 without
degrading operation of residue amplifier 112.
[0026] FIG. 3 is a flow diagram illustrating the method of the
present invention. In FIG. 3, a method 200 for reducing noise in
input signals to a residue amplifier in an analog-to-digital
converter apparatus begins at a START locus 210. The residue
amplifier has a first amplifier unit and a second amplifier unit.
Each of the first amplifier unit and the second amplifier unit has
a first input locus, a second input locus and an output locus. The
first and second amplifier units cooperate in receiving a
differential input data signal at the first input loci of the first
and second amplifier units. A DC level setting signal unit coupled
with the second input loci of the first and second amplifier units
provides a DC level setting current in a first current direction to
the second input loci.
[0027] Method 200 continues with the step of providing a
counter-current signal generating unit coupled with the second
input loci via a single coupling locus common with the second input
loci, as indicated by a block 212. Method 200 continues with the
step of operating the counter-current signal generating unit to
provide a control current signal to the second input loci in a
second current direction opposite to the first current direction to
establish a DC level control for each of the first and second
amplifier units, as indicated by a block 214. Method 200 terminates
at an END locus 216.
[0028] It is to be understood that, while the detailed drawings and
specific examples given describe preferred embodiments of the
invention, they are for the purpose of illustration only, that the
apparatus and method of the invention are not limited to the
precise details and conditions disclosed and that various changes
may be made therein without departing from the spirit of the
invention which is defined by the following claims:
* * * * *