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AD522AD-AD522BD
High Accuracy Data Acquisition Instrumentation Amplifier
ANALOG
DEVICES
High Accuracy Data Acquisition
_l!1t,tyiI1tt1.tatle, Amplifier
FEATURES
Performance
Low Drift: 2.0uV/°C (ADSZZB)
Low Nonlinearity: 0.005% (G _ 1001
High CMRR: >110dB (G = 1000)
Low Noise: 1.5pV p-p (0.1 to 100Hz)
Low Initial Vos: 100pV (AD522B)
V_ersatilig_
Single-Resistor Gain Programmable: 1 'C, G s;
Output Reference and Sense Terminals
Data Guard for improving ac CMR
Internally Compensated
No External Components except Gain Resistor
Active Trimmed Offset, Gain, and CMR
PRODUCT DESCRIPTION
The AD522 is a precision IC instrumentation amplifier designed
for data acquisition applications requiring high accuracy
under worst-case operating conditions. An outstanding com-
bination of high linearity, high common mode rejection, low
voltage drift, and low noise makes the A0522 suitable for
use in many 12-bit data acquisition systems.
An instrumentation amplifier is usually employed as a bridge
amplifier for resistance transducers (thermistors, strain gauges,
etc.) found in process control, instrumentation, data processing,
and medical testing. The operating environment is frequently
characterized by low signal-to-noise levels, fluctuating tempera-
tures, unbalanced input impedanccs, and rcmolc location which
hinders recalibration.
The AD522 was designed to provide highly accurate signal con-
ditioning under these severe conditions. It provides output off-
sct voltage drift of less than 1opV/"C, input offset voltage drift
of less than 2, 0pV/0C, CMR above 80dB at unity gain (110dB
at G = 1000), maximum gain nonlinearity of 0. 001% at G-- - l,
and typical Input impedance of 1099..
This excellent performance [S achieved by combining a proven
circuit configuration with state-of-the-art manufacturing tech-
nology which utilizes active laser trimming of tighetolerance
thin-film resistors to achieve low cost, small size and high relia-
bility. This combination of high value with no-compromise per-
formance gives the ADS 22 thc bust features of both mono-
lithic and modular instrumentation amplifiers, thus providing
extremely cost-effective precision low-level amplification.
The AD522 is available in three versions with differing accu-
racies and operating ttrmperaturc" ranges; the 'A',' and "R"
are specified from -25''c to +85°C, and the "S'' is guaran-
lnlormahon furnished by Analog Dev,ces Is believed Io be accurate
and reliable However, no responsiblity I: assumed by Analog Devices
fur I15 use, nor for any irMrin9ements ot patents or other nghts oi third
parties wmch may result from ‘Its use, No Incense IS granted by ImnIICB'
I10" or otherwise under any patenl or patent rights of Analog Deuces
teed over the military/aerospace temperature range of -55''C
to +125°C. All versions are packaged in a 14-pin DIP and are
supplied in a pin configuration similar to that ol the popular
AD521 instrumentation amplificr.
OUTLINE DIMENSIONS
Dimensions shown in inches and (mm).
jun :22 II .
_ 'aasammi -'
'l'lJl-)'d 0]“)!le uleuJ
H "'m"c'"; "00,'it17
I - mrwm
s,,,,,,,,-,, P:;g;;;g;;_+
1‘5 "’5’ J—fi a 02510 M)
Unrvtq4ht - t
- -. -
02:6I6JII , ' I
.52) l
DDZOIILEII
(3PLACE sl 0mm“, _‘H‘meauuu
14-Pin DuaI-ln-Line Metal Package
Huumwm m
--r%'thlh9 m mm
mm BEAD sumo”
Jai- N vmnm
J,, .- '13: IW,
iria"" t
1qgu1.1AN
'umunn
mm it -
mm tip, nan m.
"W- Hog,':;
14-Pin DuaI-In-Linc Ceramic Package
P.0. Box 280, Norwood, Massachusetts 02062 U.S.A.
Tel:617/329A7tm Twx: 710/394A9577
Telex: 924491 Cables: ANALOG NORWOODMASS
I = - ' = -
S ECI ICA IONS (typ cal tr'1(si; +15V /IL 2m & TA - ps f u/ol1ss othtrt(its!yti!itd), TVV
Cam Equation
mm Range
qunnn Error
L l 1000
Nonlinearity max (see Fig r,
l, 7 I
c, 7 [mm
" Imp. max
G = 1000
OUTPUT CHARACTERISTICS
Output Ranng
DYNAMIC RESPONSF (see Fig 6)
Small Signal (-3413)
G 1 I00
Full Powcr GBW
Slew Rate
Scttltng lime to 0 1%. G " Inn
to OJIIWL G = [00
mnum,r.:10
to 0.01%, G ' 1
VOLT AGE OFFSFT
Offsets Referred to Input
Imnal Ottget Voiuge
(adjustable to Lrvu)
vs. Temperature, max (sec Frg, 3)
G -- 1000
1 < G < 1000
" Supply, max
G = 1000
INPUTCURRENTS
Input Bas Current
lmml max. 6255C
vs. lcmpcratulc
Input Offsc: Currcnt
Inmal max, +25"C
" remperature
Input Impedance
Drffereniiisl
Common Mode
Input Voltage Range
Maximum Differential Input, Lrtear
szlmum Diffzrcnnal Input, Safe
Maximum Common Mode. Linear
Mammum Common Mode Input, Sate
Common Mode RJcction Rado.
Min @:IOV,I1
Imbalance (see Fig. 5)
G = 1 (dc to IOHH
G = 10 (dc m lOHz)
G _ 100(dr ta 3H1)
c, =l000(dctolHer
G - l to I000 (dc to 60ilzy
Voltage Noise. RTI (sec Fig Al
0.1": m 100Uz (ppt
G = 1000
IOHI. to 10kHz (rms)
TFMPERATURE RANGE
Specified Performance
Upfrlllng
Storage
PUWER SUPPLY
Power Supply Range
Quiescent Current. mu 0 115V
PACKAGE
ADSZZAD
' 2110 )
l tO 1000
u 2% mu
1.0% max
0.005%
2ppm/‘u uppnu’c lyp)
sppprn(oqkspirrr/r, typ)
t10V 43.1 SmA
300kHz
l SRHL
0 lVIps
:4oouv mu (:zuouv typy
-"0yy,' C1210uV/ C ryp)
:buV' c
-'iHr6)gIV/C'
:zouw'x
tD zuvm
uoopA/"c
tt 00pA/“c
75dB (90dR lyp)
9MB (moan tyiO
moan (1 10cm lyp)
100113 (12043 typ)
vsdmasda lyp)
-25°C (0 wes"r:
-ss'cro o125”c
"rs''qto t1so''y
M5 [0 law
t10rnA
ceramic'
.AoszzBD
o 05% max
Ih2% max
:20an' max(1100thyP)
:zsuw°c "svv/'c typ)
t2uvfr.
-'(--' f 2) VI f
MhlBii00db Ky)”
95m; (1 10dB typ)
moan moan typ)
l10dB (>1200 wp)
soaa (88dg typ)
Ceram ics
Aozasryspttuyrsyt
.a...-..
zzoouv mu (ti00yV typ)
tiooiswocitwiswnc lyp)
ttvvi'c'
n ' omw c
7MB l90dB WP)
9043 (HMS typ)
mods (12043 ryp)
moan (>I20deyp)
'Speciricuions am: u AD522A
"Speuhnnnns am: Is ADSZZB
Sprciticuions subiect to change wnhoul none!
'Specifi tionsguatuircrd arm no minult wlmup
ITh: ADDZISD I) Ivlllahlr protexu-d In MILSTD‘IHS. Level B.
' Analog Devices Irsuvcs the nght to ship mm: "rckages m licu
of the umdud rennin plclugo. IurA and B gums.
s'i,i'iratitl
DERATIONS
Figure 1 illustrates the AD522 wiring configuration when used
in a typical bridge amplifier application. In any low-level, high
impedance, moise-dominated environment, proper shielding and
grounding are requisite for optimum performance; a recommen-
ded technique is shown.
smut navunw GROUND
LOAD RETURN
()[imi <=+ ell
I cam nmsmn Ra swouin BE _ c wusun TYPE ntcommmmui
2 SHlELDED CO~~ICVIDNS m is R(COIAMENOHJ WHEN MAXIMUM "STEM BANEMIDYN
no AC cum l8 umtnnsu, Am: mien Ra Is LOCA'EDMOKE mm SlK mcuss mom
ACWTd Ntl INSTABLLIIIES ARE CAUSEO av REMOVE no LOCATIONS mew Nor ism,
THE nu GUARD um CAN Ile tin uncnuwmw
3 row“ suuu Mums ARE nzcmmsuutu FOE mmuw NOISE w NUISV ENVIRON
A No min nkuumm ma MUST mscnmns " ntoumeu A me; _ c. Mi TURN
mm mi vsucn As VISI‘AY um v mu IS nteawmezo
Figure 1. Typical Bridge Application
Direct coupling of the AD522 inputs makes it necessary to
provide a signal ground return for input amplifier bias currents.
This can be achieved by direct connection as shown, or through
an indirect path of less than 1M9 resistance such as other sys-
tem interconnections.
To minimize noise, shielding should be provided for the input
leads and gain resistor connections. A passive data guard is pro-
vided to improve ac common mode rejection by "bootstrap-
ping" the capacitance of the input cabling, thus minimizing
differential phase shift. This will also reduce degradation of
system bandwidth.
Balanced design eliminates the need for external bypass caIra-
citors for most applications. If, however, the power supplies
are remotely located (farther than 10 feet or so) or if they are
likely to carry more than a few millivolts of noise, local filter-
ing will enable the user to retain optimal performance.
Reference and sense pins are provided to permit remote load
Effect on Absolute
strnsing. These points can also be used to trim the device CMR,
add an output booster, or to offset the output to a reference
level. These applications are illustrated in following sections.
It is good practice to place RG within several inches of the
AD522. Longer leads will increase stray capacitance and cause
phase shifts that will degrade CMR at higher frequencies. For
frequencies below lOHz, a remote RG is generally acceptable;
no stability problems are caused, Beat in mind that a leakage
impedance of ZOUMQ between RC pins will cause an 0.1% gain
error at G = l. Unity gain is not trimmahle.
TYPICAL APPLICATION AND ERROR BUDGET ANALYSIS
(See Figure 1 and Table "
A floating transducer with a 0 to 1 volt output has a Iki2 source
imbalance. A noisy environment induces a one volt o to 60Hz
common mode signal in the ground return. This signal must be
amplified to interface with a data acquisition system calibrated
for a 0 to 10 volt signal range. The operating temperature range
is f) to +50°C and an ADSZZB is to be used. Table 1 lists
error sources and their effect on system accuracy.
The total effect on absolute accuracy is less than 10. 2%, allowing
adjustment-free 8-bit operation. In computer or microprocer
sor controlled data-acquisition systems, automatic recalibration
can nullify gain and offset drifts leaving noise, distortion and
CMR as the only error sources. In this case, full 12-bit opera-
tion is achieved.
Gain Errors: Absolute gain errors can be nulled by trimming
RC. Gain drift is a. linear effect, not detrimental to resolution
and is caused by the change in value of internal resistors over
the operating temperature range. An "intelligent" system can
correct for these errors with an automatic calibration cycle,
Gain nonlinearity never exceeds 0.002% at G = 10,
Offset Drift & Pins Current Errors.. Special care has been taken
in the dcsign of the ADS 22 input stage to minimize offset drift.
Unless transducer impedances are unbalanced by more than
2KS2, errors caused by offset current drift are negligible com-
pared to offset voltage drift. Although initial offset voltages
are laser-nulled for most applications, provisions have been
made to allow further adjustment to correct for initial system
offset. In this example, all offset drifts amou m to $0.014%
and do not effect resolution (can be corrected with an auto-
matic calibration cycle).
CMR and Noise Errors: Common mode rejection and noise
performance of instrumentation amplifiers are critical because
Effect on Resolution
PIN CON FIGURATION
Error Source Sprcificiatio" Accuracy. %of RS. % of FS,
unrut E n R mm
Gain Nonlinearity $000236 max, G = 10 Mhu02 10,002
(from Spec. Sheet and Fig, 4) mm E muaunn
Voltage Drift 2%}:19 f 2 oiiw"c : 4.5pw°c 10.011 _ - - mvuv E SENSE
R.Tl = o mmssw C uqu m m
(from Spec Sheet)
CMR 86dB (from Spec, Sheet, CMR vs F tO 005 10,005 V E "C
vs, G, typical curve) mm [11 a. mo
NOISC, R.T O 15u\' (p-p) R.T.O (from Spec, Sheet. 20.0015 100015 _
(0,1 to 100Hc) Noise vs. G typtcal rune) cum" E m, vnEw u "
Offset Current ISUpA/oc K 1k source Imbalance to 000125 -
Drift (Spec. Sheet) t :swvx"c x
:1 25W WI L
Gain Drift ooppmr'c: t0.15 -
(add toppmi‘k for
external Rc)
(Spec. Shccll
Table t. Error Sources
these errors can not be corrected by calibration. Common mode
rejection of the AD522 is active laser-trimmed to the limits of
thin-film resistor stability. Further trimming could improve
CMR on a short term basis, but regular readjustment would be
necessary to maintain this improvement (see Figure 2). In this
example, untrimmed CMR and noise cause a total error of
t0.0065% of full scale and are the major contributors to reso-
lution error.
Figure 2. Optional CMR Trim
PERFORMANCE CHARACTERISTICS
Offset Voltage and Current Drift: The AD522 is available in
four drift selections. Figure 3 is a graph of maximum RTO off-
set voltage drift vs. gain for all versions. Errors caused by off-
set voltage drift can thus be determined for any gain. Offset
current drift will cause a voltage error equal to the product of
the offset current drift and the source impedance unbalance.
.. ,.i
MAXVIUMMFSEYDRIFV
. w: Aoszu ,
mmuv arrstr mun aw c
ttefr=---"
l " mo mun
GAIN 7 WV
F igure 3. Output Offset Drift (R TO) vs. Gain
Gain Nonlinearity and Noise.. Gain nonlinearity increases with
gain as the device lnopgain decreases. Figure 4 is a plot of
typical nonlinearity vs. gain. The shape of the curve can be
safely used to predict worst-case nonlinearity at gains below
100. Noise vs. gain is shown on the same graph.
rv-ruu. nous, am in m mm. 3 a.
nu. Am _
am: i t .
NOISE tum) - mv p-v
yummy MOHLII‘AIIW noun
aAmuoNLmumlv unm- ‘ulhlimlzwvdul
uxmuu Nowtuuunm
l to TIA um
mun VN
Figure 4. Gain Nonlinearity and Noise (R TO) vs. Gain
Common Mode Rejection.. CMR is rated at t10hr and lkQ
source imbalance. At lower gains, CMR depends mainly on
thin-film resistor stability but due to gain-bandwidth consider-
ations, is relatively constant with frequency to beyond 60Hz.
The dc CMR improves with increasing gain and is increasingly
subject to phase shifts in limited bandwidth highgain ampli-
fiers. Figure 5 illustrates CMR vs. Gain and Frequency.
Dynamic Performance: Settling time and unity gain bandwidth
are directly proportional to gain. As a result, dynamic perfor-
mance can be predicted from the well-behaved curves of
Figure 6.
'i' M i i
vacAi [DN‘Alh7n
r " tr: manner
© 'Invmv
i u: * ("'-vl"-[cm'''ot"'o-vocTAoE
mt sunset mut wnvtscm,
" usen m Puma tmcn om
vs mm M!) rnmuzucv run
mu mu 5
t m "to mm
rnmumu - m
Figure 5. Common Mode Rejection vs Frequency and Gain
mun» SMALL SlGNAL
rnmutucv RESVONSE
azsmnst
RESPONSE
AMPIIHIR mm In
m _ i, T _ 1- ion mm m
vnroumcv-Hx-
Figure 6. Small Signal Frequency Response (-3118)
SPECIAL APPLICATIONS
Offset and Gain Trim.. Gain accuracy depends largely on the
quality of RC. A prccision resistor with a lOppm/OC tempera-
ture coefficient is advised. Offset, like gain, is laser-trimmed to
a level suitable for most applications. If further adjustment is
required, the circuit shown in Figure l is recommended. Note
that good quality (25ppm) pots are necessary to maintain vol-
tage drift specifications.
CMR Trim: A short-term CMR improvement of up to lOdB at
low gains can be realized with the circuit of Figure 2. Apply a
low-frcquency 20/G volt pcak-to-peak input signal to both
inputs through their equivalent source resistances and trim the
pot for an ac output null.
Sense Output: A sense output is provided to enable remote
load sensing or use of an output current booster. Figure 7 illu-
stratus these applications. Being "inside the loop", booster
drift errors are minimized. When not used, the sense output
should be tied to the output.
_ Iunouvvuu
irvnwn
Figure Jr. Output Current Booster and Buffered Output
Level Shifter
Reference Output: The reference terminal is provided to permit
the user to offset or "level shift'' the output level to a datum
compatible with his load. It must be remembered that the total
output swing is :10 volts to be shared between signal and refer-
ence offset, Furthermore, any reference source resistance will
unbalance the CMR trim by the ratio 10k/Rtei. For example, if
the reference source impedance is In, CMR will be reduced to
80dB(10kQ/1§2 = 10,000 = 80dB). A buffer amplifier can be
used to eliminate this error, as shown in Figure 7, but the
drift of the buffer will add to output offset drift, When not
used, the reference terminal should be grounded.
C393: -5-8l83
PRINTED IN U.S.A.
