AD AD711KN Precision, low cost, high speed, bifet op amp Datasheet

a
FEATURES
Enhanced Replacement for LF411 and TL081
AC PERFORMANCE
Settles to ⴞ0.01% in 1.0 ␮s
16 V/␮s min Slew Rate (AD711J)
3 MHz min Unity Gain Bandwidth (AD711J)
DC PERFORMANCE
0.25 mV max Offset Voltage: (AD711C)
3 ␮V/ⴗC max Drift: (AD711C)
200 V/mV min Open-Loop Gain (AD711K)
4 ␮V p-p max Noise, 0.1 Hz to 10 Hz (AD711C)
Available in Plastic Mini-DIP, Plastic SOIC, Hermetic
Cerdip, and Hermetic Metal Can Packages
MIL-STD-883B Parts Available
Available in Tape and Reel in Accordance with
EIA-481A Standard
Surface Mount (SOIC)
Dual Version: AD712
PRODUCT DESCRIPTION
The AD711 is a high speed, precision monolithic operational
amplifier offering high performance at very modest prices. Its
very low offset voltage and offset voltage drift are the results of
advanced laser wafer trimming technology. These performance
benefits allow the user to easily upgrade existing designs that use
older precision BiFETs and, in many cases, bipolar op amps.
The superior ac and dc performance of this op amp makes it
suitable for active filter applications. With a slew rate of 16 V/ms
and a settling time of 1 ms to ± 0.01%, the AD711 is ideal as a
buffer for 12-bit D/A and A/D Converters and as a high-speed
integrator. The settling time is unmatched by any similar IC
amplifier.
The combination of excellent noise performance and low input
current also make the AD711 useful for photo diode preamps.
Common-mode rejection of 88 dB and open loop gain of
400 V/mV ensure 12-bit performance even in high-speed unity
gain buffer circuits.
The AD711 is pinned out in a standard op amp configuration
and is available in seven performance grades. The AD711J and
AD711K are rated over the commercial temperature range of
0∞C to 70∞C. The AD711A, AD711B and AD711C are rated
over the industrial temperature range of –40∞C to +85∞C. The
AD711S and AD711T are rated over the military temperature
range of –40∞C to +125∞C and are available processed to MILSTD-883B, REV. E.
Precision, Low Cost,
High Speed, BiFET Op Amp
AD711
CONNECTION DIAGRAMS
OFFSET
NULL
NC
+VS
INVERTING
INPUT
OUTPUT
AD711
NON
INVERTING
INPUT
OFFSET
NULL
–VS
10k⍀
NC = NO CONNECT
–15V
NOTE
PIN 4 CONNECTED TO CASE
OFFSET
NULL
INVERTING
INPUT
NONINVERTING
INPUT
–VS
VOS TRIM
1
8
NC
2
7
+VS
3
6
4
5
OUTPUT
OFFSET
NULL
AD711
NC = NO CONNECT
Extended reliability PLUS screening is available, specified over
the commercial and industrial temperature ranges. PLUS
screening includes 168 hour burn-in, as well as other environmental and physical tests.
The AD711 is available in an 8-pin plastic mini-DIP, small
outline, cerdip, TO-99 metal can, or in chip form.
PRODUCT HIGHLIGHTS
1. The AD711 offers excellent overall performance at very
competitive prices.
2. Analog Devices’ advanced processing technology and 100%
testing guarantee a low input offset voltage (0.25 mV max,
C grade, 2 mV max, J grade). Input offset voltage is specified
in the warmed-up condition. Analog Devices’ laser wafer
drift trimming process reduces input offset voltage drifts to
3 mV/∞C max on the AD711C.
3. Along with precision dc performance, the AD711 offers
excellent dynamic response. It settles to ± 0.01% in 1 ms and
has a 100% tested minimum slew rate of 16 V/ms. Thus this
device is ideal for applications such as DAC and ADC
buffers which require a combination of superior ac and dc
performance.
4. The AD711 has a guaranteed and tested maximum voltage
noise of 4 mV p-p, 0.1 to 10 Hz (AD711C).
5. Analog Devices’ well-matched, ion-implanted JFETs ensure
a guaranteed input bias current (at either input) of 25 pA
max (AD711C) and an input offset current of 10 pA max
(AD711C). Both input bias current and input offset current
are guaranteed in the warmed-up condition.
REV. E
Information furnished by Analog Devices is believed to be accurate and
reliable. However, no responsibility is assumed by Analog Devices for its
use, nor for any infringements of patents or other rights of third parties that
may result from its use. No license is granted by implication or otherwise
under any patent or patent rights of Analog Devices.
One Technology Way, P.O. Box 9106, Norwood, MA 02062-9106, U.S.A.
Tel: 781/329-4700
www.analog.com
Fax: 781/326-8703
© Analog Devices, Inc., 2002
AD711–SPECIFICATIONS (V = 15 V @ T = 25C, unless otherwise noted.)
S
Parameter
Min
INPUT OFFSET VOLTAGE1
Initial Offset
TMIN to TMAX
vs. Temp
vs. Supply
76
TMIN to TMAX
76/76/76
Long-Term Stability
INPUT BIAS CURRENT2
VCM = 0 V
VCM = 0 V @ TMAX
VCM = ± 10 V
3.0
16
Current
POWER SUPPLY
Rated Performance
Operating Range
Quiescent Current
Min
2/1/1
3/2/2
20/20/20
K/B/T
Typ
0.2
5
100
80
80
50
1.1/3.2/51
100
15
20
25
0.6/1.6/26
5
3.4
4.0
200
20
1.0
0.0003
18
1.2
Min
0.5
1.0
10
C
Typ
0.10
86
86
2
110
Max
Unit
0.25
0.45
5
mV
mV
mV/∞C
dB
dB
mV/Month
25
1.6
50
pA
nA
pA
10
0.65
pA
nA
15
50
1.1/3.2/51
100
15
20
25
0.6/1.6/26
5
3.4
18
1.2
4.0
200
20
1.0
0.0003
1.2
MHz
kHz
V/ms
ms
%
3 ¥ 1012储5.5
3 ¥ 1012储5.5
3 ¥ 1012储5.5
3 ¥ 1012储5.5
3 ¥ 1012储5.5
3 ¥ 1012储5.5
W储pF
W储pF
± 20
+14.5, –11.5
± 20
+14.5, –11.5
± 20
+14.5, –11.5
V
+VS – 2
88
84
84
80
–VS + 4
80
80
76
74
+VS – 2
88
84
84
80
0.01
+13, –12.5 +13.9, –13.3
± 12/± 12/± 12 +13.8, –13.1
25
+13, –12.5 +13.9, –13.3
± 12
+13.8, –13.1
25
2.5
86
86
76
74
± 18
3.4
400
± 4.5
± 15
2.5
+V – 2 V
94
90
90
84
2
45
22
18
16
0.01
200
100
± 15
–VS + 4
2
45
22
18
16
150
400
100/100/100
± 4.5
Max
15
2
45
22
18
16
INPUT CURRENT NOISE
OUTPUT
CHARACTERISTICS
Voltage
4.0
200
20
1.0
0.0003
–VS + 4
76
76/76/76
70
70/70/70
Max
15
10
INPUT VOLTAGE NOISE
OPEN-LOOP GAIN
7
95
20
INPUT IMPEDANCE
Differential
Common Mode
INPUT VOLTAGE RANGE
Differential3
Common-Mode Voltage4
TMIN to TMAX
Common-Mode
Rejection Ratio
VCM = ± 10 V
TMIN to TMAX
VCM = ± 11 V
TMIN to TMAX
0.3
15
INPUT OFFSET CURRENT
VCM = 0 V
VCM = 0 V @ TMAX
FREQUENCY RESPONSE
Small Signal Bandwidth
Full Power Response
Slew Rate
Settling Time to 0.01%
Total Harmonic Distortion
J/A/S
Typ
A
200
100
dB
dB
dB
dB
4
0.01
pA/÷Hz
400
V/mV
V/mV
+13, –12.5 +13.9, –13.3
± 12
+13.8, –13.1
25
± 18
3.0
± 4.5
mV p-p
nV/÷Hz
nV/÷Hz
nV/÷Hz
nV/÷Hz
± 15
2.5
V
V
mA
± 18
2.8
V
V
mA
NOTES
1
Input Offset Voltage specifications are guaranteed after 5 minutes of operation at T A = 25∞C.
2
Bias Current specifications are guaranteed maximum at either input after 5 minutes of operation at T A = 25∞C. For higher temperatures, the current doubles every 10∞C.
3
Defined as voltage between inputs, such that neither exceeds ± 10 V from ground.
4
Typically exceeding –14.1 V negative common-mode voltage on either input results in an output phase reversal.
Specifications subject to change without notice.
–2–
REV. E
AD711
ABSOLUTE MAXIMUM RATINGS 1
Supply Voltage . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ± 18 V
Internal Power Dissipation2 . . . . . . . . . . . . . . . . . . . . . 500 mW
Input Voltage3 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ± 18 V
Output Short Circuit Duration . . . . . . . . . . . . . . . . . Indefinite
Differential Input Voltage . . . . . . . . . . . . . . . . . . +VS and –VS
Storage Temperature Range (Q, H) . . . . . . . –65∞C to +150∞C
Storage Temperature Range (N) . . . . . . . . . . –65∞C to +125∞C
Operating Temperature Range
AD711J/K . . . . . . . . . . . . . . . . . . . . . . . . . . . 0∞C to +70∞C
AD711A/B/C . . . . . . . . . . . . . . . . . . . . . . . . –40∞C to +85∞C
AD711S/T . . . . . . . . . . . . . . . . . . . . . . . . . –55∞C to +125∞C
Lead Temperature Range (Soldering 60 sec) . . . . . . . . . 300∞C
NOTES
1
Stresses above those listed under “Absolute Maximum Ratings” may cause
permanent damage to the device. This is a stress rating only and functional
operation of the device at these or any other conditions above those indicated in
the operational section of this specification is not implied. Exposure to absolute
maximum rating conditions for extended periods may affect device reliability.
2
Thermal Characteristics:
8-Pin Plastic Package:
qJC = 33∞C/Watt; qJA = 100∞C/Watt
8-Pin Cerdip Package:
qJC = 22∞C/Watt; qJA = 110∞C/Watt
8-Pin Metal Can Package:
qJC = 65∞C/Watt; qJA = 150∞C/Watt
8-Pin SOIC Package:
qJC = 43∞C/Watt; qJA = 160∞C/Watt
3
For supply voltages less than ± 18 V, the absolute maximum input voltage is equal
to the supply voltage.
ORDERING GUIDE
Model
*AD711AH
AD711AQ
*AD711BQ
*AD711CH
AD711JN
AD711JR
AD711JR-REEL
AD711JR-REEL7
AD711KN
AD711KR
AD711KR-REEL
AD711KR-REEL7
*AD711SQ/883B
*AD711TQ/883B
Temperature
Range
–40∞C to +85∞C
–40∞C to +85∞C
–40∞C to +85∞C
–40∞C to +85∞C
0∞C to 70∞C
0∞C to 70∞C
0∞C to 70∞C
0∞C to 70∞C
0∞C to 70∞C
0∞C to 70∞C
0∞C to 70∞C
0∞C to 70∞C
–55∞C to +125∞C
–55∞C to +125∞C
8-Pin Metal Can
8-Pin Ceramic DIP
8-Pin Ceramic DIP
8-Pin Metal Can
8-Pin Plastic DIP
8-Pin Plastic SOIC
8-Pin Plastic SOIC
8-Pin Plastic SOIC
8-Pin Plastic DIP
8-Pin Plastic SOIC
8-Pin Plastic SOIC
8-Pin Plastic SOIC
8-Pin Ceramic DIP
8-Pin Ceramic DIP
Package
Option*
H-08A
Q-8
Q-8
H-08A
N-8
RN-8
RN-8
RN-8
N-8
RN-8
RN-8
RN-8
Q-8
Q-8
*Not for new design, obsolete April 2002
CAUTION
ESD (electrostatic discharge) sensitive device. Electrostatic charges as high as 4000 V readily
accumulate on the human body and test equipment and can discharge without detection. Although
the AD711 features proprietary ESD protection circuitry, permanent damage may occur on devices
subjected to high-energy electrostatic discharges. Therefore, proper ESD precautions are
recommended to avoid performance degradation or loss of functionality.
REV. E
Package
Description
–3–
WARNING!
ESD SENSITIVE DEVICE
AD711–Typical Performance Characteristics
10
RL = 2k
25C
5
0
5
10
15
SUPPLY VOLTAGE – Volts
+VOUT
10
RL = 2k
25C
5
0
–VOUT
0
5
10
15
SUPPLY VOLTAGE – Volts
–6
–8
10
5
10
15
SUPPLY VOLTAGE – Volts
20
–9
10
–10
0.01
0.01
1k
0 20 40 60 80 100 120 140
TEMPERATURE – C
TPC 5. Input Bias Current vs. Temperature
SHORT CIRCUIT CURRENT LIMIT – mA
INPUT BIAS CURRENT – pA
1
MAX J GRADE LIMIT
25
–5
0
5
COMMON MODE VOLTAGE – Volts
10
TPC 7. Input Bias Current vs. Common Mode Voltage
10k
100k
1M
FREQUENCY – Hz
10M
TPC 6. Output Impedance vs. Frequency
26
50
0
–10
–12
–60 –40 –20
100
75
10k
–11
10
TPC 4. Quiescent Current vs. Supply Voltage
VS = 15V
25C
100
1k
LOAD RESISTANCE – 10
5.0
24
+OUTPUT CURRENT
22
20
18
–OUTPUT CURRENT
16
14
12
10
–60 –40 –20 0 20 40 60 80 100 120 140
AMBIENT TEMPERATURE – C
TPC 8. Short Circuit Current Limit
vs. Temperature
–4–
UNITY GAIN BANDWIDTHT – MHz
0
5
AVCL = 1
10
1.75
10
–7
10
10
2.00
15V SUPPLIES
15
100
OUTPUT IMPEDANCE – INPUT BIAS CURRENT (VCM = 0) – Amps
2.25
20
TPC 3. Output Voltage Swing vs.
Load Resistance
10
2.50
25
0
10
20
TPC 2. Output Voltage Swing vs.
Supply Voltage
2.75
QUIESCENT CURRENT – mA
15
20
TPC 1. Input Voltage Swing vs.
Supply Voltage
OUTPUT VOLTAGE SWING – Volts p-p
15
0
30
20
OUTPUT VOLTAGE SWING – Volts
INPUT VOLTAGE SWING – Volts
20
4.5
4.0
3.5
3.0
–60 –40 –20 0 20 40 60 80 100 120 140
TEMPERATURE – C
TPC 9. Unity Gain Bandwidth vs.
Temperature
REV. E
AD711
80
120
GAIN
40
40
20
20
RL = 2k
C = 100pF
–20
10
100
1k
10k
100k
FREQUENCY – Hz
1M
–20
10M
95
OUTPUT VOLTAGE – Volts p-p
CMR – dB
40
20
100
1k
10k
100k
FREQUENCY – Hz
1M
INPUT NOISE VOLTAGE – nV/ Hz
–90
–100
–110
–120
100k
TPC 16. Total Harmonic Distortion vs. Frequency
40
VS = 15 SUPPLIES
WITH 1V p-p SINE
WAVE 25 C
20
10
100
1k
10k
10k
SUPPLY MODULATION FREQUENCY – Hz
2
25
20
15
10
5
1M
INPUT FREQUENCY – Hz
10M
8
6
4
2
1% 0.1% 0.01%
0
ERROR
–2
1% 0.1% 0.01%
–4
–6
–8
–10
0.5
0.6
0.7
0.8
0.9
SETTLING TIME – s
1.0
TPC 15. Output Swing and Error
vs. Settling Time
25
20
100
10
15
10
5
1
1k
10k
FREQUENCY – Hz
–SUPPLY
60
TPC 12. Power Supply Rejection
vs. Frequency
1k
3V RMS
RL = 2k
CL = 100pF
+SUPPLY
80
1
TPC 14. Large Signal Frequency
Response
–70
100
0
20
RL = 2k
25 C
VS = 15V
0
100k
TPC 13. Common Mode Rejection
vs. Frequency
THD – dB
5
10
15
SUPPLY VOLTAGE – Volts
30
60
REV. E
0
TPC 11. Open-Loop Gain vs.
Supply Voltage
VS = 15V
VCM = 1V p-p
25 C
80
–130
100
105
100
100
–80
110
0
TPC 10. Open-Loop Gain and
Phase Margin vs. Frequency
0
10
115
OUTPUT SWING FRIM 0V TO Volts
0
POWER SUPPLY REJECTION – dB
60
60
110
RL = 2k
25C
SLEW RATE – Vs
OPEN LOOP GAIN – dB
125
OPEN-LOOP GAIN – dB
PHASE
80
100
PHASE MARGIN – Degrees
100
1
10
100
1k
FREQUENCY – Hz
10k
TPC 17. Input Noise Voltage
Spectral Density
–5–
100k
0
0
100 200 300 400 500 600 700 800 900
INPUT ERROR SIGNAL – mV
(AT SUMMING JUNCTION)
TPC 18. Slew Rate vs. Input
Error Signal
AD711
25
24
SLEW RATE – V/s
23
22
+VS
0.1F
+VS
+VS
0.1F 1.3Mk
0.1F
21
10k
20
19
INPUT
18
AD711
AD711
OUTPUT
0.1F
2k
100pF
AD711
17
0.1F
16
0.1F
10k
–VS
–VS
15
–60 –40 –20 0 20 40 60 80 100 120 140
TEMPERATURE – C
TPC 19. Slew Rate vs. Temperature
+VS
0.1F
SQUARE WAVE
INPUT
TPC 21. Offset Null Configurations
0.1F
AD711
VIN
TPC 20. T.H.D. Test Circuit
–VS
RL
2k
VOUT
CL
100pF
–VS
TPC 22a. Unity Gain Follower
TPC 22b. Unity Gain Follower
Pulse Response (Large Signal)
TPC 22c. Unity Gain Follower
Pulse Response (Small Signal)
TPC 23b. Unity Gain Inverter
Pulse Response (Large Signal)
TPC 23c. Unity Gain Inverter Pulse
Response (Small Signal)
5k
+VS
VIN
0.1F
5k
AD711
0.1F
SQUARE WAVE
INPUT
RL
2k
VOUT
CL
100pF
–VS
TPC 23a. Unity Gain Inverter
–6–
REV. E
AD711
In addition to a significant improvement in settling time, the
low offset voltage, low offset voltage drift, and high open-loop
gain of the AD711 family assures 12-bit accuracy over the full
operating temperature range.
OPTIMIZING SETTLING TIME
Most bipolar high-speed D/A converters have current outputs;
therefore, for most applications, an external op amp is required
for current-to-voltage conversion. The settling time of the
converter/op amp combination depends on the settling time of
the DAC and output amplifier. A good approximation is:
t S Total = (t S DAC )2 + (t S AMP )2
The excellent high-speed performance of the AD711 is shown
in the oscilloscope photos of Figure 2. Measurements were taken
using a low input capacitance amplifier connected directly to the
summing junction of the AD711 – both photos show the worst
case situation: a full-scale input transition. The DAC’s 4 kW
[10 kW储8 kW = 4.4 kW] output impedance together with a 10 kW
feedback resistor produce an op amp noise gain of 3.25. The
current output from the DAC produces a 10 V step at the op
amp output (0 to –10 V Figure 2a, –10 V to 0 V Figure 2b.)
(1)
The settling time of an op amp DAC buffer will vary with the
noise gain of the circuit, the DAC output capacitance, and with
the amount of external compensation capacitance across the
DAC output scaling resistor.
Therefore, with an ideal op amp, settling to ± 1/2 LSB (± 0.01%)
requires that 375 mV or less appears at the summing junction.
This means that the error between the input and output (that
voltage which appears at the AD711 summing junction) must
be less than 375 mV. As shown in Figure 2, the total settling time
for the AD711/AD565 combination is 1.2 microseconds.
Settling time for a bipolar DAC is typically 100 ns to 500 ns.
Previously, conventional op amps have required much longer
settling times than have typical state-of-the-art DACs; therefore,
the amplifier settling time has been the major limitation to a
high-speed voltage-output D-to-A function. The introduction
of the AD711/712 family of op amps with their 1 ms (to ± 0.01%
of final value) settling time now permits the full high-speed
capabilities of most modern DACs to be realized.
0.1F
BIPOLAR
OFFSET ADJUST
REF
OUT
R2
GAIN 100
ADJUST
10V
20k
–VEE
20V
SPAN
POWER
GND
10pF
5k
9.95k
10V
SPAN
0.5mA
IREF
0.1F
BIPOLAR
OFF
AD565A
19.95k
REF
IN
REF
GND
R1
100
VCC
5k
DAC
IOUT = 4 IREF CODE
IO
5k
+15V
0.1F
DAC
OUT
AD711K
0.1F
OUTPUT
–10V TO +10V
–15V
MSB
LSB
Figure 1. ± 10 V Voltage Output Bipolar DAC
a. (Full-Scale Negative Transition)
b. (Full-Scale Positive Transition)
Figure 2. Settling Characteristics for AD711 with AD565A
REV. E
–7–
AD711
OP AMP SETTLING TIME—A MATHEMATICAL MODEL
The design of the AD711 gives careful attention to optimizing
individual circuit components; in addition, a careful tradeoff was
made: the gain bandwidth product (4 MHz) and slew rate
(20 V/ms) were chosen to be high enough to provide very fast
settling time but not too high to cause a significant reduction in
phase margin (and therefore stability). Thus designed, the AD711
settles to ± 0.01%, with a 10 V output step, in under 1 ms, while
retaining the ability to drive a 100 pF load capacitance when
operating as a unity gain follower.
If an op amp is modeled as an ideal integrator with a unity gain
crossover frequency of wo/2p, Equation 1 will accurately describe
the small signal behavior of the circuit of Figure 3a, consisting of
an op amp connected as an I-to-V converter at the output of a
bipolar or CMOS DAC. This equation would completely describe
the output of the system if not for the op amp’s finite slew rate
and other nonlinear effects.
VO
–R
=
R(C f = CX ) 2 Ê GN
I IN
ˆ
s +Á
+ RC f ˜ s + 1
wo
¯
Ë wo
(3)
where:
wo
=op amp’s unity gain frequency
2
op amp is being simulated or it is the combined capacitance of
the DAC output and the op amp input if the DAC buffer is
being modeled.
AD711
RIN
VIN
RL
R
Figure 3b. Simplified Model of the AD711
Used as an Inverter
In either case, the capacitance CX causes the system to go from
a one-pole to a two-pole response; this additional pole increases
settling time by introducing peaking or ringing in the op amp
output. Since the value of CX can be estimated with reasonable
accuracy, Equation 2 can be used to choose a small capacitor,
CF, to cancel the input pole and optimize amplifier response.
Figure 4 is a graphical solution of Equation 2 for the AD711
with R = 4 kW.
60
R ˆ
GN = “noise” gain of circuit ÁË1 + R ˜¯
O
GN = 4.0
50
GN = 3.0
This equation may then be solved for Cf:
GN = 2.0
40
2 - GN 2 RC X w o + (1 - GN )
+
Rw o
Rw o
(3)
CX
Cf =
CL
CX
p
Ê
VOUT
CF
30
GN = 1.5
In these equations, capacitor CX is the total capacitor appearing
the inverting terminal of the op amp. When modeling a DAC
buffer application, the Norton equivalent circuit of Figure 3a
can be used directly; capacitance CX is the total capacitance of
the output of the DAC plus the input capacitance of the op amp
(since the two are in parallel).
20
GN = 1.0
10
0
0
10
20
30
CF
40
50
60
Figure 4. Value of Capacitor CF vs. Value of CX
AD711
VOUT
CF
RL
The photos of Figures 5a and 5b show the dynamic response of
the AD711 in the settling test circuit of Figure 6.
CL
The input of the settling time fixture is driven by a flat-top pulse
generator. The error signal output from the false summing node
of A1 is clamped, amplified by A2 and then clamped again. The
error signal is thus clamped twice: once to prevent overloading
amplifier A2 and then a second time to avoid overloading the
oscilloscope preamp. The Tektronix oscilloscope preamp type
7A26 was carefully chosen because it does not overload with
these input levels. Amplifier A2 needs to be a very high speed
FET-input op amp; it provides a gain of 10, amplifying the error
signal output of A1.
R
IO
RO
CX
Figure 3a. Simplified Model of the AD711 Used as a
Current-Out DAC Buffer
When RO and IO are replaced with their Thevenin VIN and RIN
equivalents, the general purpose inverting amplifier of Figure 26b
is created. Note that when using this general model, capacitance
CX is either the input capacitance of the op amp if a simple inverting
–8–
REV. E
AD711
current-to-voltage converters. The use of a guarding technique
such as that shown in Figure 7, in printed circuit board layout
and construction is critical to minimize leakage currents. The
guard ring is connected to a low impedance potential at the
same level as the inputs. High impedance signal lines should
not be extended for any unnecessary length on the printed
circuit board.
4
4
5
5
3
6
2
3
2
6
Figure 5a. Settling Characteristics 0 to +10 V Step
Upper Trace: Output of AD711 Under Test (5 V/Div)
Lower Trace: Amplified Error Voltage (0.01%/Div)
1
8
1
7
7
8
Figure 7. Board Layout for Guarding Inputs
D/A CONVERTER APPLICATIONS
The AD711 is an excellent output amplifier for CMOS DACs.
It can be used to perform both 2-quadrant and 4-quadrant
operation. The output impedance of a DAC using an inverted
R-2R ladder approaches R for codes containing many 1s, 3R
for codes containing a single 1, and for codes containing all
zero, the output impedance is infinite.
For example, the output resistance of the AD7545 will modulate between 11 kW and 33 kW. Therefore, with the DAC’s
internal feedback resistance of 11 kW, the noise gain will vary
from 2 to 4/3. This changing noise gain modulates the effect of
the input offset voltage of the amplifier, resulting in nonlinear
DAC amplifier performance.
Figure 5b. Settling Characteristics 0 to –10 V Step
Upper Trace: Output of AD711 Under Test (5 V/Div)
Lower Trace: Amplified Error Voltage (0.01%/Div)
The AD711K with guaranteed 500 mV offset voltage minimizes
this effect to achieve 12-bit performance.
GUARDING
The low input bias current (15 pA) and low noise characteristics
of the AD711 BiFET op amp make it suitable for electrometer
applications such as photo diode preamplifiers and picoampere
5pF
AD3554
HP2835
205
VERROR 5
HP2835
0.47F
4.99k
4.99k
200k
DATA
DYNAMICS
5109
(OR
EQUIVALENT
FLAT TOP
PULSE
GENERATOR)
–15V
5-18pF
VIN
1.1k
10k
10k
0.47F
+15V
10k
0.2-0.0pF
VOUT
AD711
5k
10pF
0.1F
0.1F
–15V
+15V
Figure 6. Settling Time Test Circuit
REV. E
–9–
TEXTRONIX 7A26
OSCILLOSCOPE
PREAMP
INPUT SELECTION
1M
20pF
AD711
compared to a series of switched trial currents. The comparison
point is diode clamped but may deviate several hundred millivolts
resulting in high frequency modulation of A/D input current.
Figures 8 and 9 show the AD711 and AD7545 (12-bit CMOS
DAC) configured for unipolar binary (2-quadrant multiplication)
or bipolar (4-quadrant multiplication) operation. Capacitor C1
provides phase compensation to reduce overshoot and ringing.
Figures 10a and 10b show the settling time characteristics of the
AD711 when used as a DAC output buffer for the AD7545.
R2*
+15
VDD
GAIN
ADJUST
VIN
R1*
VDD
VREF
C1
33pF
0.1F
RFB OUT1
AD711K
AD7545
VOUT
DGND AGND
CF
0.1F
ANALOG
COMMON
DB11-DB0
*FOR VALUES R1 AND R2,
REFER TO TABLE 1
–15
a. Full-Scale Positive
Transition
Figure 8. Unipolar Binary Operation
Figure 10. Settling Characteristics for AD711 with AD7545
R1 and R2 calibrate the zero offset and gain error of the DAC.
Specific values for these resistors depend upon the grade of
AD7545 and are shown below.
compared to a series of switched trial currents. The comparison
point is diode clamped but may deviate several hundred millivolts resulting in high frequency modulation of A/D input
current. The output impedance of a feedback amplifier is made
artificially low by the loop gain. At high frequencies, where the
loop gain is low, the amplifier output impedance can approach
its open loop value. Most IC amplifiers exhibit a minimum open
loop output impedance of 25 W due to current limiting resistors.
A few hundred microamps reflected from the change in converter loading can introduce errors in instantaneous input
Table I. Recommended Trim Resistor Values vs. Grades
of the AD7545 for VDD = 5 V
TRIM
RESISTOR JN/AQ/SD KN/BQ/TD LN/CQ/UD GLN/GCQ/GUD
R1
R2
500 W
150 W
200 W
68 W
100 W
33 W
b. Full-Scale Negative
Transition
20 W
6.8 W
NOISE CHARACTERISTICS
12/8
The random nature of noise, particularly in the 1/f region, makes
it difficult to specify in practical terms. At the same time,
designers of precision instrumentation require certain guaranteed
maximum noise levels to realize the full accuracy of their equipment.
R/C
GAIN
ADJUST
R2
100
0.1F
OFFSET
ADJUST
An op amp driving the analog input of an A/D converter, such
as that shown in Figure 11, must be capable of maintaining a
constant output voltage under dynamically changing load conditions.
In successive-approximation converters, the input current is
VIN
R1*
CE
MIDDLE
BITS
REF IN
REF OUT
BIP OFF
10VIN
ANA COM
LOW
BITS
+5V
+15V
–15V
DIG COM
ANALOG COM
Figure 11. AD711 as ADC Unity Gain Buffer
C1
33pF
R4
20k
1%
+15V
0.1F
OUT1
VREF AD7545
AGND
DGND
DB11-DB0
0.1F
–15V
R2*
RFB
AD574
20VIN
AD711
10V
ANALOG
INPUT
DRIVING THE ANALOG INPUT OF AN A/D CONVERTER
VDD
R1
100
+15V
All other grades of the AD711 are sample-tested on an AQL
basis to a limit of 6 mV p-p, 0.1 to 10 Hz.
GAIN
ADJUST
HIGH
BITS
AO
The AD711C grade is specified at a maximum level of 4.0 mV p-p,
in a 0.1 Hz to 10 Hz bandwidth. Each AD711C receives a 100%
noise test for two 10-second intervals; devices with any excursion
in excess of 4.0 mV are rejected. The screened lot is then submitted
to Quality Control for verification on an AQL basis.
VDD
STS
CS
AD711K
R5
20k
1%
+15V
R3
10k
1%
0.1F
0.1F
AD711K
VOUT
0.1F
12
–15V
*FOR VALUES R1 AND R2,
REFER TO TABLE 1
DATA INPUT
ANALOG
COMMON
–15V
Figure 9. Bipolar Operation
–10–
REV. E
AD711
voltage. If the A/D conversion speed is not excessive and the
bandwidth of the amplifier is sufficient, the amplifier’s output
will return to the nominal value before the converter makes its
comparison. However, many amplifiers have relatively narrow
bandwidth yielding slow recovery from output transients. The
AD711 is ideally suited to drive high speed A/D converters since
it offers both wide bandwidth and high open-loop gain.
large value input resistors, bias currents flowing through these
resistors will also generate an offset voltage.
In addition, at higher frequencies, an op amp’s dynamics must
be carefully considered. Here, slew rate, bandwidth, and open-loop
gain play a major role in op amp selection. The slew rate must
be fast as well as symmetrical to minimize distortion. The amplifier’s
bandwidth in conjunction with the filter’s gain will dictate the
frequency response of the filter.
The use of a high performance amplifier such a s the AD711
will minimize both dc and ac errors in all active filter applications.
SECOND ORDER LOW PASS FILTER
a. Source Current = 2 mA
b. Sink Current = 1 mA
Figure 12. ADC Input Unity Gain Buffer Recovery Times
Figure 15 depicts the AD711 configured as a second order
Butterworth low pass filter. With the values as shown, the corner
frequency will be 20 kHz; however, the wide bandwidth of the
AD711 permits a corner frequency as high as several hundred
kilohertz. Equations for component selection are shown below.
R1 = R2 = user selected (typical values: 10 kW – 100 kW)
DRIVING A LARGE CAPACITIVE LOAD
The circuit in Figure 13 employs a 100 W isolation resistor which
enables the amplifier to drive capacitive loads exceeding 1500 pF;
the resistor effectively isolates the high frequency feedback from
the load and stabilizes the circuit. Low frequency feedback is
returned to the amplifier summing junction via the low pass
filter formed by the 100 W series resistor and the load capacitance, CL. Figure 14 shows a typical transient response for
this connection.
C1=
1.414
0.707
, C2 =
(2 p)( f cutoff )(R1)
(2 p)( f cutoff )(R1)
(5)
Where:
C1 and C2 are in farads.
C1
560pF
+15V
0.1F
R1
20k
4.99k
30pF
+VS
(4)
VIN
0.1F
R2
20k
C2
280pF
AD711
VOUT
0.1F
INPUT
4.99k
TYPICAL CAPACITANCE
LIMIT FOR VARIOUS
LOAD RESISTORS
RL
2k
10k
20k
CL UP TO
1500pF
1500pF
1000pF
AD711
0.1F
100
CL
OUTPUT
–15V
RL
–VS
Figure 13. Circuit for Driving a Large Capacitive Load
Figure 15. Second Order Low Pass Filter
An important property of filters is their out-of-band rejection.
The simple 20 kHz low pass filter shown in Figure 15, might be
used to condition a signal contaminated with clock pulses or
sampling glitches which have considerable energy content at
high frequencies.
The low output impedance and high bandwidth of the AD711
minimize high frequency feedthrough as shown in Figure 16.
The upper trace is that of another low-cost BiFET op amp
showing 17 dB more feedthrough at 5 MHz.
Figure 14. Transient Response RL = 2 kW, CL = 500 pF
ACTIVE FILTER APPLICATIONS
In active filter applications using op amps, the dc accuracy of the
amplifier is critical to optimal filter performance. The amplifier’s
offset voltage and bias current contribute to output error. Offset
voltage will be passed by the filter and may be amplified to produce
excessive output offset. For low frequency applications requiring
REV. E
Figure 16.
–11–
AD711
2-pole response; for a total of 8 poles. The 9th pole consists of a
0.001 mF capacitor and a 124 kW resistor at Pin 3 of amplifier A2.
Figure 18 depicts the circuits for each FDNR with the proper
selection of R. To achieve optimal performance, the 0.001 mF
capacitors must be selected for 1% or better matching and all
resistors should have 1% or better tolerance.
9-POLE CHEBYCHEV FILTER
Figure 17 shows the AD711 and its dual counterpart, the AD712,
as a 9-pole Chebychev filter using active frequency dependent
negative resistors (FDNR). With a cutoff frequency of 50 kHz
and better than 90 dB rejection, it may be used as an anti-aliasing
filter for a 12-bit data acquisition system with 100 kHz throughput.
As shown in Figure 17, the filter is comprised of four FDNRs (A,
B, C, D) having values of 4.9395 ⫻ 10–15 and 5.9276 ⫻
10–15 farad-seconds. Each FDNR active network provides a
+15V
0.1F
+15V
0.1F
VIN
0.001F
A1
2800
6190
6490
6190
2800
AD711
–15
4.9395E
0.1F
–15
5.9276E
–15
5.9276E
A2
–15
4.9395E
A
B
C
D
*
*
*
*
AD711
VOUT
0.1F
–15V
0.001
F
100k
*SEE TEXT
4.99k
124k
–15V
4.99k
Figure 17. 9-Pole Chebychev Filter
+15V
0.1F
0.001F
1/2
R
0.1F
1/2
AD712
AD712
0.001F
–15V
1k
R: 24.9k FOR 4.9395E–15
29.4k FOR 5.9276E–15
4.99k
Figure 18. FDNR for 9-Pole Chebychev Filter
Figure 19. High Frequency Response for 9-Pole
Chebychev Filter
–12–
REV. E
AD711
OUTLINE DIMENSIONS
8-Lead Plastic Dual-in-Line Package [PDIP]
(N-8)
8-Lead Ceramic Dip – Glass Hermetic Seal [CERDIP]
(Q-8)
Dimensions shown in inches and (millimeters)
Dimensions shown in inches and (millimeters)
0.005 (0.13)
MIN
0.375 (9.53)
0.365 (9.27)
0.355 (9.02)
8
8
5
0.295 (7.49)
0.285 (7.24)
0.275 (6.98)
4
1
0.310 (7.87)
0.220 (5.59)
1
0.100 (2.54)
BSC
0.320 (8.13)
0.290 (7.37)
0.405 (10.29) MAX
0.060 (1.52)
0.015 (0.38)
0.200 (5.08)
MAX
0.150 (3.81)
MIN
0.200 (5.08)
0.125 (3.18)
0.015 (0.38)
0.010 (0.25)
0.008 (0.20)
SEATING
PLANE
0.060 (1.52)
0.050 (1.27)
0.045 (1.14)
4
0.100 (2.54) BSC
0.150 (3.81)
0.135 (3.43)
0.120 (3.05)
0.015
(0.38)
MIN
0.150 (3.81)
0.130 (3.30)
0.110 (2.79)
0.022 (0.56)
0.018 (0.46)
0.014 (0.36)
5
PIN 1
0.325 (8.26)
0.310 (7.87)
0.300 (7.62)
0.180
(4.57)
MAX
0.055 (1.40)
MAX
0.023 (0.58)
0.014 (0.36)
SEATING
0.070 (1.78) PLANE
0.030 (0.76)
0.015 (0.38)
0.008 (0.20)
15
0
CONTROLLING DIMENSIONS ARE IN INCH; MILLIMETERS DIMENSIONS
(IN PARENTHESES) ARE ROUNDED-OFF MILLIMETER EQUIVALENTS FOR
REFERENCE ONLY AND ARE NOT APPROPRIATE FOR USE IN DESIGN
COMPLIANT TO JEDEC STANDARDS MO-095AA
CONTROLLING DIMENSIONS ARE IN INCHES; MILLIMETERS DIMENSIONS
(IN PARENTHESES)
8-Lead Standard Small Outline Package [SOIC]
Narrow Body
(RN-8)
8-Lead Metal Can [TO-99]
(H-8)
Dimensions shown in inches and (millimeters)
Dimensions shown in millimeters and (inches)
REFERENCE PLANE
5.00 (0.1968)
4.80 (0.1890)
5
1
4
1.27 (0.0500)
BSC
0.25 (0.0098)
0.10 (0.0040)
COPLANARITY
SEATING
0.10
PLANE
6.20 (0.2440)
5.80 (0.2284)
0.50 (0.0196)
ⴛ 45ⴗ
0.25 (0.0099)
8ⴗ
0.25 (0.0098) 0ⴗ 1.27 (0.0500)
0.41 (0.0160)
0.19 (0.0075)
0.0400 (1.02) MAX
0.0400 (1.02)
0.0100 (0.25)
COMPLIANT TO JEDEC STANDARDS MS-012AA
CONTROLLING DIMENSIONS ARE IN MILLIMETERS; INCH DIMENSIONS
(IN PARENTHESES) ARE ROUNDED-OFF MILLIMETER EQUIVALENTS FOR
REFERENCE ONLY AND ARE NOT APPROPRIATE FOR USE IN DESIGN
REV. E
0.1000 (2.54) BSC
0.1600 (4.06)
0.1400 (3.56)
5
1.75 (0.0688)
1.35 (0.0532)
0.51 (0.0201)
0.33 (0.0130)
0.2500 (6.35) MIN
0.0500 (1.27) MAX
0.3700 (9.40)
0.3350 (8.51)
0.3350 (8.51)
0.3050 (7.75)
4.00 (0.1574)
3.80 (0.1497)
8
0.1850 (4.70)
0.1650 (4.19)
0.5000 (12.70)
MIN
6
4
0.2000
(5.08)
BSC
3
7
2
0.0190 (0.48)
0.0160 (0.41)
0.1000
(2.54)
BSC
0.0210 (0.53)
0.0160 (0.41)
0.0450 (1.14)
0.0270 (0.69)
8
1
0.0340 (0.86)
0.0280 (0.71)
45 BSC
BASE & SEATING PLANE
COMPLIANT TO JEDEC STANDARDS MO-002AK
CONTROLLING DIMENSIONS ARE IN INCHES; MILLIMETERS DIMENSIONS
(IN PARENTHESES) ARE ROUNDED-OFF EQUIVALENTS FOR
REFERENCE ONLY AND ARE NOT APPROPRIATE FOR USE IN DESIGN
–13–
AD711
Revision History
Location
Page
10/02—Data Sheet changed from REV. D to REV. E.
Edits to ABSOLUTE MAXIMUM RATINGS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3
10/02—Data Sheet changed from REV. C to REV. D.
Edits to CONNECTION DIAGRAMS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1
Updated OUTLINE DIMENSIONS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13
5/02—Data Sheet changed from REV. B to REV. C.
Change from Small Outline Package (R-8) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13
Edits to ORDERING GUIDE . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3
Deleted METALLIZATION PHOTOGRAPH . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3
–14–
REV. E
–15–
–16–
PRINTED IN U.S.A.
C00832–0–10/02(E)