AD AD8036ACHIPS

FEATURES
Superb Clamping Characteristics
3 mV Clamp Error
1.5 ns Overdrive Recovery
Minimized Nonlinear Clamping Region
240 MHz Clamp Input Bandwidth
3.9 V Clamp Input Range
Wide Bandwidth
AD8036
AD8037
Small Signal
240 MHz 270 MHz
Large Signal (4 V p-p) 195 MHz 190 MHz
Good DC Characteristics
2 mV Offset
10 V/C Drift
Ultralow Distortion, Low Noise
–72 dBc typ @ 20 MHz
4.5 nV/√Hz Input Voltage Noise
High Speed
Slew Rate 1500 V/s
Settling 10 ns to 0.1%, 16 ns to 0.01%
3 V to 5 V Supply Operation
APPLICATIONS
ADC Buffer
IF/RF Signal Processing
High Quality Imaging
Broadcast Video Systems
Video Amplifier
Full Wave Rectifier
PRODUCT DESCRIPTION
The AD8036 and AD8037 are wide bandwidth, low distortion
clamping amplifiers. The AD8036 is unity gain stable. The
AD8037 is stable at a gain of two or greater. These devices
allow the designer to specify a high (VCH) and low (VCL) output
clamp voltage. The output signal will clamp at these specified
levels. Utilizing a unique patent pending CLAMPIN™ input
clamp architecture, the AD8036 and AD8037 offer a 10×
improvement in clamp performance compared to traditional
output clamping devices. In particular, clamp error is typically
3 mV or less and distortion in the clamp region is minimized.
This product can be used as a classical op amp or a clamp
amplifier where a high and low output voltage are specified.
The AD8036 and AD8037, which utilize a voltage feedback
architecture, meet the requirements of many applications which
previously depended on current feedback amplifiers. The AD8036
and AD8037 exhibit an exceptionally fast and accurate pulse
response (16 ns to 0.01%), extremely wide small-signal and
FUNCTIONAL BLOCK DIAGRAM
8-Lead Plastic DIP (N), Cerdip (Q),
and SO Packages
NC
1
–INPUT
AD8036/
AD8037
8
VH
2
7
+VS
+INPUT
3
6
OUTPUT
–VS
4
5
VL
(Top View)
NC = NO CONNECT
large-signal bandwidths and ultralow distortion. The AD8036
achieves –66 dBc at 20 MHz, and 240 MHz small-signal and
195 MHz large-signal bandwidths. The AD8036 and AD8037’s
recover from 2× clamp overdrive within 1.5 ns. These characteristics position the AD8036/AD8037 ideally for driving as well as
buffering flash and high resolution ADCs.
In addition to traditional output clamp amplifier applications,
the input clamp architecture supports the clamp levels as additional inputs to the amplifier. As such, in addition to static dc
clamp levels, signals with speeds up to 240 MHz can be applied
to the clamp pins. The clamp values can also be set to any value
within the output voltage range provided that VH is greater that
VL. Due to these clamp characteristics, the AD8036 and AD8037
can be used in nontraditional applications such as a full-wave
rectifier, a pulse generator, or an amplitude modulator. These
novel applications are only examples of some of the diverse
applications which can be designed with input clamps.
The AD8036 is offered in chips, industrial (–40°C to +85°C)
and military (–55°C to +125°C) package temperature ranges
and the AD8037 in industrial. Industrial versions are available
in plastic DIP and SOIC; MIL versions are packaged in cerdip.
4
AD8036
VH = 3V
3
OUTPUT VOLTAGE – Volts
a
Low Distortion, Wide Bandwidth
Voltage Feedback Clamp Amps
AD8036/AD8037
VH = 2V
2
VH = 1V
1
0
VL = –1V
–1
–2
VL = –2V
VL = –3V
–3
CLAMPIN is a trademark of Analog Devices, Inc.
–4
–4
REV. B
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
which may result from its use. No license is granted by implication or
otherwise under any patent or patent rights of Analog Devices.
–3
–2
–1
0
1
INPUT VOLTAGE – Volts
2
3
4
Figure 1. Clamp DC Accuracy vs. Input Voltage
One Technology Way, P.O. Box 9106, Norwood, MA 02062-9106, U.S.A.
Tel: 781/329-4700
World Wide Web Site: http://www.analog.com
Fax: 781/326-8703
© Analog Devices, Inc., 2000
AD8036/AD8037–SPECIFICATIONS
(V = 5 V; R = 100 ; A = +1 (AD8036); A = +2 (AD8037), V , V open, unless
S
LOAD
ELECTRICAL CHARACTERISTICS otherwise noted)
Parameter
DYNAMIC PERFORMANCE
Bandwidth (–3 dB)
Small Signal
Large Signal1
Bandwidth for 0.1 dB Flatness
Slew Rate, Average +/–
Rise/Fall Time
Settling Time
To 0.1%
To 0.01%
HARMONIC/NOISE PERFORMANCE
2nd Harmonic Distortion
3rd Harmonic Distortion
3rd Order Intercept
Noise Figure
Input Voltage Noise
Input Current Noise
Average Equivalent Integrated
Input Noise Voltage
Differential Gain Error (3.58 MHz)
Differential Phase Error (3.58 MHz)
Phase Nonlinearity
CLAMP PERFORMANCE
Clamp Voltage Range 2
Clamp Accuracy
Clamp Nonlinearity Range 3
Clamp Input Bias Current (V H or VL)
Clamp Input Bandwidth (–3 dB)
Clamp Overshoot
Overdrive Recovery
DC PERFORMANCE 4, RL = 150 Ω
Input Offset Voltage5
V
V
AD8036A
Min Typ Max
Conditions
AD8037A
Min Typ Max
Unit
MHz
MHz
240
195
200
160
130
1200
1.4
2.6
130
1100 1500
1.2
2.2
VOUT = 2 V Step
VOUT = 2 V Step
10
16
2 V p-p; 20 MHz, RL = 100 Ω
RL = 500 Ω
2 V p-p; 20 MHz, RL = 100 Ω
RL = 500 Ω
25 MHz
RS = 50 Ω
1 MHz to 200 MHz
1 MHz to 200 MHz
–59
–66
–68
–72
46
18
6.7
2.2
0.1 MHz to 200 MHz
RL = 150 Ω
RL = 150 Ω
DC to 100 MHz
95
0.05
0.02
1.1
VCH or VCL
2× Overdrive, VCH = +2 V, VCL = –2 V
TMIN–TMAX
8036, VH, L = ± 1 V; 8037, VH, L = ± 0.5 V
TMIN–TMAX
VCH or VCL = 2 V p-p
2× Overdrive, VCH or VCL = 2 V p-p
2× Overdrive
± 3.3
± 3.9
±3
100
± 40
150
240
1
1.5
2
± 10
4
Offset Voltage Drift
Input Bias Current
TMIN –TMAX
Input Offset Current
0.3
TMIN –TMAX
VCM = ± 2 V
VOUT = ± 2.5 V
TMIN –TMAX
66
48
40
INPUT CHARACTERISTICS
Input Resistance
Input Capacitance
Input Common-Mode Voltage Range
OUTPUT CHARACTERISTICS
Output Voltage Range, R L = 150 Ω
Output Current
Output Resistance
Short Circuit Current
POWER SUPPLY
Operating Range
Quiescent Current
Power Supply Rejection Ratio
L
150
VOUT ≤ 0.4 V p-p
8036, VOUT = 2.5 V p-p; 8037, V OUT = 3.5 V p-p 160
VOUT ≤ 0.4 V p-p
8036, RF = 140 Ω; 8037, RF = 274 Ω
900
VOUT = 4 V Step, 10–90%
VOUT = 0.5 V Step, 10–90%
VOUT = 4 V Step, 10–90%
TMIN –TMAX
Common-Mode Rejection Ratio
Open-Loop Gain
H
TMIN –TMAX
TMIN –TMAX
270
190
MHz
V/µs
ns
ns
10
16
–52
–59
–61
–65
–52
–72
–70
–80
41
14
4.5
2.1
60
0.02
0.02
1.1
0.09
0.04
± 10
± 20
± 60
± 80
5
–45
–65
–63
–73
0.04
0.04
± 3.3 ± 3.9
±3
± 10
± 20
100
± 50 ± 70
± 90
180 270
1
5
1.3
7
11
2
± 10
3
10
15
3
5
90
55
ns
ns
0.1
70
54
46
7
10
9
15
3
5
90
60
dBc
dBc
dBc
dBc
dBm
dB
nV√Hz
pA√Hz
µV rms
%
Degree
Degree
V
mV
mV
mV
µA
µA
MHz
%
ns
mV
mV
µV/°C
µA
µA
µA
µA
dB
dB
dB
500
1.2
± 2.5
500
1.2
± 2.5
kΩ
pF
V
± 3.2
± 3.9
70
0.3
240
± 3.2 ± 3.9
70
0.3
240
V
mA
Ω
mA
± 3.0
± 5.0
20.5
50
60
± 3.0 ± 5.0 ± 6.0
18.5 19.5
24
56
66
V
mA
mA
dB
± 6.0
21.5
25
NOTES
1
See Max Ratings and Theory of Operation sections of data sheet.
2
See Max Ratings.
3
Nonlinearity is defined as the voltage delta between the set input clamp voltage (VH or VL) and the voltage at which VOUT starts deviating from VIN (see Figure 73).
4
Measured at AV = 50.
5
Measured with respect to the inverting input.
Specifications subject to change without notice.
–2–
REV. B
AD8036/AD8037
ABSOLUTE MAXIMUM RATINGS 1
MAXIMUM POWER DISSIPATION
Supply Voltage . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12.6 V
Voltage Swing × Bandwidth Product . . . . . . . . . . . 350 V-MHz
|VH–VIN| . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ≤ 6.3 V
|VL–VIN| . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ≤ 6.3 V
Internal Power Dissipation2
Plastic DIP Package (N) . . . . . . . . . . . . . . . . . . . . 1.3 Watts
Small Outline Package (SO) . . . . . . . . . . . . . . . . . . 0.9 Watts
Input Voltage (Common Mode) . . . . . . . . . . . . . . . . . . . . ± VS
Differential Input Voltage . . . . . . . . . . . . . . . . . . . . . . . ± 1.2 V
Output Short Circuit Duration
. . . . . . . . . . . . . . . . . . . . . . Observe Power Derating Curves
Storage Temperature Range N, R . . . . . . . . . –65°C to +125°C
Operating Temperature Range (A Grade) . . . –40°C to +85°C
Lead Temperature Range (Soldering 10 sec) . . . . . . . . . 300°C
The maximum power that can be safely dissipated by these
devices is limited by the associated rise in junction temperature.
The maximum safe junction temperature for plastic encapsulated
devices is determined by the glass transition temperature of the
plastic, approximately 150°C. Exceeding this limit temporarily
may cause a shift in parametric performance due to a change
in the stresses exerted on the die by the package. Exceeding
a junction temperature of 175°C for an extended period can
result in device failure.
While the AD8036 and AD8037 are internally short circuit protected, this may not be sufficient to guarantee that the maximum junction temperature (150°C) is not exceeded under all
conditions. To ensure proper operation, it is necessary to observe
the maximum power derating curves.
NOTES
1
Stresses above those listed under Absolute Maximum Ratings may cause permanent damage to the device. This is a stress rating only; 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
Specification is for device in free air:
8-Lead Plastic DIP: θJA = 90°C/W
8-Lead SOIC: θJA = 155°C/W
8-Lead Cerdip: θJA = 110°C/W.
MAXIMUM POWER DISSIPATION – Watts
2.0
METALIZATION PHOTO
Dimensions shown in inches and (mm).
Connect Substrate to –V S.
–IN
VH
2
8
+VS
7
8-LEAD PLASTIC DIP
PACKAGE
TJ = +150C
1.5
1.0
8-LEAD SOIC
PACKAGE
0.5
0
–50 –40 –30 –20 –10 0 10 20 30 40 50 60
AMBIENT TEMPERATURE – C
0.046
(1.17)
6
70
80 90
Figure 2. Plot of Maximum Power Dissipation vs.
Temperature
OUT
ORDERING GUIDE
3
+IN
4
–VS
5
8036
VL
Model
AD8036
0.050 (1.27)
–IN
VH
+VS
2
8
7
0.046
(1.17)
6
3
+IN
4
–VS
5
VL
0.050 (1.27)
OUT
Temperature
Range
Package
Option
AD8036AN
AD8036AR
AD8036AR-REEL
AD8036AR-REEL7
AD8036ACHIPS
AD8036-EB
5962-9559701MPA
–40°C to +85°C
–40°C to +85°C
–40°C to +85°C
–40°C to +85°C
–40°C to +85°C
Plastic DIP
SOIC
13" Tape and Reel
7" Tape and Reel
Die
Evaluation Board
–55°C to +125°C Cerdip
N-8
SO-8
SO-8
SO-8
AD8037AN
AD8037AR
AD8037AR-REEL
AD8037AR-REEL7
AD8037ACHIPS
AD8037-EB
–40°C to +85°C
–40°C to +85°C
–40°C to +85°C
–40°C to +85°C
–40°C to +85°C
N-8
SO-8
SO-8
SO-8
Plastic DIP
SOIC
13" Tape and Reel
7" Tape and Reel
Die
Evaluation Board
Q-8
8037
AD8037
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 AD8036/AD8037 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. B
Package
Description
–3–
WARNING!
ESD SENSITIVE DEVICE
AD8036/AD8037
AD8036–Typical Characteristics
RF
RF
10F
+VS
PULSE
GENERATOR
10F
+VH
PULSE
GENERATOR
0.1F
T R /T F = 350ps
+VS
0.1F
0.1F
T R /T F = 350ps
130
AD8036
VIN
VOUT
0.1F
49.9
AD8036
130
VIN
RL = 100
49.9
10F
VL
TPC 1. Noninverting Configuration, G = +1
RL = 100
10F
0.1F
–VS
VOUT
0.1F
–VS
TPC 4. Noninverting Clamp Configuration, G = +1
TPC 5. Clamped Large Signal Transient Response (2×
Overdrive); VO = 2 V p-p, G = +1, RF = 140 Ω, VH = +1 V,
VL = –1 V
TPC 2. Large Signal Transient Response; VO = 4 V
p-p, G = +1, RF = 140 Ω
TPC 6. Clamped Small Signal Transient Response
(2 × Overdrive); VO = 400 mV p-p, G = +1, RF = 140 Ω,
VH = +0.2 V, VL = –0.2 V
TPC 3. Small Signal Transient Response; VO = 400 mV p-p,
G = +1, RF = 140 Ω
–4–
REV. B
AD8036/AD8037
AD8037–Typical Characteristics
RF
RF
PULSE
GENERATOR
10F
+VS
T R /T F = 350ps
PULSE
GENERATOR
T R /T F = 350ps
0.1F
AD8037
VIN
VOUT
0.1F
49.9
0.1F
0.1F
AD8037
100
VIN
RL = 100
VOUT
0.1F
49.9
10F
RL = 100
10F
0.1F
VL
–VS
–VS
TPC 10. Noninverting Clamp Configuration, G = +2
TPC 7. Noninverting Configuration, G = +2
TPC 11. Clamped Large Signal Transient Response
(2 × Overdrive); VO = 2 V p-p, G = +2, RF = RIN = 274
Ω, VH = +0.5 V, VL = –0.5 V
TPC 8. Large Signal Transient Response; VO = 4 V p-p,
G = +2, RF = RIN = 274 Ω
TPC 12. Clamped Small Signal Transient Response
(2 × Overdrive); VO = 400 mV p-p, G = +2, RF = RIN =
274 Ω, VH = +0.1 V, VL = –0.1 V
TPC 9. Small Signal Transient Response;
VO = 400 mV p-p, G = +2, RF = RIN = 274 Ω
REV. B
+VS
RIN
RIN
100
10F
+VH
–5–
AD8036/AD8037
AD8036–Typical Characteristics
2
400
140
GAIN – dB
–2
VO = 300mV p-p
VS = 5V
RL = 100
–3dB BANDWIDTH – MHz
0
–1
RF
200
1
102
49.9
–3
–4
–5
VS = 5V
RL = 100
GAIN = +1
350
130
AD8036
RL
49.9
N PACKAGE
300
R PACKAGE
250
–6
200
–7
–8
1M
10M
100M
FREQUENCY – Hz
20
1G
TPC 13. AD8036 Small Signal Frequency Response,
G = +1
0
VO = 300mV p-p
VS = 5V
RL = 100
–1
140
130
–0.4
–2
–5
–6
–0.7
–7
10M
100M
FREQUENCY – Hz
TPC 14. AD8036 0.1 dB Flatness, N Package (for R
Package Add 20 Ω to RF)
100
2
80
80
1
70
60
20
40
0
GAIN
–1
GAIN – dB
50
–2
–20
20
–40
10
–60
0
–80
–6
–100
–7
100k
1M
10M
FREQUENCY – Hz
100M
VS = 5V
VO = 300mV p-p
RL = 100
140
–3
30
–10
1G
0
PHASE MARGIN – Degrees
40
10M
100M
FREQUENCY – Hz
TPC 17. AD8036 Large Signal Frequency Response,
G = +1
90
PHASE
50
RF = 50
TO
250
BY
50
–8
1M
1G
60
VS = 5V
VO = 2.5V p-p
RL = 100
–4
–0.6
–0.8
1M
250
–3
–0.5
OPEN -LOOP GAIN – dB
240
0
OUTPUT – dB
GAIN – dB
1
150
–0.1
–20
10k
220
2
158
0.1
–0.3
60
80 100 120 140 160 180 200
VALUE OF FEEDBACK RESISTOR (RF) – TPC 16. AD8036 Small Signal –3 dB Bandwidth vs. RF
0.2
–0.2
40
–4
–120
1G
–8
100k
TPC 15. AD8036 Open-Loop Gain and Phase Margin vs.
Frequency, RL = 100 Ω
(VO)
AD8036
–5
1V
100
VH
VL (VIN)
1M
10M
FREQUENCY – Hz
100M
1G
TPC 18. AD8036 Clamp Input Bandwidth, VH, VL
–6–
REV. B
AD8036/AD8037
0.06
DIFF GAIN – %
–50
VO = 2V p-p
VS = 5V
RL = 500
G = +1
–70
2ND HARMONIC
–90
3RD HARMONIC
–110
–130
10k
0.04
0.02
0.00
–0.02
–0.04
–0.06
DIFF PHASE – Degrees
HARMONIC DISTORTION – dBc
–30
100k
1M
FREQUENCY – Hz
10M
2nd
3rd
4th
5th
6th
7th
8th
9th 10th 11th
1st
2nd
3rd
4th
5th
6th
7th
8th
9th 10th 11th
0.04
0.02
0.00
–0.02
–0.04
100M
TPC 19. AD8036 Harmonic Distortion vs. Frequency,
RL = 500 Ω
1st
TPC 22. AD8036 Differential Gain and Phase Error,
G = +1, RL = 150 Ω, F = 3.58 MHz
–50
0.05
VO = 2V p-p
VS = 5V
RL = 100
G = +1
0.04
0.03
0.02
2ND HARMONIC
–70
ERROR – %
HARMONIC DISTORTION – dBc
–30
–90
0.01
0
–0.01
3RD HARMONIC
–0.02
–110
–0.03
–0.04
–130
10k
–0.05
100k
1M
FREQUENCY – Hz
10M
100M
0
TPC 20. AD8036 Harmonic Distortion vs. Frequency,
RL = 100 Ω
5
10 15 20 25 30
SETTLING TIME – ns
35
40
45
TPC 23. AD8036 Short-Term Settling Time to 0.01%, 2 V
Step, G = +1, RL = 100 Ω
60
0.4
0.3
0.2
0.1
ERROR – %
INTERCEPT – +dBm
50
40
0
–0.1
–0.2
–0.3
30
–0.4
–0.5
20
10
–0.6
20
40
FREQUENCY – MHz
60
80
100
0
TPC 21. AD8036 Third Order Intercept vs. Frequency
REV. B
2
4
6
8 10 12 14
SETTLING TIME - s
16
18
TPC 24. AD8036 Long-Term Settling Time, 2 V Step,
G = +1, RL = 100 Ω
–7–
AD8036/AD8037
AD8037–Typical Characteristics
8
475
7
374
VS = 5V
RL = 100
GAIN = +2
350
GAIN – dB
5
VO = 300mV p-p
VS = 5V
RL = 100
4
–3dB BANDWIDTH – MHz
6
274
174
3
2
1
RIN
100
RF
AD8037
RL
300
49.9
250
R PACKAGE
N PACKAGE
200
0
–1
150
–2
1M
10M
100M
FREQUENCY – Hz
1G
100
TPC 25. AD8037 Small Signal Frequency Response,
G = +2
274
VO = 3.00mV p-p
VS = 5V
RL = 100
6
5
249
224
4
GAIN – dB
GAIN – dB
550
RF = 475
7
–0.3
–0.4
1
0
–0.7
–1
RF = 75
TO
475
BY
100
–2
1M
1G
TPC 26. AD8037 0.1 dB Flatness, N Package
(for R Package Add 20 Ω to RF)
RF = 75
2
–0.6
10M
100M
FREQUENCY – Hz
VO = 3.5 V p-p
VS = 5V
RL = 100
3
–0.5
–0.8
1M
10M
100M
FREQUENCY – Hz
1G
TPC 29. AD8037 Large Signal Frequency Response, G = +2
8
65
60
55
50
7
100
PHASE
6
50
35
0
30
25
20
–50
GAIN
15
10
–100
5
0
–150
–5
–10
–200
100k
1M
10M
FREQUENCY – Hz
100M
5
GAIN – dB
45
40
PHASE MARGIN – Degrees
OPEN -LOOP GAIN – dB
500
8
0
–15
10k
250 300 350 400 450
VALUE OF RF,RIN – 301
0.1
–0.2
200
TPC 28. AD8037 Small Signal –3 dB Bandwidth vs. RF, RIN
0.2
–0.1
150
4
VS = 5V
VO = 300mV p-p
RL = 100
274
3
2
274
0
1V
–2
100k
100
VH
VL (VIN)
–1
–250
1G
(VO)
AD8037
1
1M
10M
FREQUENCY – Hz
100M
1G
TPC 30. AD8037 Clamp Input Bandwidth, VH, VL
TPC 27. AD8037 Open-Loop Gain and Phase Margin
vs. Frequency, RL = 100 Ω
–8–
REV. B
AD8036/AD8037
0.03
DIFF GAIN – %
–50
VO = 2V p-p
VS = 5V
RL = 500
G = +2
–70
0.02
0.01
0.00
–0.01
–0.02
–0.03
2ND HARMONIC
1st
DIFF PHASE – Degrees
HARMONIC DISTORTION – dBc
–30
–90
3RD HARMONIC
–110
–130
10k
100k
1M
FREQUENCY – Hz
5th
6th
7th
8th
9th 10th 11th
2nd
3rd
4th
5th
6th
7th
8th
9th 10th 11th
0.01
0.00
–0.01
–0.02
–0.03
TPC 34. AD8037 Differential Gain and Phase Error
G = +2, RL = 150 Ω, F = 3.58 MHz
–30
–0.05
–0.04
VO = 2V p-p
VS = 5V
RL = 100
G = +2
–0.03
2ND HARMONIC
–0.02
ERROR – %
HARMONIC DISTORTION – dBc
4th
0.02
1st
TPC 31. AD8037 Harmonic Distortion vs. Frequency,
RL = 500 Ω
–50
3rd
0.03
100M
10M
2nd
–70
–90
3RD HARMONIC
–0.01
0
–0.01
–0.02
–0.03
–110
–0.04
–0.05
–130
10k
100k
1M
FREQUENCY – Hz
0
100M
10M
5
10 15 20 25 30
SETTLING TIME – ns
35
40
45
TPC 35. AD8037 Short-Term Settling Time to 0.01%,
2 V Step, G = +2, RL = 100 Ω
TPC 32. AD8037 Harmonic Distortion vs. Frequency,
RL = 100 Ω
60
0.4
0.3
0.2
0.1
ERROR – %
INTERCEPT – +dBm
50
40
0
–0.1
–0.2
–0.3
30
–0.4
–0.5
–0.6
20
10
20
40
FREQUENCY – MHz
60
80
0
100
4
6
8 10 12 14
SETTLING TIME – s
16
18
TPC 36. AD8037 Long-Term Settling Time 2 V Step,
RL = 100 Ω
TPC 33. AD8037 Third Order Intercept vs. Frequency
REV. B
2
–9–
AD8036/AD8037–Typical Characteristics
17
28
15
INPUT NOISE VOLTAGE – nV/ Hz
INPUT NOISE VOLTAGE – nV/ Hz
32
VS = 5V
24
20
16
12
VS = 5V
13
11
9
7
8
5
4
10
100
1k
FREQUENCY – Hz
10k
3
10
100k
TPC 37. AD8036 Noise vs. Frequency
–PSRR
65
60
55
50
45
+PSRR
40
35
30
25
20
15
10
5
0
10k
100k
1M
10M
FREQUENCY – Hz
100M
1G
80
75
70
65
60
55
50
45
40
35
30
25
20
15
10
5
0
10k
TPC 38. AD8036 PSRR vs. Frequency
10k
100k
–PSRR
+PSRR
100k
1M
10M
FREQUENCY – Hz
100M
1G
TPC 41. AD8037 PSRR vs. Frequency
100
100
VS = 5V
VCM = 1V
RL = 100
90
VS = 5V
VCM = 1V
RL = 100
90
80
CMRR – dB
80
CMRR – dB
1k
FREQUENCY – Hz
TPC 40. AD8037 Noise vs. Frequency
PSRR – dB
PSRR – dB
80
75
70
100
70
60
70
60
50
50
40
40
30
30
20
100k
1M
10M
FREQUENCY – Hz
100M
20
100k
1G
TPC 39. AD8036 CMRR vs. Frequency
1M
10M
FREQUENCY – Hz
100M
1G
TPC 42. AD8037 CMRR vs. Frequency
–10–
REV. B
AD8036/AD8037
1400
1k
1300
VS = 5V
G = +1
1200
OPEN -LOOP GAIN – V/ V
100
ROUT – 10
1
1100
AD8037
1000
+AOL
900
–AOL
800
700
600
0.1
500
+AOL
AD8036
–AOL
0.01
0.1M
1.0M
10M
FREQUENCY – Hz
100M
400
–60
300M
–40
–20
0
20
40
60
80
100
120
140
JUNCTION TEMPERATURE – C
TPC 43. AD8036 Output Resistance vs. Frequency
TPC 46. Open-Loop Gain vs. Temperature
1k
74
–PSRR
72
VS = 5V
G = +2
100
AD8037
70
+PSRR
PSRR – dB
ROUT – 10
1
68
AD8037
66
64
–PSRR
AD8036
+PSRR
0.1
62
AD8036
0.01
0.1M
1.0M
10M
FREQUENCY – Hz
100M
60
–60
300M
TPC 44. AD8037 Output Resistance vs. Frequency
120
140
VCM = 2V
RL=150
+VOUT
95
4.0
94
–VOUT
3.9
CMRR – dB
OUTPUT SWING – Volts
0
20
40
60
80 100
JUNCTION TEMPERATURE – C
96
4.1
3.8
3.7
3.6
3.5
–VOUT
–40
–20
0
20
40
60
80
100
JUNCTION TEMPERATURE – C
93
92
91
90
+VOUT
120
RL= 50
89
140
88
15
TPC 45. AD8036/AD8037 Output Swing vs. Temperature
REV. B
–20
TPC 47. PSRR vs. Temperature
4.2
3.4
–60
–40
25
35
45
55
65
75
JUNCTION TEMPERATURE – C
85
95
TPC 48. AD8036/AD8037 CMRR vs. Temperature
–11–
AD8036/AD8037–Typical Characteristics
270
24
SHORT CIRCUIT CURRENT – mA
23
SUPPLY CURRENT – mA
AD8036, VS = 6V
22
AD8037, VS = 6V
21
AD8036, VS = 5V
20
AD8037, VS = 5V
19
18
260
AD8036
250
AD8037
AD8037
SINK
240
AD8036
230
SOURCE
220
210
17
–60
–40
–20
0
20
40
60
80 100
JUNCTION TEMPERATURE – C
120
200
–60
140
–40
–20
0
20
40
60
80 100
JUNCTION TEMPERATURE – C
120
140
TPC 52. Short Circuit Current vs. Temperature
TPC 49. Supply Current vs. Temperature
–2.50
4.5
VS = 6V
–IB
4.0
INPUT BIAS CURRENT – A
INPUT OFFSET VOLTAGE – mV
–2.25
–2.00
VS = 6V
AD8037
–1.75
–1.50
VS = 5V
VS = 5V
–1.25
AD8036
–1.00
+IB
3.5
–IB
3.0
+IB
2.5
–40
–20
0
20
40
60
80 100
JUNCTION TEMPERATURE – C
120
1.5
–60
140
TPC 50. Input Offset Voltage vs. Temperature
44
0
20
40
60
80
100
JUNCTION TEMPERATURE – C
120
140
3 WAFER LOTS
COUNT = 853
40
36
32
FREQ. DIST
32
24
COUNT
28
COUNT
–20
48
3 WAFER LOTS
COUNT = 632
36
FREQ. DIST
20
16
28
24
20
16
12
12
8
8
4
4
0
–6
–40
TPC 53. Input Bias Current vs. Temperature
44
40
AD8037
2.0
–0.75
–0.50
–60
AD8036
–5
–4
–3
–2
–1
0
1
INPUT OFFSET VOLTAGE – mV
2
3
0
–4.5
4
TPC 51. AD8036 Input Offset Voltage Distribution
–4.0
–3.5
–3.0 –2.5 –2.0 –1.5 –1.0 –0.5
INPUT OFFSET VOLTAGE – mV
0
0.5
TPC 54. AD8037 Input Offset Voltage Distribution
–12–
REV. B
Clamp Characteristics–AD8036/AD8037
20
–80
VCL =
–3V
10
VCL =
–2V
VCL =
–1V
–75
AD8036, ACL = +1
AD8037, ACL = +2
HARMONIC DISTORTION – dBc
INPUT ERROR VOLTAGE – mV
15
5
0
AD8036
–5
AD8037
–10
VCH =
+1V
–15
VCH =
+2V
VCH =
+3V
AD8037 3RD
HARMONIC
–65
–60
AD8037 2ND
HARMONIC
–55
–2
–1
0
1
OUTPUT VOLTAGE – Volts
2
AD8036 2ND
HARMONIC
–45
AD8036 AD8037
–40
VH
VL
G
–30
0.6
3
TPC 55. Input Error Voltage vs. Clamped Output Voltage
+1V
–1V
+1V
+0.5V
–0.5V
+2V
0.65
0.7
0.75
0.8
0.85
0.9
0.95
ABSOLUTE VALUE OF OUTPUT VOLTAGE – Volts
1.0
TPC 58. Harmonic Distortion as Output Approaches
Clamp Voltage; VO = 2 V p-p, RL = 100 , f = 20 MHz
20
80
CLAMP INPUT BIAS CURRENT – A
VH = + 1V
VL = – 1V
15
10
5
0
–5
–10
–15
60
POSITIVE IBH, IBL DENOTES
CURRENT FLOW INTO
CLAMP INPUTS VH, VL
40
20
IBL
0
IBH
–20
–40
–60
–20
–1.0
–0.8
–0.6
–0.4 –0.2 0.0
0.2 0.4
INPUT VOLTAGE AV – Volts
0.6
0.8
–80
–5
1.0
TPC 56. AD8036/AD8037 Nonlinearity Near Clamp Voltage
–4
–3
–2
–1
0
1
2
3
INPUT CLAMP VOLTAGE (VH ,VL) – Volts
4
5
TPC 59. AD8036/AD8037 Clamp Input Bias Current vs.
Input Clamp Voltage
+2V
+2V
+1V
+1V
0V
0V
REF
REF
TPC 60. AD8037 Clamp Overdrive (2 ×) Recovery
TPC 57. AD8036 Clamp Overdrive (2 ×) Recovery
REV. B
AD8036 3RD
HARMONIC
–50
–35
–20
–3
NONLINEARITY – mV
–70
–13–
0.5
0.5
0.4
0.4
0.3
0.3
0.2
0.2
0.1
ERROR – %
ERROR – %
AD8036/AD8037–Clamp Characteristics
0
–0.1
–0.2
–0.3
–0.3
–0.4
–0.4
–0.5
0
10
20 30 40 50 60
SETTLING TIME – ns
70
80
90
0
TPC 61. AD8036 Clamp Settling (0.1%), VH = +1 V,
VL = –1 V, 2 × Overdrive
10
20 30 40 50 60
SETTLING TIME – ns
70
80
90
TPC 64. AD8037 Clamp Settling (0.1%), VH = +0.5 V,
VL = –0.5 V, 2 × Overdrive
0.5
0.5
0.4
0.4
0.3
0.3
0.2
0.2
ERROR – %
ERROR – %
0
–0.1
–0.2
–0.5
0.1
0
–0.1
0.1
0
–0.1
–0.2
–0.2
–0.3
–0.3
–0.4
–0.4
–0.5
–0.5
0
5 10 15 20 25
SETTLING TIME – ns
30
35
0
40
TPC 62. AD8036 Clamp Recovery Settling Time (High),
from +2 × Overdrive to 0 V
5 10 15 20 25
SETTLING TIME – ns
30
35
40
TPC 65. AD8037 Clamp Recovery Settling Time (High),
from +2 × Overdrive to 0 V
0.5
0.5
0.4
0.4
0.3
0.3
0.2
0.2
ERROR – %
ERROR – %
0.1
0.1
0
–0.1
0.1
0
–0.1
–0.2
–0.2
–0.3
–0.3
–0.4
–0.4
–0.5
–0.5
0
5
10 15 20 25
SETTLING TIME – ns
30
35
40
0
TPC 63. AD8036 Clamp Recovery Settling Time (Low),
from –2 × Overdrive to 0 V
5 10 15 20 25
SETTLING TIME – ns
30
35
40
TPC 66. AD8037 Clamp Recovery Settling Time (Low),
from –2 × Overdrive to 0 V
–14–
REV. B
AD8036/AD8037
This estimation loses accuracy for gains of +2/–1 or lower due
to the amplifier’s damping factor. For these “low gain” cases,
the bandwidth will actually extend beyond the calculated value
(see Closed-Loop BW plots, TPCs 13 and 25).
THEORY OF OPERATION
General
The AD8036 and AD8037 are wide bandwidth, voltage feedback
clamp amplifiers. Since their open-loop frequency response follows the conventional 6 dB/octave roll-off, their gain bandwidth
product is basically constant. Increasing their closed-loop gain
results in a corresponding decrease in small signal bandwidth. This
can be observed by noting the bandwidth specification, between
the AD8036 (gain of 1) and AD8037 (gain of 2). The AD8036/
AD8037 typically maintain 65 degrees of phase margin. This
high margin minimizes the effects of signal and noise peaking.
Pulse Response
While the AD8036 and AD8037 can be used in either an inverting or noninverting configuration, the clamp function will only
work in the noninverting mode. As such, this section shows connections only in the noninverting configuration. Applications
that require an inverting configuration will be discussed in the
Applications section. In applications that do not require clamping, Pins 5 and 8 (respectively VL and VH) may be left floating.
See Input Clamp Amp Operation and Applications sections
otherwise.
Feedback Resistor Choice
The value of the feedback resistor is critical for optimum performance on the AD8036 (gain +1) and less critical as the gain
increases. Therefore, this section is specifically targeted at
the AD8036.
Unlike a traditional voltage feedback amplifier, where the slew
speed is dictated by its front end dc quiescent current and gain
bandwidth product, the AD8036 and AD8037 provide “on
demand” current that increases proportionally to the input
“step” signal amplitude. This results in slew rates (1200 V/µs)
comparable to wideband current feedback designs. This, combined with relatively low input noise current (2.1 pA/√Hz), gives
the AD8036 and AD8037 the best attributes of both voltage and
current feedback amplifiers.
Large Signal Performance
The outstanding large signal operation of the AD8036 and
AD8037 is due to a unique, proprietary design architecture.
In order to maintain this level of performance, the maximum
350 V-MHz product must be observed, (e.g., @ 100 MHz,
VO ≤ 3.5 V p-p).
Power Supply and Input Clamp Bypassing
At minimum stable gain (+1), the AD8036 provides optimum
dynamic performance with RF = 140 Ω. This resistor acts only
as a parasitic suppressor against damped RF oscillations that
can occur due to lead (input, feedback) inductance and parasitic
capacitance. This value of RF provides the best combination of
wide bandwidth, low parasitic peaking, and fast settling time.
Adequate power supply bypassing can be critical when optimizing the performance of a high frequency circuit. Inductance in
the power supply leads can form resonant circuits that produce
peaking in the amplifier’s response. In addition, if large current
transients must be delivered to the load, then bypass capacitors
(typically greater than 1 µF) will be required to provide the best
settling time and lowest distortion. A parallel combination of at
least 4.7 µF, and between 0.1 µF and 0.01 µF, is recommended.
Some brands of electrolytic capacitors will require a small series
damping resistor ≈4.7 Ω for optimum results.
In fact, for the same reasons, a 100–130 Ω resistor should be
placed in series with the positive input for other AD8036 noninverting configurations. The correct connection is shown in
Figure 3.
When the AD8036 and AD8037 are used in clamping mode,
and a dc voltage is connected to clamp inputs VH and VL, a 0.1 µF
bypassing capacitor is required between each input pin and
ground in order to maintain stability.
Driving Capacitive Loads
+VS
10F
R
G = 1+ F
RG
VH
0.1F
100 - 130
VIN
AD8036/
AD8037
RTERM
VOUT
0.1F
10F
VL
RF
The AD8036 and AD8037 were designed primarily to drive
nonreactive loads. If driving loads with a capacitive component is desired, the best frequency response is obtained by
the addition of a small series resistance as shown in Figure 4.
The accompanying graph shows the optimum value for RSERIES
vs. capacitive load. It is worth noting that the frequency response
of the circuit when driving large capacitive loads will be dominated by the passive roll-off of RSERIES and CL. For capacitive
loads of 6 pF or less, no RSERIES is necessary.
–VS
RF
RG
RIN
Figure 3. Noninverting Operation
RIN
For general voltage gain applications, the amplifier bandwidth
can be closely estimated as:
f 3 dB ≅
REV. B
ωO
  R 
2π 1+  F  
  RG  
AD8036/
AD8037
RSERIES
RL
1k
Figure 4. Driving Capacitive Loads
–15–
CL
AD8036/AD8037
Operation of the AD8036 for negative input voltages and negative clamp levels on VL is similar, with comparator CL controlling S1. Since the comparators see the voltage on the +VIN pin
as their common reference level, then the voltage VH and VL are
defined as “High” or “Low” with respect to +VIN. For example,
if VIN is set to zero volts, VH is open, and VL is +1 V, comparator CL will switch S1 to “C,” so the AD8036 will buffer the
voltage on VL and ignore +VIN.
40
R SERIES – 30
The performance of the AD8036 and AD8037 closely matches
the ideal just described. The comparator’s threshold extends
from 60 mV inside the clamp window defined by the voltages on
VL and VH to 60 mV beyond the window’s edge. Switch S1 is
implemented with current steering, so that A1’s +input makes a
continuous transition from say, VIN to VH as the input voltage
traverses the comparator’s input threshold from 0.9 V to 1.0 V
for VH = 1.0 V.
20
10
0
5
10
15
20
25
CL– pF
Figure 5. Recommended RSERIES vs. Capacitive Load
The practical effect of these nonidealities is to soften the transition
from amplification to clamping modes, without compromising
the absolute clamp limit set by the CLAMPIN circuit. Figure 7
is a graph of VOUT vs. VIN for the AD8036 and a typical output
clamp amplifier. Both amplifiers are set for G = +1 and VH = 1 V.
INPUT CLAMPING AMPLIFIER OPERATION
The key to the AD8036 and AD8037’s fast, accurate clamp and
amplifier performance is their unique patent pending CLAMPIN
input clamp architecture. This new design reduces clamp errors
by more than 10× over previous output clamp based circuits, as
well as substantially increasing the bandwidth, precision and
versatility of the clamp inputs.
Figure 6 is an idealized block diagram of the AD8036 connected
as a unity gain voltage follower. The primary signal path comprises A1 (a 1200 V/µs, 240 MHz high voltage gain, differential
to single-ended amplifier) and A2 (a G = +1 high current gain
output buffer). The AD8037 differs from the AD8036 only in
that A1 is optimized for closed-loop gains of two or greater.
The CLAMPIN section is comprised of comparators CH and
CL, which drive switch S1 through a decoder. The unity-gain
buffers in series with +VIN, VH, and VL inputs isolate the input
pins from the comparators and S1 without reducing bandwidth
or precision.
The worst case error between VOUT (ideally clamped) and VOUT
(actual) is typically 18 mV times the amplifier closed-loop gain.
This occurs when VIN equals VH (or VL). As VIN goes above
and/or below this limit, VOUT will settle to within 5 mV of the
ideal value.
In contrast, the output clamp amplifier’s transfer curve typically
will show some compression starting at an input of 0.8 V, and
can have an output voltage as far as 200 mV over the clamp limit.
In addition, since the output clamp in effect causes the amplifier to operate open loop in clamp mode, the amplifier’s output impedance will increase, potentially causing additional errors.
The AD8036’s and AD8037’s CLAMPIN input clamp architecture works only for noninverting or follower applications and,
since it operates on the input, the clamp voltage levels VH and
VL, and input error limits will be multiplied by the amplifier’s
The two comparators have about the same bandwidth as A1
(240 MHz), so they can keep up with signals within the useful
bandwidth of the AD8036. To illustrate the operation of the
CLAMPIN circuit, consider the case where VH is referenced to
1 V, VL is open, and the AD8036 is set for a gain of +1, by connecting its output back to its inverting input through the recommended 140 Ω feedback resistor. Note that the main signal path
always operates closed loop, since the CLAMPIN circuit only
affects A1’s noninverting input.
RF
140
–VIN
+VIN
A1
A
+1
A2
+1
VOUT
S1
If a 0 V to 2 V voltage ramp is applied to the AD8036’s +VIN
for the connection just described, VOUT should track +VIN
perfectly up to 1 V, then should limit at exactly 1 V as +VIN
continues to 2 V.
VH
+1
VL
+1
B
C
S1
CH
VIN > VH
A B C
0 1 0
VL ≤ VIN ≤ VH 1 0 0
In practice, the AD8036 comes close to this ideal behavior. As
the +VIN input voltage ramps from zero to 1 V, the output of the
high limit comparator CH starts in the off state, as does the output of CL. When +VIN just exceeds VIN (ideally, by say 1 µV,
practically by about 18 mV), CH changes state, switching S1
from “A” to “B” reference level. Since the + input of A1 is now
connected to VH, further increases in +VIN have no effect on the
AD8036’s output voltage. In short, the AD8036 is now operating as a unity-gain buffer for the VH input, as any variation in
VH, for VH > 1 V, will be faithfully reproduced at VOUT.
–16–
VIN < VL
0 0 1
CL
Figure 6. AD8036/AD8037 Clamp Amp System
REV. B
AD8036/AD8037
closed-loop gain at the output. For instance, to set an output
limit of ± 1 V for an AD8037 operating at a gain of 3.0, VH and
VL would need to be set to +0.333 V and –0.333 V, respectively.
The only restriction on using the AD8036’s and AD8037’s
+VIN, VL, VH pins as inputs is that the maximum voltage difference between +VIN and VH or VL should not exceed 6.3 V, and
all three voltages be within the supply voltage range. For example,
if VL is set at –3 V, then VIN should not exceed +3.3 V.
Clamping with Gain
Figure 9 shows an AD8037 configured for a noninverting gain
of two. The AD8037 is used in this circuit since it is compensated for gains of two or greater and provides greater bandwidth.
In this case, the high clamping level at the output will occur at
VH
0.1F
+5V
0.1F
1.6
10F
130
VIN
VH
AD8036
OUTPUT VOLTAGE – VOUT
1.4
VOUT
VL
0.1F
1.2
10F
0.1F
CLAMP ERROR – 25mV
AD8036
–5V
CLAMP ERROR – >200mV
OUTPUT CLAMP
RF
140
VL
1.0
AD8036
0.6
0.6
Figure 8. Unity Gain Noninverting Clamp
OUTPUT CLAMP AMP
0.8
0.8
1.0
1.2
1.4
1.6
INPUT VOLTAGE – +VIN
1.8
2 × VH and the low clamping level at the output will be 2 × VL.
The equations governing the output clamp levels in circuits configured for noninverting gain are:
2.0
VCH = G × VH
VCL = G × VL
Figure 7. Output Clamp Error vs. Input Clamp Error
where:
AD8036/AD8037 APPLICATIONS
The AD8036 and AD8037 use a unique input clamping circuit
to perform the clamping function. As a result, they provide the
clamping function better than traditional output clamping
devices and provide additional flexibility to perform other
unique applications.
VCH is the high output clamping level
VCL is the low output clamping level
G is the gain of the amplifier configuration
VH is the high input clamping level (Pin 8)
VL is the low input clamping level (Pin 5)
*Amplifier offset is assumed to be zero.
VH
There are, however, some restrictions on circuit configurations;
and some calculations need to be performed in order to figure
the clamping level, as a result of clamping being performed at
the input stage.
0.1F
+5V
0.1F
10F
100
VIN
The major restriction on the clamping feature of the AD8036/
AD8037 is that clamping occurs only when using the amplifiers
in the noninverting mode. To clamp in an inverting circuit, an
additional inverting gain stage is required. Another restriction is
that VH be greater than VL, and that each be within the output
voltage range of the amplifier (± 3.9 V). VH can go below ground
and VL can go above ground as long as VH is kept higher than VL.
VH
49.9
AD8037
VOUT
VL
0.1F
10F
0.1F
–5V
RG
274
VL
RF
274
Unity Gain Clamping
The simplest circuit for calculating the clamp levels is a unity
gain follower as shown in Figure 8. In this case, the AD8036
should be used since it is compensated for noninverting unity gain.
Figure 9. Gain of Two Noninverting Clamp
This circuit will clamp at an upper voltage set by VH (the voltage
applied to Pin 8) and a lower voltage set by VL (the voltage
applied to Pin 5).
REV. B
–17–
AD8036/AD8037
+5V
806
+5V
0.1F
100
+5V
0.1F
–0.5V to +0.5V
10µF
0.1F
AD780
2.5V
49.9
–2V to 0V
AD8037
0.1F
100
R1
499
49.9
VIN = –2V TO 0V
CLAMPING
RANGE
–2.1V to +0.1V
VL
0.1F
806
1N5712
AD9002
VH
R3
750
10F
100
VIN
10F
SUBSTRATE
DIODE
–5V
0.1F
0.1F
R2
301
–5V
–5.2V
Figure 10. Gain of Two, Noninverting with Offset AD8037 Driving an AD9002—8-Bit, 125 MSPS A/D Converter
it goes no more than 100 mV outside of this range in either direction. Thus, the high clamping level should be set at +0.1 V
and the low clamping level should be set at –2.1 V as seen at the
input of the AD9002 (output of AD8037).
Clamping with an Offset
Some op amp circuits are required to operate with an offset
voltage. These are generally configured in the inverting mode
where the offset voltage can be summed in as one of the inputs.
Since AD8036/AD8037 clamping does not function in the inverting mode, it is not possible to clamp with this configuration.
Because the clamping is done at the input stage of the AD8037,
the clamping level as seen at the output is affected by not only
the gain of the circuit as previously described, but also by the
offset. Thus, in order to obtain the desired clamp levels, VH
must be biased at +0.55 V while VL must be biased at –0.55 V.
Figure 10 shows a noninverting configuration of an AD8037
that provides clamping and also has an offset. The circuit shows
the AD8037 as a driver for an AD9002, an 8-bit, 125 MSPS
A/D converter and illustrates some of the considerations for using an AD8037 with offset and clamping.
The clamping levels as seen at the output can be calculated by
the following:
The analog input range of the AD9002 is from ground to –2 V.
The input should not go more than 0.5 V outside this range in
order to prevent disruptions to the internal workings of the A/D
and to avoid drawing excess current. These requirements make
the AD8037 a prime candidate for signal conditioning.
VCH = VOFF + G × VH
VCL = VOFF + G × VL
Where VOFF is the offset voltage that appears at the output.
The resistors used to generate the voltages for VH and VL should
be kept to a minimum in order to reduce errors due to clamp
bias current. This current is dependent on VH and VL (see TPC
59) and will create a voltage drop across whatever resistance is
in series with each clamp input. This extra error voltage is
multiplied by the closed-loop gain of the amplifier and can be
substantial, especially in high closed-loop gain configurations.
A 0.1 µF bypass capacitor should be placed between input
clamp pins VH and VL and ground to ensure stable operation.
When an offset is added to a noninverting op amp circuit, it is
fed in through a resistor to the inverting input. The result is that
the op amp must now operate at a closed-loop gain greater than
unity. For this circuit a gain of two was chosen which allows the
use of the AD8037. The feedback resistor, R2, is set at 301 Ω
for optimum performance of the AD8037 at a gain of two.
There is an interaction between the offset and the gain, so some
calculations must be performed to arrive at the proper values for
R1 and R3. For a gain of two the parallel combination of resistors R1 and R3 must be equal to the feedback resistor R2. Thus
The 1N5712 Schottky diode is used for protection from forward
biasing the substrate diode in the AD9002 during power-up
transients.
R1 × R3/R1 + R3 = R2 = 301 Ω
Programmable Pulse Generator
The reference used to provide the offset is the AD780 whose
output is 2.5 V. This must be divided down to provide the 1 V
offset desired. Thus
The AD8036/AD8037’s clamp output can be set accurately and
has a well controlled flat level. This along with wide bandwidth
and high slew rate make them very well suited for programmable
level pulse generators.
2.5 V × R1/(R1 + R3) = 1 V
When the two equations are solved simultaneously we get R1 =
499 Ω and R3 = 750 Ω (using closest 1% resistor values in all
cases). This positive 1 V offset at the input translates to a –1 V
offset at the output.
The usable input signal swing of the AD9002 is 2 V p-p. This is
centered about the –1 V offset making the usable signal range
from 0 V to –2 V. It is desirable to clamp the input signal so that
Figure 11 is a schematic for a pulse generator that can directly
accept TTL generated timing signals for its input and generate
pulses at the output up to 24 V p-p with 2500 V/µs slew rate.
The output levels can be programmed to anywhere in the range
–12 V to +12 V.
–18–
REV. B
AD8036/AD8037
VH
0.1F
+5V
+15V
0.1F
200
10F
100
TTLIN
VH
1.3k
0.1F
100
AD8037
VL
10F
VL 10
PULSE
OUT
AD811
–15V
0.1F
VH 10
10F
0.1F
0.1F
–5V
VL
–15V
274
10F
604
150
274
Figure 11. Programmable Pulse Generator
The circuit uses an AD8037 operating at a gain of two with an
AD811 to boost the output to the ± 12 V range. The AD811 was
chosen for its ability to operate with ± 15 V supplies and its high
slew rate.
The circuit is configured as an inverting amplifier with a gain
of one. The input drives the inverting amplifier and also directly
drives VL, the lower level clamping input. The high level clamping input, VH, is left floating and plays no role in this circuit.
R1 and R2 act as a level shifter to make the TTL signal levels be
approximately symmetrical above and below ground. This ensures
that both the high and low logic levels will be clamped by the
AD8037. For well controlled signal levels in the output pulse,
the high and low output levels should result from the clamping
action of the AD8037 and not be controlled by either the high
or low logic levels passing through a linear amplifier. For good
rise and fall times at the output pulse, a logic family with high
speed edges should be used.
When the input is negative, the amplifier acts as a regular unitygain inverting amplifier and outputs a positive signal at the same
amplitude as the input with opposite polarity. VL is driven negative by the input, so it performs no clamping action, because the
positive output signal is always higher than the negative level
driving VL.
The high logic levels are clamped at two times the voltage at VH,
while the low logic levels are clamped at two times the voltage
at VL. The output of the AD8037 is amplified by the AD811
operating at a gain of 5. The overall gain of 10 will cause the
high output level to be 10 times the voltage at VH, and the low
output level to be 10 times the voltage at VL.
High Speed, Full-Wave Rectifier
The clamping inputs are additional inputs to the input stage of
the op amp. As such they have an input bandwidth comparable
to the amplifier inputs and lend themselves to some unique
functions when they are driven dynamically.
When the input is positive, the output result is the sum of two
separate effects. First, the inverting amplifier multiplies the input
by –1 because of its unity-gain inverting configuration. This
effectively produces an offset as explained above, but with a
dynamic level that is equal to –1 times the input.
Second, although the positive input is grounded (through 100 Ω),
the output is clamped at two times the voltage applied to VL (a
positive, dynamic voltage in this case). The factor of two is
because the noise gain of the amplifier is two.
The sum of these two actions results in an output that is equal
to unity times the input signal for positive input signals, see Figure 13. For a input/output scope photo with an input signal of
20 MHz and amplitude ± 1 V, see Figure 14.
Figure 12 is a schematic for a full-wave rectifier, sometimes
called an absolute value generator. It works well up to 20 MHz
and can operate at significantly higher frequencies with some
degradation in performance. The distortion performance is significantly better than diode based full-wave rectifiers, especially
at high frequencies.
INPUT
LOWER
CLAMPING
LEVEL WITH
NO NEG INPUT
+5V
0.1F
FULL WAVE
RECTIFIED
OUTPUT
10F
100
VH
AD8037
VOUT = VIN
VL
0.1F
RG
274
RF
274
LOWER
CLAMPING
LEVEL
–1 INPUT
10F
OUTPUT
–5V
VIN
Figure 13.
Figure 12. Full-Wave Rectifier
REV. B
–19–
AD8036/AD8037
The modulation signal is applied to both the input of a unity
gain inverting amplifier and to VL, the lower clamping input.
VH is biased at 0.5 V dc.
To understand the circuit operation, it is helpful to first consider a simpler circuit. If both VL and VH were dc biased at
–0.5 V and the carrier and modulation inputs driven as above,
the output would be a 2 V p-p square wave at the carrier frequency riding on a waveform at the modulating frequency. The
inverting input (modulation signal) is creating a varying offset to
the 2 V p-p square wave at the output. Both the high and low
levels clamp at twice the input levels on the clamps because the
noise gain of the circuit is two.
Figure 14. Full-Wave Rectifier Scope
Thus for either positive or negative input signals, the output is
unity times the absolute value of the input signal. The circuit
can be easily configured to produce the negative absolute value
of the input by applying the input to VH instead of VL.
The circuit can get to within about 40 mV of ground during the
time when the input crosses zero. This voltage is fixed over a
wide frequency range and is a result of the switching between
the conventional op amp input and the clamp input. But because
there are no diodes to rapidly switch from forward to reverse bias,
the performance far exceeds that of diode based full wave rectifiers.
The 40 mV offset mentioned can be removed by adding an offset to the circuit. A 27.4 kΩ input resistor to the inverting input
will have a gain of 0.01, while changing the gain of the circuit
by only 1%. A plus or minus 4 V dc level (depending on the
polarity of the rectifier) into this resistor will compensate for
the offset.
Full wave rectifiers are useful in many applications including
AM signal detection, high frequency ac voltmeters and various
arithmetic operations.
Amplitude Modulator
In addition to being able to be configured as an amplitude
demodulator (AM detector), the AD8037 can also be configured as an amplitude modulator as shown in Figure 15.
When VL is driven by the modulation signal instead of being held
at a dc level, a more complicated situation results. The resulting
waveform is composed of an upper envelope and a lower envelope with the carrier square wave in between. The upper and
lower envelope waveforms are 180° out of phase as in a typical
AM waveform.
The upper envelope is produced by the upper clamp level being
offset by the waveform applied to the inverting input. This offset
is the opposite polarity of the input waveform because of the
inverting configuration.
The lower envelope is produced by the sum of two effects. First,
it is offset by the waveform applied to the inverting input as in
the case of the simplified circuit above. The polarity of this offset is in the same direction as the upper envelope. Second, the
output is driven in the opposite direction of the offset at twice
the offset voltage by the modulation signal being applied to VL.
This results from the noise gain being equal to two, and since
there is no inversion in this connection, it is opposite polarity
from the offset.
The result at the output for the lower envelope is the sum of
these two effects, which produces the lower envelope of an
amplitude modulated waveform. See Figure 16.
VH +5V
0.1F
10F
100
CARRIER IN
VH
AD8037
AM OUT
VL
0.1F
RG
274
RF
274
10F
Figure 16. AM Waveform
–5V
MODULATION IN
Figure 15. Amplitude Modulator
The positive input of the AD8037 is driven with a square wave
of sufficient amplitude to produce clamping action at both the
high and low levels. This is the higher frequency carrier signal.
The depth of modulation can be modified in this circuit by
changing the amplitude of the modulation signal. This changes
the amplitude of the upper and lower envelope waveforms.
The modulation depth can also be changed by changing the dc
bias applied to VH. In this case the amplitudes of the upper and
lower envelope waveforms stay constant, but the spacing between
them changes. This alters the ratio of the envelope amplitude to
the amplitude of the overall waveform.
–20–
REV. B
AD8036/AD8037
Layout Considerations
VH
The specified high speed performance of the AD8036 and
AD8037 requires careful attention to board layout and component
selection. Proper RF design techniques and low pass parasitic
component selection are mandatory.
+VS
1k
RF
–VS
0.1F
The PCB should have a ground plane covering all unused
portions of the component side of the board to provide a low
impedance path. The ground plane should be removed from the
area near the input pins to reduce stray capacitance.
Chip capacitors should be used for supply and input clamp
bypassing (see Figure 17). One end should be connected to
the ground plane and the other within 1/8 inch of each power
and clamp pin. An additional large (0.47 µF–10 µF) tantalum
electrolytic capacitor should be connected in parallel, though
not necessarily so close, to supply current for fast, large signal
changes at the output.
+VS
RG
RO
AD8036/
AD8037
RS
VOUT
IN
RT
–VS
+VS
0.1F
1k
VL
–VS
NONINVERTING CONFIGURATION
The feedback resistor should be located close to the inverting
input pin in order to keep the stray capacitance at this node to a
minimum. Capacitance variations of less than 1 pF at the inverting input will significantly affect high speed performance.
Stripline design techniques should be used for long signal traces
(greater than about 1 inch). These should be designed with a
characteristic impedance of 50 Ω or 75 Ω and be properly terminated at each end.
Evaluation Board
+VS
OPTIONAL
C1
0.01F
C3
0.1F
C5
10F
C2
0.01F
C4
0.1F
C6
10F
–VS
SUPPLY BYPASSING
Figure 17. Noninverting Configurations for Evaluation
Boards
An evaluation board for both the AD8036 and AD8037 is
available that has been carefully laid out and tested to demonstrate that the specified high speed performance of the device
can be realized. For ordering information, please refer to the
Ordering Guide.
The layout of the evaluation board can be used as shown or
serve as a guide for a board layout.
Table I.
REV. B
Component
+1
+2
RF
RG
RO (Nominal)
RS
RT (Nominal)
Small Signal BW (MHz)
140 Ω
274 Ω
274 Ω
49.9 Ω
100 Ω
49.9 Ω
90
49.9 Ω
130 Ω
49.9 Ω
240
AD8036A
Gain
+10
2 kΩ
221 Ω
49.9 Ω
100 Ω
49.9 Ω
10
–21–
+100
+2
AD8037A
Gain
+10
+100
2 kΩ
20.5 Ω
49.9 Ω
100 Ω
49.9 Ω
1.3
274 Ω
274 Ω
49.9 Ω
100 Ω
49.9 Ω
275
2 kΩ
221 Ω
49.9 Ω
100 Ω
49.9 Ω
21
2 kΩ
20.5 Ω
49.9 Ω
100 Ω
49.9 Ω
3
AD8036/AD8037
Figure 18. Evaluation Board Silkscreen (Top)
Figure 20. Board Layout (Solder Side)
Figure 19. Evaluation Board Silkscreen (Bottom)
Figure 21. Board Layout (Component Side)
–22–
REV. B
AD8036/AD8037
OUTLINE DIMENSIONS
Dimensions shown in inches and (mm).
8-Lead Plastic DIP
(N Package)
8
5
0.280 (7.11)
0.240 (6.10)
1
4
0.325 (8.25)
0.300 (7.62)
PIN 1
0.100 (2.54)
BSC
0.060 (1.52)
0.015 (0.38)
0.210
(5.33)
MAX
0.195 (4.95)
0.115 (2.93)
0.130
(3.30)
MIN
0.160 (4.06)
0.115 (2.93)
C01057–0–12/00 (rev. B)
0.430 (10.92)
0.348 (8.84)
0.015 (0.381)
0.008 (0.204)
0.022 (0.558) 0.070 (1.77) SEATING
0.014 (0.356) 0.045 (1.15) PLANE
8-Lead Plastic SOIC
(SO Package)
0.1968 (5.00)
0.1890 (4.80)
0.1574 (4.00)
0.1497 (3.80)
8
5
1
4
0.2440 (6.20)
0.2284 (5.80)
PIN 1
0.0196 (0.50)
45
0.0099 (0.25)
0.0500 (1.27)
BSC
0.0688 (1.75)
0.0532 (1.35)
0.0098 (0.25)
0.0040 (0.10)
SEATING
PLANE
8
0.0500 (1.27)
0.0098 (0.25) 0
0.0160 (0.41)
0.0075 (0.19)
0.0192 (0.49)
0.0138 (0.35)
8-Lead Cerdip
(Q Package)
0.005 (0.13)
MIN
8
0.055 (1.4)
MAX
5
0.310 (7.87)
0.220 (5.59)
PIN 1
1
4
0.200.(5.08)
MAX
0.200 (5.08)
0.125 (3.18)
0.060 (1.52)
0.015 (0.38)
0.150
(3.81)
MIN
SEATING
0.023 (0.58) 0.070 (1.78) PLANE
0.014 (0.36) 0.030 (0.76)
REV. B
–23–
0.320 (8.13)
0.290 (7.37)
15°
0°
0.015 (0.38)
0.008 (0.20)
PRINTED IN U.S.A.
0.100 (2.54) BSC
0.405 (10.29) MAX