a
Quad 3000 V/s, 35 mW
Current Feedback Amplifier
AD8004
GENERAL DESCRIPTION
The AD8004 is a quad, low power, high speed amplifier designed
to operate on single or dual supplies. It utilizes a current feedback architecture and features high slew rate of 3000 V/ms
making the AD8004 ideal for handling large amplitude pulses.
Additionally, the AD8004 provides gain flatness of 0.1 dB to
OUTPUT 1
–IN 2
+VS 4
0.1
–1
5VS
–2
+5VS
–3
0
–4
–0.1
+5VS
–5
5VS
–0.2
–6
–0.3
–7
–0.4
–8
–0.5
1
10
40
FREQUENCY – MHz
100
NORMALIZED FREQUENCY RESPONSE – dB
NORMALIZED FLATNESS – dB
G = +2
VIN = 50mV rms
RL = 100
RF = 1.10k
R PACKAGE
–9
500
Figure 1. Frequency Response and Flatness, G = +2
4
–IN 6
13 –IN
12 +IN
AD8004
(TOP VIEW)
+IN 5
11 –VS
10 +IN
2
3
9 –IN
8 OUTPUT
OUTPUT 7
30 MHz while offering differential gain and phase error of
0.04% and 0.10∞. This makes the AD8004 suitable for video
electronics such as cameras and video switchers.
The AD8004 offers low power of 3.5 mA/amplifier and can run
on a single +4 V to +12 V power supply, while being capable of
delivering up to 50 mA of load current. All this is offered in a
small 14-lead SOIC package. These features make this
amplifier ideal for portable and battery powered applications
where size and power are critical.
The outstanding bandwidth of 250 MHz along with 3000 V/ms
of slew rate make the AD8004 useful in many general-purpose,
high speed applications where dual power supplies of up to ± 6 V
and single supplies from 4 V to 12 V are needed. The AD8004
is available in the industrial temperature range of –40∞C to +85∞C
in the R package.
0.04
0.03
0.02
0.01
0.00
–0.01
–0.02
–0.03
–0.04
0.12
0.10
0.08
0.06
0.04
0.02
0.00
–0.02
–0.04
1
0
14 OUTPUT
1
+IN 3
DIFF GAIN – %
APPLICATIONS
Image Scanners
Active Filters
Video Switchers
Special Effects
CONNECTION DIAGRAM
SOIC (R) Package
DIFF PHASE – Degrees
FEATURES
High Speed
250 MHz –3 dB Bandwidth (G = +1)
3000 V/s Slew Rate
21 ns Settling Time to 0.1%
1.8 ns Rise Time for 2 V Step
Low Power
3.5 mA/Amp Power Supply Current (35 mW/Amp)
Single Supply Operation
Fully Specified for +5 V Supply
Good Video Specifications (RL = 150 , G = +2)
Gain Flatness 0.1 dB to 30 MHz
0.04% Differential Gain Error
0.10 Differential Phase Error
Low Distortion
–78 dBc THD at 5 MHz
–61 dBc THD at 20 MHz
High Output Current of 50 mA
Available in a 14-Lead SOIC
80 IRE
RL = 150
VS = 5V
RF = 1.21k
1ST
2ND 3RD 4TH
5TH
6TH
7TH
8TH
9TH 10TH 11TH
80 IRE
RL = 150
VS = 5V
RF = 1.21k
1ST
2ND 3RD 4TH
5TH
6TH
7TH
8TH
9TH 10TH 11TH
Figure 2. Differential Gain/Differential Phase
REV. D
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. Trademarks and
registered trademarks are the property of their respective companies.
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 © 2003-2015 Analog Devices, Inc. All rights reserved.
AD8004–SPECIFICATIONS (@ T = +25C, V = 5 V, R = 100 , unless otherwise noted.)
A
Parameter
S
L
Test Conditions/Comments
AD8004A
Min Typ Max
AD8004S
Min Typ Max Unit
DYNAMIC PERFORMANCE
Bandwidth for 0.1 dB Flatness
Slew Rate
Settling Time to 0.1%
Rise and Fall Time (10% to 90%)
NOISE/HARMONIC PERFORMANCE
Total Harmonic Distortion
Crosstalk, R Package, Worst Case
Input Voltage Noise
Input Current Noise
Differential Gain Error
Differential Phase Error
Differential Gain Error
Differential Phase Error
G = +2
G = +2, VO = 4 V Step
G = –2, VO = 4 V Step
G = +2, VO = 2 V Step
G = +2, VO = 2 V Step
30
3000
2000
21
1.8
30
3000
2000
21
1.8
MHz
V/µs
V/µs
ns
ns
fC = 5 MHz, VO = 2 V p-p, RL = 1 kΩ
f = 5 MHz, G = +2, RL = 1 kΩ
f = 10 kHz
f = 10 kHz, +In
–In
NTSC, G = +2, RL = 150 Ω, RF = 1.21 kΩ
NTSC, G = +2, RL = 150 Ω, RF = 1.21 kΩ
NTSC, G = +2, RL = 1 kΩ, RF = 1.21 kΩ
NTSC, G = +2, RL = 1 kΩ, RF = 1.21 kΩ
–78
–69
1.5
38
38
0.04
0.10
0.01
0.04
–78
1.5
38
38
0.04
0.10
0.01
0.04
dBc
dB
nV/√Hz
pA/√Hz
pA/√Hz
%
Degree
%
Degree
1.0 3.5
1.5 5
15
± 35 ± 90
± 110
± 40 ± 110
± 120
290
220
1.0 3.5
1.5 6
15
± 35 ± 90
± 120
± 40 ± 110
± 130
290
220
mV
mV
µV/°C
µA
µA
µA
µA
kΩ
kΩ
2
50
1.5
3.2
MΩ
Ω
pF
±V
58
1
12
dB
µA/V
µA/V
3.9
50
180
±V
mA
mA
DC PERFORMANCE
Input Offset Voltage
TMIN to TMAX
Offset Drift
–Input Bias Current
TMIN to TMAX
+Input Bias Current
Open-Loop Transresistance
INPUT CHARACTERISTICS
Input Resistance
Input Capacitance
Input Common-Mode Voltage Range
Common-Mode Rejection Ratio
Offset Voltage
–Input Current
+Input Current
OUTPUT CHARACTERISTICS
Output Voltage Swing
Output Current
Short Circuit Current
TMIN to TMAX
VO = ±2.5 V
TMIN to TMAX
170
+Input
–Input
+Input
2
50
1.5
3.2
VCM = ±2.5 V
VCM = ±2.5 V, TMIN to TMAX
VCM = ±2.5 V, TMIN to TMAX
52
R L = 150 Ω
100
POWER SUPPLY
Operating Range
Total Quiescent Current
Power Supply Rejection Ratio
–Input Current
+Input Current
170
58
1
12
3.9
50
180
± 2.0
TMIN to TMAX
∆VS = ±2 V
TMIN to TMAX
TMIN to TMAX
56
52
14
16
62
0.5
4
100
± 6.0
17
20
± 2.0
56
14
16
62
0.5
4
± 6.0 V
17
mA
23
mA
dB
µA/V
µA/V
Specifications subject to change without notice.
–2–
REV. D
AD8004
SPECIFICATIONS (@ T = +25C, V = +5 V, R = 100 , unless otherwise noted.)
A
Parameter
S
L
Test Conditions/Comments
Min
AD8004A
Typ
Max Min
AD8004S
Typ
Max Unit
DYNAMIC PERFORMANCE
Bandwidth for 0.1 dB Flatness
Slew Rate
Settling Time to 0.1%
Rise and Fall Time (10%
to 90%)
NOISE/HARMONIC
PERFORMANCE
Total Harmonic Distortion
Crosstalk, R Package,
Worst Case
Input Voltage Noise
Input Current Noise
Differential Gain Error
Differential Phase Error
Differential Gain Error
Differential Phase Error
G = +2
G = +2, VO = 2 V Step
G = +2, VO = 2 V Step
30
1100
24
30
1100
24
MHz
V/µs
ns
G = +2, VO = 2 V Step
2.3
2.3
ns
fC = 5 MHz, VO = 2 V p-p, RL = 1 kΩ
–65
–65
dBc
f = 5 MHz, G = +2, RL = 1 kΩ
f = 10 kHz
f = 10 kHz, +In
–In
NTSC, G = +2, RL = 150 Ω, RF = 1.21 kΩ
NTSC, G = +2, RL = 150 Ω, RF = 1.21 kΩ
NTSC, G = +2, RL = 1 kΩ, RF = 1.21 kΩ
NTSC, G = +2, RL = 1 kΩ, RF = 1.21 kΩ
–69
1.5
38
38
0.06
0.25
0.01
0.08
1.5
38
38
0.06
0.25
0.01
0.08
dB
nV/√Hz
pA/√Hz
pA/√Hz
%
Degree
%
Degree
DC PERFORMANCE
Input Offset Voltage
1.0
1
15
±20
TMIN to TMAX
Offset Drift
–Input Bias Current
TMIN to TMAX
±35
+Input Bias Current
Open Loop Transresistance
INPUT CHARACTERISTICS
Input Resistance
TMIN to TMAX
VO = +1.5 V to +3.5 V
TMIN to TMAX
140
+Input
–Input
+Input
Input Capacitance
Input Common-Mode
Voltage Range
Common-Mode Rejection Ratio
Offset Voltage
VCM = +1 V to +3 V
–Input Current
VCM = +1 V to +3 V, TMIN to TMAX
+Input Current
VCM = +1 V to +3 V, TMIN to TMAX
52
OUTPUT CHARACTERISTICS
Output Voltage Swing
R L = 150 Ω
Output Current
Short Circuit Current
±80
±100
±100
±115
230
170
±35
140
TMIN to TMAX
∆VS = +1 V, VCM = +2.5 V
TMIN to TMAX
TMIN to TMAX
56
–3–
230
170
2.5
4
mV
mV
µV/°C
±80 µA
±110 µA
±100 µA
±125 µA
kΩ
kΩ
2
50
1.5
2
50
1.5
MΩ
Ω
pF
3.2
3.2
V
57
2
15
dB
µA/V
µA/V
0.9 to 4.1
50
95
V
mA
mA
57
2
15
0, +4
Specifications subject to change without notice.
REV. D
1.0
1
15
±20
52
0.9 to 4.1
50
95
POWER SUPPLY
Operating Range
Total Quiescent Current
Power Supply Rejection Ratio
–Input Current
+Input Current
2.5
3
13
14.5
62
1
6
+12
14
15.5
0, +4
56
13
14.5
62
1
6
+12
14
17.5
V
mA
mA
dB
µA/V
µA/V
AD8004
ABSOLUTE MAXIMUM RATINGS1, 2
MAXIMUM POWER DISSIPATION
Supply Voltage . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12.6 V
Internal Power Dissipation . . . . . . . . . . . . . . . . . . . . . Note 2
Input Voltage (Common Mode) . . . . . . . . . . . . . . . . . . . . ± VS
Differential Input Voltage . . . . . . . . . . . . . . . . . . . . . . . ± 2.5 V
Output Short Circuit Duration
. . . . . . . . . . . . . . . . . . . . . . Observe Power Derating Curves
Storage Temperature Range (R) . . . . –65°C to +125°C
Operating Temperature Range
A Grade . . . . . . . . . . . . . . . . . . . . . . . . . . . . –40°C to +85°C
S Grade . . . . . . . . . . . . . . . . . . . . . . . . . . . –55°C to +125°C
Lead Temperature Range (Soldering 10 sec) . . . . . . . . +300°C
The maximum power that can be safely dissipated by the
AD8004 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 AD8004 is internally short circuit protected, this may
not be sufficient to guarantee that the maximum junction temperature is not exceeded under all conditions. To ensure proper
operation, it is necessary to observe the maximum power ratings.
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:
14-Lead SOIC Package: θJA = 140°C/W, θJC = 30°C/W
ORDERING GUIDE
Model 1
Temperature
Range
Package
Description
Package
Option
AD8004ARZ-14
– 40°C to +85°C
14-Lead SOIC
R-14
R-14
AD8004ARZ-14-REEL7 –40°C to +85°C
AD8004AR-EBZ
1
7" Tape and Reel
Evaluation Board
Z = RoHS Compliant Part.
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 AD8004 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.
604
604
50
SCOPE
INPUT
249
499
50
SCOPE
INPUT
VIN
50
VIN
50
50
61.9
+VS
+VS
0.1F
10F
0.1F
10F
0.1F
10F
0.1F
10F
–VS
–VS
Figure 4. Test Circuit; Gain = –2
Figure 3. Test Circuit; Gain = –2
–4–
REV. D
Typical Performance Characteristics– AD8004
TPC 1.1 100 mV Step Response; G = +2, VS = ±2.5 V or ±5 V
TPC 4.1 100 mV Step Response; G = –2, VS = ±2.5 V or ±5 V
TPC 2.1 Step Response; G = +2, VS = ±5 V
TPC 5.1 Step Response; G = –2, VS = ±5 V
1
G = +1,
RF = 698
1
NORMALIZED FREQUENCY RESPONSE – dB
NORMALIZED FREQUENCY RESPONSE – dB
2
0
RL = 100
VIN = 50mV (G = +1, +2)
VIN = 5mV (G = +10)
–1
–2
G = +2,
RF = 604
–3
–4
–5
G = +10,
RF = 499
–6
–7
–8
VS = 5V
RF = 499
VIN = 50mV rms
RL = 100
N PACKAGE
–1
–2
–3
G = –2
G = –10
–4
–5
–6
–7
–8
–9
1
10
40
FREQUENCY – MHz
100
1
500
TPC 3. Frequency Response; G = +1, +2, +10; VS = ± 5 V
10
40
FREQUENCY – MHz
100
500
TPC 6.2 Frequency Response; G = –1, –2, –10
1
VS = ±2.5 V operation is identical to VS = +5 V single-supply operation.
2
The N-14 package option is no longer available; the R-14 package performance may vary.
REV. D
G = –1
0
–5–
AD8004
9
3
6
0
1V rms
–3
3
OUTPUT LEVEL – dBV
OUTPUT LEVEL – dBV
1V rms
0
–3
–6
–9
–12
G = +2
VS = 5V
RF = 604
–15
–6
–9
–12
–15
–18
–24
–18
–21
1
10
40
FREQUENCY – MHz
–27
500
100
TPC 7. Large Signal Frequency Response; VS = ± 5.0 V,
G = +2, RF = 604 Ω
1
10
40
FREQUENCY – MHz
500
–40
G = +2
VO = 2V p-p
RF = 698
–50
2ND
RL = 150
–60
–70
–80
2ND
RL = 1k
–90
10
1
–70
–80
2ND
RL = 1k
–100
1
20
10
TPC 11. Distortion vs. Frequency; VS = +5 V
–10
1
–2
–3
0
–4
–0.1
–5
+5VS
5VS
–0.2
–6
–0.3
–7
–0.4
–8
–0.5
–9
500
1
10
40
FREQUENCY – MHz
100
–15
604
50
VIN
–25
VOUT
154
–20
CMRR – dB
0.1
–1
5VS
604
NORMALIZED FREQUENCY RESPONSE – dB
0
5VS
20
FREQUENCY – MHz
TPC 8. Distortion vs. Frequency; VS = ± 5 V
+5VS
3RD
RL = 150
3RD
RL = 1k
–60
FREQUENCY – MHz
G = +2
VIN = 50mV rms
RL = 100
RF = 1.10k
R PACKAGE
2ND
RL = 150
–90
3RD
RL = 1k
–100
G = +2
VO = 2V p-p
RF = 698
3RD
RL = 150
DISTORTION – dBc
–50
NORMALIZED FLATNESS – dB
100
TPC 10. Large Signal Frequency Response; VS = +5.0 V,
G = +2, RF = 604 Ω
–40
DISTORTION – dBc
G = +2
VS = +5V
RF = 604
–21
57.6
154
+5VS
–30
–35
–40
–45
–50
+5VS
–55
5VS
–60
0.03
0.1
1
10
FREQUENCY – MHz
100
500
TPC 12. CMRR vs. Frequency; VS = ± 5 V or +5 V,
VIN = 200 mV rms, Other Sides Are Equal, RTO
TPC 9. Frequency Response and Flatness, G = +2
–6–
REV. D
AD8004
100
1000
200
10
100
70
+ OR – INPUT
CURRENT NOISE
50
40
30
20
VOLTAGE NOISE
1
10
100
1k
10k
FREQUENCY – Hz
100k
–20
G = +2
5VS OR 2.5VS
RF = 1k
100mV rms ON TOP
OF dc BIAS
+PSRR
–30
PSRR – dB
300
–10
INPUT CURRENT NOISE – pA/ Hz
INPUT VOLTAGE NOISE – nV/ Hz
500
0
–40
–PSRR
–50
–60
–70
10
1M
–80
10k
100k
TPC 13. Noise vs. Frequency, VS = +5 V or ± 5 VS
1M
10M
FREQUENCY – Hz
100M
500M
TPC 16. PSRR vs. Frequency
–20
–30
G = +2
RF = 698
POWER = 0dBm
(224mV rms)
10
+5VS
1
–40
RBT = 50
5VS OR +5VS
CROSSTALK – dB
IMPEDANCE –
100
RBT = 0
–50
–60
G = +2
RF = 1.10k
5VS
VIN = 200mV rms
INPUT TO SIDE 1
RL1 = 1k
R PACKAGE
OUTPUT =
SIDE 2
OUTPUT =
SIDE 4
–70
–80
OUTPUT =
SIDE 3
–90
5VS
0.1
–100
–110
0.01
0.03
0.1
1
10
FREQUENCY – MHz
100
–120
0.03
500
TPC 14. Output Impedance vs. Frequency
0.1
1
10
FREQUENCY – MHz
100
500
TPC 17. Crosstalk (Output to Output) vs. Frequency
110
0
GAIN
60
100
50
90
40
80
20
10
–240
VIN = –40dBm
VS = 5V
–50
PHASE
60
–100
50
0
40
30
–150
20
0.1
1
10
FREQUENCY – MHz
100
10
100k
500
TPC 15. Open-Loop Voltage Gain and Phase
REV. D
70
–10
–360
0.03
0
1M
10M
FREQUENCY – Hz
100M
–200
1G
TPC 18. Open-Loop Transimpedance Gain
–7–
PHASE – Degrees
30
PHASE
–180
GAIN – dB
90
GAIN – dB
PHASE – Degrees
GAIN
AD8004
9
G = +2
RF = 1.21k
8
5VS
7
SWING – V p-p
6
5
4
3
+5VS
2
1
0
10
100
1000
LOAD RESISTANCE –
10000
TPC 22. Output Voltage Swing vs. Load
TPC 19. Short-Term Settling Time
10
9
G = +2
RF = 1.21k
f = 100kHz
PEAK-TO-PEAK OUTPUT
AT CLIPPING POINT – V
8
RL = 1k
7
6
RL = 100
5
4
3
2
1
0
5
6
7
8
9
10
TOTAL SUPPLY VOLTAGE – V
11
12
DIFF GAIN – %
0.03
0.04
0.03
0.02
0.01
0.00
–0.01
–0.02
–0.03
–0.04
80 IRE
RL = 150
VS = 5V
RF = 1.21k
80 IRE
RL = 1k
VS = 5V
RF = 1.21k
0.02
0.01
0.00
–0.01
–0.02
–0.03
1ST
2ND 3RD 4TH 5TH
6TH
7TH
0.12
0.10
0.08
0.06
0.04
0.02
0.00
–0.02
–0.04
8TH
1ST
9TH 10TH 11TH
DIFF PHASE – Degrees
DIFF GAIN – %
4
TPC 23. Output Swing vs. Supply
TPC 20. Long-Term Settling Time
DIFF PHASE – Degrees
3
80 IRE
RL = 150
VS = 5V
RF = 1.21k
1ST
2ND 3RD 4TH 5TH
6TH
7TH
8TH
5TH
6TH
7TH
8TH
9TH 10TH 11TH
8TH
9TH 10TH 11TH
80 IRE
RL = 1k
VS = 5V
RF = 1.21k
1ST
9TH 10TH 11TH
2ND 3RD 4TH
0.04
0.03
0.02
0.01
0.00
–0.01
–0.02
–0.03
–0.04
2ND 3RD 4TH
5TH
6TH
7TH
TPC 24. Differential Gain/Phase, RL = 1 kΩ
TPC 21. Differential Gain/Differential Phase
–8–
REV. D
AD8004
The more exact relationships that take into account open-loop
gain errors are:
THEORY OF OPERATION
The AD8004 is a member of a new family of high speed currentfeedback (CF) amplifiers offering new levels of bandwidth,
distortion, and signal-swing capability vs. power. Its wide dynamic
range capabilities are due to both a complementary high speed
bipolar process and a new design architecture. The AD8004 is
basically a two stage (Figure 30) rather than the conventional
one stage design. Both stages feature the current-on-demand
property associated with current feedback amplifiers. This
gives an unprecedented ratio of quiescent current to dynamic
performance. The important properties of slew rate and full
power bandwidth benefit from this performance. In addition
the second gain stage buffers the effects of load impedance,
significantly reducing distortion.
AV =
DC AND AC CHARACTERISTICS
As with traditional op amp circuits the dc closed-loop gain is
defined as:
RF
RN
R
AV = G = − F
RN
for inverting (G is negative)
G
RF
G
1+
+
AO (s) T O (s)
for noninverting (G is positive)
In these equations the open-loop voltage gain (AO(s)) is common
to both voltage and current-feedback amplifiers and is the ratio
of output voltage to differential input voltage. The open-loop
transimpedance gain (TO(s)) is the ratio of output voltage to
inverting input current and is applicable to current-feedback
amplifiers. The open-loop voltage gain and open-loop transimpedance gain (TO(s)) of the AD8004 are plotted vs. frequency
in TPCs 15 and 18. These plots and the basic relationships can
be used to predict the first order performance of the AD8004 over
frequency. At low closed-loop gains the term (RF/TO(s)) dominates
the frequency response characteristics. This gives the result that
bandwidth is constant with gain, a familiar property of current
feedback amplifiers.
A full discussion of this new amplifier architecture is available on
the data sheet for the AD8011. This discussion only covers the
basic principles of operation.
AV = G = 1 +
G
RF
1− G
1+
+
AO (s) T O (s)
AV =
noninverting operation
An RF of 1 k⍀ has been chosen as the nominal value to give
optimum frequency response with acceptable peaking at gains of
+2/–1. As can be seen from the above relationships, at higher
closed-loop gains reducing RF has the effect of increasing closedloop bandwidth. Table I gives optimum values for RF and RG
for a variety of gains.
inverting operation
A1
CD
IPP
IPN
IQ1
A2
C P1
Q3
CP2
Q1
ICQ + IO
VN
VP
V O´
ZI
A3
Q2
RF
IE
RG
Q4
IQ1
A2
INP
IPN
A1
C P1
CD
AD8004
Figure 5. Simplified Block Diagram
REV. D
VO
RL
Z2
–9–
CL
AD8004
DRIVING CAPACITIVE LOADS
The AD8004 was designed primarily to drive nonreactive loads.
If driving loads with a capacitive component is desired, best
settling response is obtained by the addition of a small series
resistance as shown in Figure 6. 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.
1k⍀
RSERIES
AD8004
1k⍀
RL
1k⍀
CL
Figure 6. Driving Capacitive Load
In noninverting gains, the effect of extra capacitance on
summing junctions is far more pronounced than with inverting
gains. Figure 9 shows an example of this. Note that only 1 pF of
added junction capacitance causes about a 70% bandwidth
extension and additional peaking on a gain = +2. For an inverting
gain = –2, 5 pF of additional summing junction capacitance
caused a small 10% bandwidth extension.
Extra output capacitive loading also causes bandwidth extensions and peaking. The effect is more pronounced with less
resistive loading from the next stage. Figure 10 shows the effect
of direct output capacitive loads for gains of +2 and –2. For both
gains CLOAD was set to 10 pF or 0 pF (no extra capacitive loading).
For each of the four traces in Figure 10 the resistive loads were
100 ⍀. Figure 11 also shows capacitive loading effects with a
lighter output resistive load. Note that even though bandwidth
is extended 2¥, the flatness dramatically suffers.
2
40
RF = 698⍀
1
RF = 1.1k⍀
0
RF = 909⍀
RSERIES – ⍀
NORMALIZED GAIN – dB, G = +2
30
20
0
5
10
15
20
–2
RF = 604⍀
G = +2
–3
0
–4
–1
VIN = 50mV rms
VS = ⴞ5V
RL = 100⍀
R PACKAGE
–2
–3
–5
–5
–6
RF = 845⍀
–4
25
RF = 1.10k⍀
1
10
40
FREQUENCY – MHz
CL – pF
–7
–8
500
100
Figure 8. RFEEDBACK vs. Frequency Response, G = +1/+2
Figure 7. Recommended RSERIES vs. Capacitive Load for
£ 30 ns Settling to 0.1%
2
OPTIMIZING FLATNESS
G = +2
The fine scale gain flatness and –3 dB bandwidth is affected by
RFEEDBACK selection as is normal of current feedback amplifiers.
With the exception of gain = +1, the AD8004 can be adjusted
for either maximal flatness with modest closed-loop bandwidth
or for mildly peaked-up frequency response with much more
bandwidth. Figure 8 shows the effect of three evenly spaced R F
changes upon gain = +1 and gain = +2. Table I shows the
recommended component values for achieving maximally flat
frequency response as well as a faster slightly peaked-up frequency response.
CJ = 1pF
CJ = 0
2
0
–2
NORMALIZED GAIN – dB, G = –2
G = –2
Printed circuit board parasitics and device lead frame parasitics
also control fine scale gain flatness. In the printed circuit board
environment, parasitics such as extra capacitance caused by two
parallel and vertical flat conductors on opposite PC board
sides in the region of the summing junction will cause some
bandwidth extension and/or increased peaking.
0
–4
–6
–2
VIN = 50mV rms
RL = 100⍀
ⴞ5VS
–4
–6
–8
CJ = 5.1pF
–10
–12
–8
NORMALIZED GAIN – dB, G = +2
10
1
–1
GAIN – dB, G = +1
G = +1
CJ = 0
–14
–10
–12
–14
1
10
40
FREQUENCY – MHz
100
500
Figure 9. Frequency Response vs. Added Summing
Junction Capacitance
–10–
REV. D
AD8004
2
CL = 10pF
0
CL = 0
–2
NORMALIZED GAIN – dB, G = –2
2
G = –2, RF = 698
0
–4
–6
–2
CL = 10pF
–4
VIN = 50mV
5VS
RL = 100
–6
–8
–8
–10
CL = 0
–12
through R2. This current flows toward the summing junction
and requires that the output be 2 V higher than the summing
junction or at 3.6 V.
NORMALIZED GAIN – dB, G = +2
G = +2, RF = 1.10k
When the input is at 1 V, there is 1.2 mA flowing into the summing junction through R3 and 1.2 mA flowing out through R1.
These currents balance and leave no current to flow through
R2. Thus the output is at the same potential as the inverting
input or 1.6 V.
The input of the AD876 has a series MOSFET switch that turns
on and off at the sampling rate. This MOSFET is connected to
a hold capacitor internal to the device. The on impedance of the
MOSFET is about 50 Ω, while the hold capacitor is about 5 pF.
–14
–10
–12
–14
1
10
40
FREQUENCY – MHz
100
In a worst case condition, the input voltage to the AD876 will
change by a full-scale value (2 V) in one sampling cycle. When
the input MOSFET turns on, the output of the op amp will be
connected to the charged hold capacitor through the series
resistance of the MOSFET. Without any other series resistance,
the instantaneous current that flows would be 40 mA. This
would cause settling problems for the op amp.
500
Figure 10. Frequency Response vs. Capacitive Loading,
RL = 100 Ω Output
2
CL = 10pF
NORMALIZED GAIN – dB, G = 2
0
G = +2
RL = 1k
5VS
VIN = 50mV rms
RF = 1.2k
–2
–4
The series 100 Ω resistor limits the current that flows instantaneously after the MOSFET turns on to about 13 mA. This
resistor cannot be made too large or the high frequency performance will be affected.
CL = 0
The sampling MOSFET of the AD876 is closed for only half of
each cycle or for 25 ns. Approximately seven time constants are
required for settling to 10 bits. The series 100 Ω resistor along
with the 50 Ω on resistance and the hold capacitor, create a
750 ps time constant. These values leave a comfortable margin
for settling. Obtaining the same results with the op amp A/D
combination as compared to driving with a signal generator
indicates that the op amp is settling fast enough.
–6
–8
–10
–12
–14
1
10
40
FREQUENCY – MHz
100
500
Overall the AD8004 provides adequate buffering for the AD876
A/D converter without introducing distortion greater than that
of the A/D converter by itself.
Figure 11. Flatness with 10 pF Capacitive Load
DRIVING A SINGLE-SUPPLY A/D CONVERTER
New CMOS A/D converters are placing greater demands on the
amplifiers that drive them. Higher resolutions, faster conversion
rates, and input switching irregularities require superior settling
characteristics. In addition, these devices run off a single +5 V
supply and consume little power, so good single-supply operation
with low power consumption is very important. The AD8004 is
well positioned for driving this new class of A/D converters.
+5V
R3
1.65k
0.1F
10F
0.1F
1V
0V
Figure 12 shows a circuit that uses an AD8004 to drive an
AD876, a single supply, 10-bit, 20 MSPS A/D converter that
requires only 140 mW. Using the AD8004 for level shifting and
driving, the A/D exhibits no degradation in performance compared to when it is driven from a signal generator.
+3.6V
R1
499k
VIN
REFT
100
1/4
AD8004
50
AD876
3.6V
0.1F
1.6V
1.6V
REFB
+1.6V
Figure 12. AD8004 Driving the AD876
The analog input of the AD876 spans 2 V centered at about
2.6 V. The resistor network and bias voltages provide the level
shifting and gain required to convert the 0 V to 1 V input signal
to a 3.6 V to 1.6 V range that the AD876 wants to see.
LAYOUT CONSIDERATIONS
Biasing the noninverting input of the AD8004 at 1.6 V dc forces
the inverting input to be at 1.6 V dc for linear operation of the
amplifier. When the input is at 0 V, there is 3.2 mA flowing out
of the summing junction via R1 (1.6 V/499 Ω). R3 has a current
of 1.2 mA flowing into the summing junction (3.6 V – 1.6 V)/
1.65 kΩ. The difference of these two currents (2 mA) must flow
REV. D
R2
1k
3.6V
The specified high speed performance of the AD8004 requires
careful attention to board layout and component selection.
Table I shows the recommended component values for the
AD8004 and Figures 14–16 show the layout for the AD8004
evaluation board (14-lead SOIC). Proper RF design techniques
and low parasitic component selection are mandatory.
–11–
AD8004
The PCB should have a ground plane covering all unused portions
of the component side of the board to provide a low impedance
ground path. The ground plane should be removed from the
area near the input pins to reduce stray capacitance.
RF
RG
RBT, 50
VIN
VOUT
RT
1/4
Chip capacitors should be used for supply bypassing (see
Figure 13). One end should be connected to the ground plane and
the other within 1/8" of each power pin. An additional (4.7 µF to
10 µF) tantalum electrolytic capacitor should be connected in
parallel.
C1
0.1F
C3
10F
C2
0.1F
C4
10F
+VS
–VS
INVERTING CONFIGURATION
RF
RG
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 greater than 1 pF at the inverting input
will significantly affect high speed performance when operating
at low noninverting gains. An example of extra inverting input
capacitance can be seen on the plot of Figure 10.
RBT, 50
VOUT
1/4
VIN
RT
C1
0.1F
C3
10F
C2
0.1F
C4
10F
+VS
–VS
Stripline design techniques should be used for long signal traces
(greater than about 1"). These should be designed with the
proper system characteristic impedance and be properly terminated at each end.
NONINVERTING CONFIGURATION
Figure 13. Inverting and Noninverting Configurations
Table I. Recommended Component Values1 and Typical Bandwidths
Gain
AD8004 (SOIC)
PACKAGE TYPE
RF (Ω)
RG (Ω)
RT2 (Ω)
Small Signal BW
@ ± 5 VS (MHz)
–10
–2
Alternate
–2
–1
Alternate
–1
499
49.9
None
698
348
57.6
499
249
61.9
750
750
53.6
499
499
54.9
155
130
190
125
Peaking @ ± 5 VS
< 0.7 dB
< 0.1 dB
0.5 dB
None
0.1 dB Flatness
@ ± 5 VS (MHz)
Small Signal BW
@ +5 VS (MHz)
35
135
115
+1
Alternate
+1
+2
Alternate
+2
+10
1.10 k
698
50
1.10 k
1.10 k
50
604
604
50
499
54.9
50
50
195
150
225
110
175
135
0.4 dB
1.3 dB
1.8 dB
< 0.1 dB
0.5 dB
< 0.2 dB
155
120
25
175
110
30
165
130
195
95
NOTES
1
Resistor values listed are standard 1% tolerance.
2
RT chosen for 50 Ω characteristic input impedance.
–12–
REV. D
AD8004
Figure 14.1 Evaluation Board Silkscreen (Top)
1
The DIP package option is no longer available.
REV. D
–13–
AD8004
Figure 15 Evaluation Board Layout (Top Side)
Figure 16.1 Evaluation Board Layout (Bottom Side, Looking Through the Board)
1
The DIP package option is no longer available.
–14–
REV. D
AD8004
OUTLINE DIMENSIONS
14-Lead Standard Small Outline Package [SOIC]
(R-14)
Dimensions shown in millimeters and (inches)
8.75 (0.3445)
8.55 (0.3366)
4.00 (0.1575)
3.80 (0.1496)
14
8
1
7
0.25 (0.0098)
0.10 (0.0039)
COPLANARITY
0.10
1.27 (0.0500)
BSC
0.51 (0.0201)
0.33 (0.0130)
6.20 (0.2441)
5.80 (0.2283)
1.75 (0.0689)
1.35 (0.0531)
SEATING
PLANE
0.50 (0.0197)
45
0.25 (0.0098)
8
0.25 (0.0098) 0 1.27 (0.0500)
0.40 (0.0157)
0.19 (0.0075)
COMPLIANT TO JEDEC STANDARDS MS-012AB
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. D
–15–
AD8004
Revision History
Location
Page
12/15—Data Sheet changed from REV. C to REV. D.
Changes to ORDERING GUIDE . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4
3/03—Data Sheet changed from REV. B to REV. C.
Updated format . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .Universal
Added CERDIP (Q) Package . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1
Added text to GENERAL DESCRIPTION . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1
D01045–0–12/15(D)
Deleted 14-Lead PDIP and 14-Lead CERDIP Package . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .Universal
Changes to SPECIFICATIONS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2
Changes to ABSOLUTE MAXIMUM RATINGS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4
Changes to ORDERING GUIDE . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4
Edited MAXIMUM POWER DISSIPATION section . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4
Deleted Figure 3 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4
Edited Y axis of TPC 13 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7
Edited OPTIMIZING FLATNESS section . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10
Edits to Figure 13 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12
Changes to Table I . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12
PRINTED IN U.S.A.
Updated OUTLINE DIMENSIONS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15
–16–
REV. D
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