Dual-Channel Ultralow Noise Amplifier with
Selectable Gain and Input Impedance
AD8432
Low noise
Input voltage noise: 0.85 nV/√Hz
Current noise: 2.0 pA/√Hz
High speed
200 MHz bandwidth (G = 12.04 dB)
295 V/µs slew rate
Selectable gain
G = 12.04 dB (×4)
G = 18.06 dB (×8)
G = 21.58 dB (×12)
G = 24.08 dB (×16)
Active input impedance matching
Integrated input clamp diodes
Single-ended input, differential output
Supply range: 4.5 V to 5.5 V
Low power: 60 mW/channel
FUNCTIONAL BLOCK DIAGRAM
ENB
VPS1
VPS2
COMM
BIAS
AD8432
INH1
IND1
OPH1
LNA1
OPL1
GMH1
GOH1
GOL1
GML1
INL1
INH2
OPH2
IND2
LNA2
OPL2
GMH2
GOH2
GOL2
GML2
INL2
08341-001
FEATURES
Figure 1.
APPLICATIONS
CW Doppler ultrasound front ends
Low noise preamplification
Predriver for I/Q demodulators and phase shifters
Wideband analog-to-digital drivers
GENERAL DESCRIPTION
The AD8432 is a dual-channel, low power, ultralow noise
amplifier with selectable gain and active impedance matching.
Each channel has a single-ended input, differential output, and
integrated input clamps. By pin strapping the gain setting pins, four
accurate gains of G = 12.04 dB, 18.06 dB, 21.58 dB, and 24.08 dB
(×4, ×8, ×12, and ×16, respectively) are possible. A bandwidth of
200 MHz at G = 12.04 dB makes this amplifier well suited for many
high speed applications.
The exceptional noise performance of the AD8432 is made
possible by the active impedance matching. Using a feedback
network, the input impedance of the amplifiers can be adjusted
to match the signal source impedance without compromising
the noise performance. Impedance matching and low noise in
the AD8432 allow designers to create wider dynamic range
systems that are able to detect even very low level signals.
The AD8432 achieves 0.85 nV/√Hz input-referred voltage noise for
a gain of 12.04 dB. The AD8432’s ultralow noise, low distortion,
gain accuracy, and channel-to-channel matching are ideal for
high performance ultrasound systems and for processing I/Q
demodulator signals.
The AD8432 operates on a single supply of 5 V at 24 mA. It is
available in a 4 mm × 4 mm, 24-lead LFSCP. The LFCSP features
an exposed paddle that provides a low thermal resistance path to
the PCB, which enables more efficient heat transfer and increases
reliability. The operating temperature range is −40°C to +85°C.
Rev. A
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. Specifications subject to change without notice. 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 owners.
One Technology Way, P.O. Box 9106, Norwood, MA 02062-9106, U.S.A.
www.analog.com
Tel: 781.329.4700
Fax: 781.461.3113 ©2009-2010 Analog Devices, Inc. All rights reserved.
AD8432
TABLE OF CONTENTS
Features .............................................................................................. 1
Gain Setting Technique ............................................................. 18
Applications ....................................................................................... 1
Active Input Resistance Matching............................................ 19
Functional Block Diagram .............................................................. 1
Applications Information .............................................................. 21
General Description ......................................................................... 1
Typical Setup ............................................................................... 21
Revision History ............................................................................... 2
I/Q Demodulation Front End ................................................... 23
Specifications..................................................................................... 3
Differential-to-Single-Ended Conversion............................... 24
Absolute Maximum Ratings ............................................................ 5
Evaluation Board ............................................................................ 25
Thermal Resistance ...................................................................... 5
Gain Setting ................................................................................. 25
Maximum Power Dissipation ..................................................... 5
Schematic..................................................................................... 26
ESD Caution .................................................................................. 5
Power Supply............................................................................... 27
Pin Configuration and Function Descriptions ............................. 6
Input Termination ...................................................................... 27
Typical Performance Characteristics ............................................. 7
Output .......................................................................................... 27
Test Circuits ..................................................................................... 16
Outline Dimensions ....................................................................... 28
Theory of Operation ...................................................................... 18
Ordering Guide .......................................................................... 28
Low Noise Amplifier (LNA) ..................................................... 18
REVISION HISTORY
2/10—Rev. 0 to Rev. A
Changes to General Description .................................................... 1
Changes to Figure 5, Figure 6, Figure 7, Figure 8 ......................... 7
Added Figure 27, Figure 29, and Figure 31, Renumbered
Sequentially ..................................................................................... 11
Added Figure 33 and Figure 35..................................................... 12
Changes to Figure 58 ...................................................................... 16
10/09—Revision 0: Initial Version
Rev. A | Page 2 of 28
AD8432
SPECIFICATIONS
VS = 5 V, TA = 25°C, RS = RIN = 50 Ω, RFB =150 Ω, CSH = 47 pF, RSH = 15 Ω, RL = 500 Ω (per SE output), CL = 5 pF (per SE output),
G = 12.04 dB (single-ended input to differential output), f = 1 MHz, unless otherwise specified.
Table 1.
Parameter
DYNAMIC PERFORMANCE
Gain Range
Gain Error
−3 dB Small Signal Bandwidth
−3 dB Large Signal Bandwidth
Slew Rate (Rising Edge)
Slew Rate (Falling Edge)
Overdrive Recovery Time
DISTORTION/NOISE PERFORMANCE
Input Voltage Noise
Input Current Noise
Noise Figure
Unterminated
Active Termination
Output Referred Noise
Harmonic Distortion
1 MHz (VOUT = 1 V p-p)
1 MHz (VOUT = 2 V p-p)
10 MHz (VOUT = 1 V p-p)
10 MHz (VOUT = 2 V p-p)
Conditions
Min
Input to differential output (selectable gain)
Input to single output (selectable gain)
12.04
6.02
RIN unterminated, RFB = ∞, CSH = 0 pF, RSH = 0 Ω
G = 12.04 dB
G = 18.06 dB
G = 21.58 dB
G = 24.08 dB
VOUT = 2 V p-p
VOUT = 2 V p-p, f = 10 MHz
VOUT = 2 V p-p, f = 10 MHz
Typ
Max
Unit
0.1
24.08
18.06
1
dB
dB
dB
200
90
50
32
42
295
170
10
MHz
MHz
MHz
MHz
MHz
V/µs
V/µs
ns
RFB = ∞
RFB = ∞
0.85
2.0
nV/√Hz
pA/√Hz
RS = 50 Ω, RFB = ∞
RS = RIN = 50 Ω, RFB = 150 Ω
RS = 50 Ω, RFB = 226 Ω, RIN = 75 Ω
RS = 50 Ω, RFB = 301 Ω, RIN = 100 Ω
RS = 50 Ω, RFB = 619 Ω, RIN = 200 Ω
RS = 50 Ω, RFB = 3.57 kΩ, RIN = 1 kΩ
G = 12.04 dB, RFB = ∞
G = 18.06 dB, RFB = ∞
G = 21.58 dB, RFB = ∞
G = 24.08 dB, RFB = ∞
2.8
4.8
4.2
3.2
2.1
2.3
3.4
6.8
10.2
13.6
dB
dB
dB
dB
dB
dB
nV/√Hz
nV/√Hz
nV/√Hz
nV/√Hz
HD2
HD2, RS = 50 Ω, RIN unterminated
HD3
HD3, RS = 50 Ω, RIN unterminated
HD2
HD2, RS = 50 Ω, RIN unterminated
HD3
HD3, RS = 50 Ω, RIN unterminated
HD2
HD2, RS = 50 Ω, RIN unterminated
HD3
HD3, RS = 50 Ω, RIN unterminated
HD2
HD2, RS = 50 Ω, RIN unterminated
HD3
HD3, RS = 50 Ω, RIN unterminated
−67
−74
−103
−106
−65
−72
−103
−92
−66
−62
−78
−73
−60
−56
−72
−65
dBc
dBc
dBc
dBc
dBc
dBc
dBc
dBc
dBc
dBc
dBc
dBc
dBc
dBc
dBc
dBc
Rev. A | Page 3 of 28
AD8432
Parameter
Two-Tone IMD3 Distortion
10 MHz
1 MHz
Input 1dB Compression Point
Output Third-Order Intercept
1 MHz
10 MHz
1 MHz
10 MHz
Crosstalk
DC PERFORMANCE
Input Offset Voltage
Input Offset Voltage Drift
INPUT CHARACTERISTICS
Input Voltage Range
Input Resistance
Input Capacitance
Input Common-Mode Voltage
OUTPUT CHARACTERISTCS
Output Common-Mode Voltage
Output Offset Voltage
Output Voltage Swing
Output Resistance
Output Resistance in Shutdown Mode
Output Short-Circuit Current
Enable Response Time
POWER SUPPLY
Supply Voltage
Quiescent Current
Over Temperature
Supply Current in Shutdown Mode
Power Dissipation
PSRR
Conditions
RS = 50 Ω, RIN unterminated
VOUT = 1 V p-p, f1 = 9.5 MHz, f2 = 10.5 MHz
VOUT = 2 V p-p, f1 = 9.5 MHz, f2 = 10.5 MHz
VOUT = 1 V p-p, f1 = 0.9 MHz, f2 = 1.1 MHz
VOUT = 2 V p-p, f1 = 0.9 MHz, f2 = 1.1 MHz
f = 1 MHz
f = 10 MHz
Min
VOUT = 1 V p-p of composite tones
VOUT = 2 V p-p of composite tones
VOUT = 1 V p-p of composite tones
VOUT = 2 V p-p of composite tones
VOUT = 1 V p-p of composite tones, reference to 50 Ω
VOUT = 2 V p-p of composite tones, reference to 50 Ω
VOUT = 1 V p-p of composite tones, reference to 50 Ω
VOUT = 2 V p-p of composite tones, reference to 50 Ω
VOUT = 1 V p-p, f = 1 MHz
−6.25
AC-coupled
RFB = 150 Ω
RFB = 226 Ω
RFB = 301 Ω
RFB = 619 Ω
RFB = 3.57 kΩ
RFB = ∞, f = 100 kHz
Typ
Max
−89.1
−66.0
−88.9
−73.7
7.5
7.7
dBc
dBc
dBc
dBc
dBm
dBm
29.7
28.2
23.2
24.2
42.7
41.2
36.2
37.2
102
dBV rms
dBV rms
dBV rms
dBV rms
dBm
dBm
dBm
dBm
dB
+1
300
+6.25
1.2
50
75
100
200
1
6.2
6
3.25
−25
Single-ended, either output
Single-ended, either output
RL = 10 Ω differential
ENBON (enable high to output on)
ENBOFF (enable low to output off)
4.5
ENB = 5 V
TA = −40°C
TA = +85°C
ENB = GND
G = 24.08 dB, f = 100 kHz, no bypass capacitors
Rev. A | Page 4 of 28
Unit
2.5
+4
4.8
<0.1
2.5
77
200
200
5
24
21
27
50
120
−82
mV
µV/°C
V p-p
Ω
Ω
Ω
Ω
kΩ
kΩ
pF
V
+25
5.5
100
V
mV
V p-p
Ω
kΩ
mA
µs
µs
V
mA
mA
mA
µA
mW
dB
AD8432
ABSOLUTE MAXIMUM RATINGS
MAXIMUM POWER DISSIPATION
Table 2.
Parameter
Voltage
Supply Voltage
Input Voltage
Power Dissipation
Temperature
Operating Temperature
Storage Temperature
Package Glass Transition Temperature (TG)
Lead Temperature (Soldering, 60 sec)
Rating
5.5 V
0 V to VPS
120 mW
–40°C to +85°C
–65°C to +150°C
150°C
300°C
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.
The maximum safe power dissipation for the AD8432 is limited
by the associated rise in junction temperature (TJ) on the die. At
approximately 150°C, which is the glass transition temperature,
the properties of the plastic change. Even temporarily exceeding
this temperature limit may change the stresses that the package
exerts on the die, permanently shifting the parametric performance
of the amplifiers. Exceeding a temperature of 150°C for an
extended period can cause changes in silicon devices, potentially
resulting in a loss of functionality.
ESD CAUTION
THERMAL RESISTANCE
θJA is specified for the worst-case conditions, that is, a device
soldered in a circuit board for surface-mount packages. The θJA
value in Table 3 assumes a 4-layer JEDEC standard board with
zero airflow.
Table 3. Thermal Resistance1
Parameter
40-Lead LFCSP
1
θJA
57.9
θJC
11.2
θJB
35.9
ΨJT
1.1
Unit
°C/W
4-layer JEDEC board (2S2P).
Rev. A | Page 5 of 28
AD8432
INH1 1
18 GOL1
INL1 2
17 OPL1
AD8432
IND1 3
16 COM1
TOP VIEW
(Not to Scale)
COMM 4
15 COM2
GML2 12
GMH2 11
9
OPH2
GOH2 10
IND2 7
14 OPL2
13 GOL2
VPS2 8
INL2 5
INH2 6
NOTES
1. EXPOSED PAD MUST BE CONNECTED
TO GROUND.
Figure 2. Pin Configuration
Table 4. Pin Function Descriptions
Pin No.
1
2
3, 7
4
5
6
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
Mnemonic
INH1
INL1
IND1, IND2
COMM
INL2
INH2
VPS2
OPH2
GOH2
GMH2
GML2
GOL2
OPL2
COM2
COM1
OPL1
GOL1
GML1
GMH1
GOH1
OPH1
VPS1
ENB
EPAD
Description
LNA1 Noninverting Input.
LNA1 Inverting Input (AC-Coupled to Ground).
Integrated Input Clamping Back-to-Back Diodes.
Input Ground.
LNA2 Inverting Input (AC-Coupled to Ground).
LNA2 Noninverting Input.
5 V Supply.
Noninverting Output of LNA2.
Gain Setting Pin for LNA2.
Gain Setting Pin for LNA2.
Gain Setting Pin for LNA2.
Gain Setting Pin for LNA2.
Inverting Output of LNA2.
LNA2 Output Ground.
LNA1 Output Ground.
Inverting Output of LNA1.
Gain Setting Pin for LNA1.
Gain Setting Pin for LNA1.
Gain Setting Pin for LNA1.
Gain Setting Pin for LNA1.
Noninverting Output of LNA1.
5 V Supply.
Enable.
Exposed pad must be connected to ground.
Rev. A | Page 6 of 28
08341-002
20 GMH1
19 GML1
22 OPH1
21 GOH1
24 ENB
23 VPS1
PIN CONFIGURATION AND FUNCTION DESCRIPTIONS
AD8432
TYPICAL PERFORMANCE CHARACTERISTICS
VS = 5 V, TA = 25°C, RS = RIN = 50 Ω, RFB =150 Ω, CSH = 47 pF, RSH = 15 Ω, RL =500 Ω (per SE output), CL = 5 pF (per SE output),
G = 12.04 dB (single-ended input to differential output), f = 1 MHz, unless otherwise specified.
24
30
24
18
18
12
6
6
GAIN (dB)
GAIN (dB)
12
0
–6
0
–6
–12
–12
–24
= 24.08dB
= 21.58dB
= 18.06dB
= 12.04dB
–30
1
RIN UNTERMINATED
RIN = 200Ω
RIN = 100Ω
RIN = 50Ω
–18
10
100
1k
FREQUENCY (MHz)
–24
1
10
100
1k
FREQUENCY (MHz)
Figure 3. Small Signal Differential Gain vs. Frequency, RIN Unterminated
08341-056
G
G
G
G
08341-003
–18
Figure 6. Small Signal Frequency Response vs. RIN, G = 21.58 dB
24
30
21
24
18
18
15
12
9
GAIN (dB)
6
3
0
0
–6
–3
–12
–12
1
RIN UNTERMINATED
RIN = 200Ω
RIN = 100Ω
RIN = 50Ω
–18
10
100
500
FREQUENCY (MHz)
–24
08341-004
–9
1
10
100
1k
FREQUENCY (MHz)
Figure 4. Small Signal Frequency Response vs. RIN, G = 12.04 dB
08341-057
RIN UNTERMINATED
RIN = 200Ω
RIN = 100Ω
RIN = 50Ω
–6
Figure 7. Small Signal Frequency Response vs. RIN, G = 24.08 dB
24
30
18
24
12
18
12
GAIN (dB)
6
0
–6
6
0
–6
–12
–12
RIN UNTERMINATED
RIN = 200Ω
RIN = 100Ω
RIN = 50Ω
–18
–24
1
10
G
G
G
G
–18
100
1k
FREQUENCY (MHz)
08341-055
GAIN (dB)
6
Figure 5. Small Signal Frequency Response vs. RIN, G = 18.06 dB
= 24.08dB
= 21.58dB
= 18.06dB
= 12.04dB
–24
1
10
100
1k
FREQUENCY (MHz)
Figure 8. Differential Gain vs. Frequency, VOUT = 1 V p-p, RIN = 50 Ω
Rev. A | Page 7 of 28
08341-058
GAIN (dB)
12
AD8432
30
240
24
230
INPUT IMPEDANCE (Ω)
18
6
0
–6
220
210
200
190
180
–12
–18
–24
= 24.08dB
= 21.58dB
= 18.06dB
= 12.04dB
1
170
10
100
160
0.1
08341-011
G
G
G
G
1k
FREQUENCY (MHz)
Figure 9. Differential Gain vs. Frequency, VOUT = 2 V p-p, RIN = 50 Ω
G
G
G
G
= 24.08dB
= 21.58dB
= 18.06dB
= 12.04dB
1
10
FREQUENCY (MHz)
08341-031
GAIN (dB)
12
Figure 12. Input Impedance RIN vs. Frequency, 200 Ω Active Termination
55
10
54
INPUT IMPEDANCE (kΩ)
INPUT IMPEDANCE (Ω)
53
52
51
50
49
48
1
47
1
10
FREQUENCY (MHz)
0.1
0.1
10
3.5
3.0
OUTPUT IMPEDANCE (Ω)
110
105
100
95
G
G
G
G
= 24.08dB
= 21.58dB
= 18.06dB
= 12.04dB
2.5
2.0
1.5
1.0
0.5
1
FREQUENCY (MHz)
10
0
0.1
08341-030
INPUT IMPEDANCE (Ω)
1
Figure 13. Input Impedance RIN vs. Frequency, Unterminated
115
85
0.1
= 24.08dB
= 21.58dB
= 18.06dB
= 12.04dB
FREQUENCY (MHz)
Figure 10. Input Impedance RIN vs. Frequency, 50 Ω Active Termination
90
G
G
G
G
08341-032
= 24.08dB
= 21.58dB
= 18.06dB
= 12.04dB
1
10
FREQUENCY (MHz)
Figure 11. Input Impedance RIN vs. Frequency, 100 Ω Active Termination
Rev. A | Page 8 of 28
Figure 14. Output Impedance vs. Frequency
100
08341-033
45
0.1
G
G
G
G
08341-029
46
AD8432
1.00
0.1
0.1
1
10
100
FREQUENCY (MHz)
0.90
0.85
0.80
0.75
0.70
–50
10
100
OUTPUT VOLTAGE NOISE (nV/√Hz)
1k
SOURCE RESISTANCE (Ω)
70
90
90
12
G = 21.58dB
10
8
G = 18.06dB
6
4
G = 12.04dB
–30
–10
10
30
50
70
TEMPERATURE (°C)
Figure 16. Input-Referred Voltage Noise vs. Source Resistance (RS)
Figure 19. Output Voltage Noise vs. Temperature
1.6
f = 1MHz
G = 24.08dB
G = 21.58dB
10
G = 18.06dB
G = 12.04dB
1.2
1.0
0.8
0.6
0.4
0.2
1
1
10
100
1k
SOURCE RESISTANCE (Ω)
Figure 17. Output-Referred Voltage Noise vs. Source Resistance (RS)
0
0.01
G
G
G
G
= 24.08dB
= 21.58dB
= 18.06dB
= 12.04dB
0.1
1
10
FREQUENCY (MHz)
Figure 20. Input Voltage Noise vs. Frequency
Rev. A | Page 9 of 28
100
08341-221
INPUT VOLTAGE NOISE (nV/√Hz)
1.4
08341-035
OUTPUT-REFERRED VOLTAGE NOISE (nV/√Hz)
50
G = 24.08dB
14
2
–50
08341-036
INPUT-REFERRED VOLTAGE NOISE (nV/√Hz)
RS THERMAL
NOISE ALONE
100
30
16
f = 1MHz
1
10
Figure 18. Input Voltage Noise vs. Temperature
1
0.1
–10
TEMPERATURE (°C)
Figure 15. Output Impedance vs. Frequency in Disable Mode
10
–30
08341-037
1
0.95
08341-038
INPUT VOLTAGE NOISE (nV/√Hz)
10
08341-034
OUTPUT IMPEDANCE (kΩ)
100
AD8432
–40
20
G
G
G
G
16
HD2, 10MHz
HD2, 1MHz
HD3, 10MHz
HD3, 1MHz
MEASUREMENT
LIMIT
–50
–60
14
DISTORTION (dBc)
OUTPUT VOLTAGE NOISE (nV/√Hz)
18
= 24.08dB
= 21.58dB
= 18.06dB
= 12.04dB
12
10
8
6
–70
–80
–90
4
–100
0.1
1
10
100
FREQUENCY (MHz)
Figure 21. Output Voltage Noise vs. Frequency
0
–110
08341-222
0
0.01
0
1.0
1.5
2.0
2.5
3.0
3.5
4.0
4.5
VOUT (V p-p)
Figure 24. Harmonic Distortion vs. Differential Output Voltage, G = 12.04 dB
–40
LOW TONE
HIGH TONE
–10
0.5
08341-225
2
–50
–20
–60
DISTORTION (dBc)
IMD3 (dBc)
–30
–40
–50
–60
–70
–70
HD2, 10MHz
HD2, 1MHz
HD3, 10MHz
HD3, 1MHz
MEASUREMENT
LIMIT
–80
–90
–80
–100
1
10
100
FREQUENCY (MHz)
Figure 22. IMD3 vs. Frequency
50
–110
08341-223
–100
0
1.0
1.5
2.0
2.5
3.0
3.5
4.0
4.5
VOUT (V p-p)
Figure 25. Harmonic Distortion vs. Differential Output Voltage, G = 24.08 dB
–50
G = 24.08dB
G = 12.04dB
45
0.5
08341-226
–90
40
–60
DISTORTION (dBc)
30
25
20
15
–70
–80
HD2,
HD2,
HD3,
HD3,
5
0
1
10
FREQUENCY (MHz)
100
Figure 23. Output Third-Order Intercept vs. Frequency
10MHz,
10MHz,
10MHz,
10MHz,
2V p-p
1V p-p
2V p-p
1V p-p
–90
0
5
10
15
CL (pF)
20
25
08341-227
10
08341-224
OIP3 (dBm)
35
Figure 26. Harmonic Distortion at 10 MHz vs. Capacitive Load (CL),
G = 12.04 dB
Rev. A | Page 10 of 28
AD8432
–50
–50
HD2,
HD2,
HD3,
HD3,
2V p-p
1V p-p
2V p-p
1V p-p
HD2,
HD2,
HD3,
HD3,
–55
DISTORTION (dBc)
–70
–80
–90
10MHz,
10MHz,
10MHz,
10MHz,
2V p-p
1V p-p
2V p-p
1V p-p
–60
–65
–70
–100
0
5
10
15
20
25
CL (pF)
–75
08341-269
–110
0
200
400
600
800
1000 1200 1400 1600 1800 2000
RL (Ω)
Figure 27. Harmonic Distortion at 1 MHz vs. Capacitive Load (CL),
G = 12.04 dB
08341-229
DISTORTION (dBc)
–60
1MHz,
1MHz,
1MHz,
1MHz,
Figure 30. Harmonic Distortion at 10 MHz vs. Resistive Load (RL),
G = 12.04 dB
–60
–40
–50
HD2,
HD2,
HD3,
HD3,
–65
1MHz,
1MHz,
1MHz,
1MHz,
1V p-p
2V p-p
2V p-p
1V p-p
–60
DISTORTION (dBc)
DISTORTION (dBc)
–70
–70
–80
–90
–75
–80
–85
2V p-p
1V p-p
2V p-p
1V p-p
–90
–100
0
5
10
15
20
25
30
35
CL (pF)
–95
0
200
400
600
800
1000 1200 1400 1600 1800 2000
RL (Ω)
08341-271
10MHz,
10MHz,
10MHz,
10MHz,
08341-228
HD2,
HD2,
HD3,
HD3,
Figure 31. Harmonic Distortion at 1 MHz vs. Resistive Load (RL),
G = 12.04 dB
Figure 28. Harmonic Distortion at 10 MHz vs. Capacitive Load (CL),
G = 24.08 dB
–50
–60
–55
–70
DISTORTION (dBc)
–80
–90
–100
–65
–70
–75
–80
–85
HD2,
HD2,
HD3,
HD3,
–120
0
5
10
15
20
25
1MHz,
1MHz,
1MHz,
1MHz,
30
1V p-p
2V p-p
2V p-p
1V p-p
HD2,
HD2,
HD3,
HD3,
–90
35
CL (pF)
Figure 29. Harmonic Distortion at 1 MHz vs. Capacitive Load (CL),
G = 24.08 dB
–95
0
200
400
600
800
10MHz,
10MHz,
10MHz,
10MHz,
2V p-p
1V p-p
2V p-p
1V p-p
1000 1200 1400 1600 1800 2000
RL (Ω)
Figure 32. Harmonic Distortion at 10 MHz vs. Resistive Load (RL),
G = 24.08 dB
Rev. A | Page 11 of 28
08341-230
–110
08341-270
DISTORTION (dBc)
–60
AD8432
–60
–70
HD2,
HD2,
HD3,
HD3,
–65
1MHz,
1MHz,
1MHz,
1MHz,
1V p-p
2V p-p
2V p-p
1V p-p
–75
–80
–85
CROSSTALK (dB)
DISTORTION (dBc)
–70
–75
–80
–90
–95
–100
–105
–85
–110
–90
0
200
400
600
800
1000 1200 1400 1600 1800 2000
RL (Ω)
–120
0.1
1
10
100
FREQUENCY (MHz)
Figure 36. Channel Crosstalk vs. Frequency
Figure 33. Harmonic Distortion at 1 MHz vs. Resistive Load (RL),
G = 24.08 dB
–50
1V/DIV
–70
–90
HD2,
HD2,
HD3,
HD3,
10MHz,
10MHz,
10MHz,
10MHz,
2V p-p
1V p-p
2V p-p
1V p-p
–100
2
4
6
8
10
12
14
16
18
GAIN (V/V)
100ns/DIV
Figure 34. Harmonic Distortion at 10 MHz vs. Gain
–50
HD2,
HD2,
HD3,
HD3,
Figure 37. Overdrive Recovery, G = 12.04 dB
2V p-p
1V p-p
2V p-p
1V p-p
1V/DIV
–70
–80
–90
–110
2
4
6
8
10
12
14
16
GAIN (V/V)
18
Figure 35. Harmonic Distortion at 1 MHz vs. Gain
100ns/DIV
Figure 38. Overdrive Recovery, G = 24.08 dB
Rev. A | Page 12 of 28
08341-013
–100
08341-273
DISTORTION (dBc)
–60
1MHz,
1MHz,
1MHz,
1MHz,
08341-132
–80
08341-231
DISTORTION (dBc)
–60
08341-232
–95
08341-272
–115
AD8432
CL = 5pF
CL = 10pF
CL = 15pF
CL = 20pF
CL = 30pF
G = 24.08dB
50mV/DIV
200mV/DIV
G = 21.58dB
G = 18.06dB
10ns/DIV
08341-017
08341-014
G = 12.04dB
10ns/DIV
Figure 39. Small Signal Transient Response vs. Gain, VIN = 100 mV p-p
Figure 42. Small Signal Transient Response vs. Capacitive Load (CL),
G = 24.08 dB
10ns/DIV
08341-018
08341-015
50mV/DIV
100mV/DIV
RL = 499Ω
RL = 249Ω
RL = 24.9Ω
RL = 15Ω
RL = 10Ω
10ns/DIV
Figure 40. Small Signal Transient Response, G = 12.04 dB
Figure 43. Small Signal Transient Response vs. Resistive Load (RL),
G = 12.04 dB
CL = 15pF
CL = 10pF
CL = 5pF
10ns/DIV
Figure 41. Small Signal Transient Response vs. Capacitive Load (CL),
G = 12.04 dB
08341-019
10ns/DIV
08341-016
50mV/DIV
50mV/DIV
RL = 499Ω
RL = 249Ω
RL = 24.9Ω
RL = 15Ω
RL = 10Ω
Figure 44. Small Signal Transient Response vs. Resistive Load (RL),
G = 24.08 dB
Rev. A | Page 13 of 28
AD8432
CL = 30pF
CL = 20pF
CL = 15pF
CL = 10pF
CL = 5pF
G = 18.06dB
08341-020
50mV/DIV
500mV/DIV
G = 21.58dB
G = 24.08dB
10ns/DIV
08341-023
G = 12.04dB
10ns/DIV
Figure 45. Small Signal Transient Response vs. Gain, VOUT = 200 mV p-p
Figure 48. Large Signal Transient Response vs. Capacitive Load (CL),
G = 24.08 dB
RL = 499Ω
RL = 249Ω
RL = 24.9Ω
RL = 15Ω
G = 24.08dB
500mV/DIV
500mV/DIV
G = 21.58dB
G = 18.06dB
10ns/DIV
08341-024
08341-021
G = 12.04dB
10ns/DIV
Figure 46. Large Signal Transient Response vs. Gain, VIN = 125 mV p-p
Figure 49. Large Signal Transient Response vs. Resistive Load (RL),
G = 12.04 dB
RL = 499Ω
RL = 249Ω
RL = 24.9Ω
RL = 15Ω
RL = 10Ω
10ns/DIV
Figure 47. Large Signal Transient Response vs. Capacitive Load (CL),
G = 12.04 dB
08341-025
10ns/DIV
08341-022
500mV/DIV
500mV/DIV
CL = 20pF
CL = 15pF
CL = 10pF
CL = 5pF
Figure 50. Large Signal Transient Response vs. Resistive Load (RL),
G = 24.08 dB
Rev. A | Page 14 of 28
AD8432
G = 12.04dB
140
G = 18.06dB G = 21.58dB
G = 24.08dB
500mV/DIV
SUPPLY CURRENT (µA)
120
100
80
60
40
10ns/DIV
0
–60
–40
–20
0
20
40
60
80
100
TEMPERATURE (°C)
Figure 51. Large Signal Transient Response vs. Gain, VOUT = 2 V p-p
Figure 54. Supply Current vs. Temperature in Disable Mode
–20
ENB
5V/DIV
–30
1
PSRR (dB)
–40
–50
–60
OUTPUT
50mV/DIV
–70
2
–80
0.1
1
10
100
FREQUENCY (MHz)
TIME (100µs/DIV)
08341-252
–100
0.01
08341-248
G = 24.08dB
NO BYPASS CAPS
–90
Figure 55. Small Signal Enable Response
Figure 52. PSRR vs. Frequency
30
ENB
5V/DIV
1
26
OUTPUT
500mV/DIV
24
2
20
–60
–40
–20
0
20
40
60
TEMPERATURE (°C)
80
100
TIME (100µs/DIV)
Figure 56. Large Signal Enable Response
Figure 53. Supply Current vs. Temperature
Rev. A | Page 15 of 28
08341-251
22
08341-027
SUPPLY CURRENT (mA)
28
08341-028
08341-026
20
AD8432
TEST CIRCUITS
0.1µF
RFB
1MHz
(10MHz LPF)
INH
OPH
AD8432
0.1µF
INL
0.1µF
1.7MHz
(10.7MHz)
G=1
RL
50Ω
LP
56.2Ω
AD8130
LNA1
CSH
HP
475Ω
RL
50Ω
08341-046
0.1µF
OPL
INH
INL
RSH
1MHz
(10MHz)
SPECTRUM
ANALZYER
DUAL FILTER
0.1µF
Figure 57. Harmonic Distortion vs. Resistive Load (RL) Measurements
0.1µF
RFB
DUAL FILTER
SPECTRUM
ANALYZER
LP 50Ω
1MHz
(10MHz LPF)
RSH
OPL
INL
OPH
0.1µF
CL
26.1Ω
487Ω
HP
1:1
IN
LNA1
1.7MHz
(10.7MHz)
CL
26.1Ω
RL
Figure 58. Harmonic Distortion vs. Capacitive Load (CL) Measurements
NETWORK
ANALYZER
50Ω
OUT
50Ω
0.1µF
RSH
499Ω
0.1µF
INH
OPL
AD8432
0.1µF
5pF
DIFF
PROBE
0.1µF
OPH
INL
CSH
IN
0.1µF
499Ω
LNA1
08341-047
RFB
5pF
Figure 59. Frequency Response Measurements
SPECTRUM
ANALYZER
0.1µF
0.1µF
INH
OPL
INL
OPH
50Ω
1kΩ
0.1µF
AD8432
LNA1
50Ω
0.1µF
AD8432
CSH
487Ω
0.1µF
1kΩ
AD8129
G = 10
Figure 60. Voltage Noise Measurements
Rev. A | Page 16 of 28
08341-048
1MHz
(10MHz)
0.1µF
INH
08341-049
0.1µF
AD8432
5pF
0.1µF
RFB
10MHz
X MULTIPLIER
0.1µF
INH
OPL
0.1µF
499Ω
DIFF
PROBE
OSCILLOSCOPE
CH1
RSH
Y
INL
CSH
OPH
AD8432
1MHz
LNA1
0.1µF
499Ω
5pF
08341-050
0.1µF
Figure 61. Overdrive Recovery Measurements
499Ω
50Ω
0.1µF
OUT
RSH
0.1µF
INH
OPL
INL
OPH
CSH
0.1µF
5pF
499Ω
AD8432
0.1µF
LNA1
08341-051
NETWORK
ANALYZER
5pF
0.1µF
RFB
Figure 62. Input Impedance vs. Frequency Measurements
0.1µF
RFB
NETWORK
ANALYZER
0.1µF
0.1µF
INH
RSH
INL
CSH
OPH
0.1µF
AD8432
499Ω
LNA1
08341-052
0.1µF
50Ω
OPL
Figure 63. Output Impedance vs. Frequency Measurements
RFB
0.1µF
SPECTRUM
ANALYZER
INH1
OPL1
0.1µF
+IN
1kΩ
RS
INL1
0.1µF
AD8432
OUT
50Ω
–IN
OPH1
0.1µF
1kΩ
AD8129
G = 10
LNA1
Figure 64. Noise Figure Measurements
Rev. A | Page 17 of 28
08341-054
0.1µF
AD8432
THEORY OF OPERATION
LOW NOISE AMPLIFIER (LNA)
differential gain of G = 12.04 dB, the maximum input voltage
allowed is 1.2 V p-p.
The AD8432 is a dual-channel, ultralow noise amplifier with
integrated pin-strappable, gain-setting resistors. The resistors
can be externally connected to achieve differential gains of
12.04 dB, 18.06 dB, 21.58 dB, and 24.08 dB (×4, ×8, ×12, and
×16, respectively). A simplified schematic of an LNA is shown
in Figure 65.
Clamping the inputs ensures quick recovery from large input
voltages. The input back-to-back diodes, which are integrated
inside the die (IND1 and IND2), should be used for the lowest gain
configuration (12.04 dB) to protect the input from overdriving.
They should be connected after the source resistance or before
the INH coupling capacitor.
The LNA is driven with a single-ended input and measured
differentially at the output. The inverting input INL must be
ac-coupled to ground through a capacitor for proper operation.
The LNA cannot be driven differentially due to the asymmetry
of the internal gain setting resistors. The gain from the inverting
input INL to the single-ended output (OPH or OPL) does not
match the gain from the noninverting input INH to the singleended output.
The use of a fully differential topology and negative feedback
minimizes distortion. A differential signal enables smaller swings at
each output, which results in reduction of third-order distortion.
The AD8432 is a voltage feedback amplifier. Due to gain bandwidth product (GBW), a decrease in bandwidth should be
expected as the gain increases. Table 5 displays the values of the
−3 dB bandwidth for each gain with unterminated input
impedance.
The AD8432 inputs have a dc bias voltage of 3.25 V, which is
generated internally. The inputs must be ac-coupled through a
series capacitor to maintain the dc bias level of the inputs. Likewise,
the AD8432 outputs have a dc bias voltage of 2.5 V. An ac coupling
capacitor in series with each single-ended output is recommended
to prevent improper loading of the outputs. The AD8432 inputs
have a dc bias voltage of 3.25 V, which is generated internally.
The inputs must be ac-coupled through a series capacitor to
maintain the dc bias level of the inputs (see CINL and CINH
in Figure 65).
GAIN SETTING TECHNIQUE
Pin strapping is used to set the gain of the amplifier. Gain setting
resistors are integrated in the LNA and are accessible externally
through the GOH, GMH, GML, and GOL pins. By externally
shorting these pins, and thereby shorting or connecting the
internal resistors, the AD8432 can be configured for four different
gains. Table 5 shows which pins must be connected to achieve
the desired gain.
The AD8432 supports a differential output voltage of 4.8 V p-p
for the common-mode output voltage of 2.5 V. Therefore, for a
CFB
RFB
VPS
I
I
OPL
OPH
INL
Q1
Q2
CINH
RSH
INH
RG4
48Ω
RG3
24Ω
RG2
12Ω
RG1
12Ω
RG7
48Ω
RG6
24Ω
RG5
24Ω
CINL
CSH
RS
GND
GOH
GMH
I
I
GND
GML
GOL
GND
Figure 65. Simplified Schematic of LNA
Rev. A | Page 18 of 28
08341-039
VS
AD8432
Table 5. Gain Setting Using a Pin-Strapping Technique and −3 dB Bandwidth for Each Gain Configuration
Differential
Gain (dB)
12.04
Single
Gain (dB)
6.02
−3 dB
BW (MHz)
200
RG1 (Ω)
12
RG2 (Ω)
12
18.06
12.04
90
12
12
21.58
15.56
50
12
12
24.08
18.06
32
12
12
RG3 (Ω)
Connect
GMH to GOH
24
Connect
GMH to GOH
24
RG4 (Ω)
Connect
GOH to OPH
Connect
GOH to OPH
48
RG5 (Ω)
24
48
24
The single-ended gain from INH to OPH (see Figure 65) is
defined as
48
INH
LNA
VOUT
VIN
UNTERMINATED
RIN
RS
INH
LNA
R + RG6 + RG7
= − G5
RG1
VOUT
RS
VIN
RESISTIVE
TERMINATION
The values of the seven gain resistors were chosen so that both
single-ended gains are equal. For example, to set a gain of
12.04 dB (G = ×4) differentially, the gain from INH to each
output (OPH, OPL) should be 6.02 dB (G = ×2).
RFB
RIN
RS
INH
LNA
VOUT
VIN
INH to OPH: For RG1 = RG2 = RG, then
ACTIVE
IMPEDANCE MATCH
R G1 + R G2 2 × RG
=
=2
R G1
RG
Figure 66. Input Resistance Matching
To achieve this active impedance match, connect a feedback
resistor, RFB, between the INH and OPL (see Figure 66). RIN is
given in Equation 1, where G/2 is the single-ended gain.
INH to OPL: For RG1 = RG and RG5 = 2 × RG, then
G OPL − INH = −
Connect
GML to GOL
24
RIN
R + RG2 + RG3 + RG4
= G1
RG1
G OPH − INH =
24
RS
The single-ended gain from INH to OPL is defined as
G OPL − INH
24
RG7 (Ω)
Connect
GOL to OPL
Connect
GOL to OPL
48
08341-009
G OPH − INH
RG6 (Ω)
Connect
GML to GOL
24
2 × RG
RG5
=−
= −2
RG1
RG
R IN =
ACTIVE INPUT RESISTANCE MATCHING
The AD8432 reduces noise and optimizes signal power transfer
by using active input termination to perform signal source
resistance matching.
The primary purpose of input impedance matching is to optimize
the input signal power transfer. With resistive termination, the
input noise increases due to the thermal noise of the terminating
resistor and the increased contribution of the input voltage
noise generator of the LNA. With active impedance matching,
however, the contributions of both are smaller than they are for
resistive termination by a factor of 1/(1 + ½ LNA) gain. The
noise figure (NF) for the three terminating schemes is shown in
Figure 67.
R FB
G
1+
2
(1)
In addition, to further reduce the input resistance, there is an
internal resistance of 6.2 kΩ in parallel with the source resistance,
such that
R IN =
R FB
R
G INTERNAL
1+
2
(2)
Equation 3 should be used to calculate RFB accurately for a desired
input resistance and single-ended gain. Refer to Table 6 for
calculated results for RFB for several input resistance and gain
combinations.
⇒ R FB
Rev. A | Page 19 of 28
G
R IN 1 + 
2

=
, R INTERNAL = 6.2 kΩ
R IN
1−
R INTERNAL
(3)
AD8432
8
The user must determine the level of matching accuracy desired
and adjust RFB accordingly. The RFB and CFB network presents a
load to OPL that OPH does not see. The user can add an identical
load on OPH to improve slightly the distortion caused by this
imbalance.
7
NOISE FIGURE (dB)
6
RESISTIVE TERMINATION
(RS = RIN)
5
4
There is a feedback capacitor (CFB) in series with RFB (see Figure
65) because the dc levels of the positive output and the positive
input are different. At higher frequencies, the value of the
feedback capacitor must be considered.
ACTIVE IMPEDANCE
MATCH
3
2
UNTERMINATED
1
(SIMULATED RESULTS)
100
1k
08341-267
0
50
RS (Ω)
Figure 67. Noise Figure vs. RS for Resistive, Active Match, and
Unterminated Inputs
18
16
NOISE FIGURE (dB)
14
The unterminated bandwidth (RFB = ∞) is 200 MHz. The AD8432
has a low input-referred voltage noise of 0.85 nV/√Hz at the
lowest gain, 12.04 dB (unterminated configuration). To achieve
such low noise, the dual amplifier consumes 24 mA, resulting in
a power consumption of 120 mW.
RIN = 1kΩ
RIN = 200Ω
RIN = 100Ω
RIN = 75Ω
RIN = 50Ω
RIN = UNTERMINATED
12
10
8
6
4
2
(SIMULATED RESULTS)
100
1k
RS (Ω)
08341-268
0
50
Figure 68. Noise Figure vs. RS for Various Values of RIN, Actively Matched
Table 6. Feedback Resistance for Several RIN and Gain Combinations
Desired RIN (Ω)
50
75
100
200
1k
50
100
50
100
50
100
Differential Gain (V/V)
4
4
4
4
4
8
8
12
12
16
16
Single-Ended Gain,
G/2 (V/V)
2
2
2
2
2
4
4
6
6
8
8
Exact RFB (Ω),
Equation 2
151.2
227.8
304.9
620
3.58 k
252
508.2
352.9
711.5
453.7
914.8
Rev. A | Page 20 of 28
RFB (Ω), 1% Standard Value
150
226
301
619
3.57 k
250
511
357
715
453
909
Actual RIN (Ω),
Equation 2
49.6
74.4
98.7
199.7
998.4
49.6
100.5
50.6
100.5
49.9
99.4
AD8432
APPLICATIONS INFORMATION
The unterminated input impedance of the AD8432 is 6.2 kΩ.
Any input resistance between 50 Ω and 6.2
kΩ can be synthesized
using active impedance matching.
The AD8432 LNA provides precision gain and ultralow noise
performance with minimal external components. Because it is
a high performance part, care must be taken to ensure that it is
configured optimally to attain the best performance and dynamic
range for the system.
At the lowest gain (12.04 dB), the gain response exhibits some
peaking at higher frequencies. A resistor-capacitor shunt network (RC) at the input (see RSHx and CSHx in Figure 69) is
recommended to reduce gain peaking and enhance stability at
higher frequencies.
TYPICAL SETUP
The internal bias circuitry of the AD8432 sets the input bias
voltage at 3.25 V and the output bias voltage at 2.5 V. It is important
to ac couple the inputs through a capacitor to maintain the internal
dc bias levels. When active input termination is used (RFB), a
decoupling capacitor (CFB) is required to isolate the input and
output bias voltages of the LNA. A typical value for CFB is 0.1 µF, but
a smaller value capacitor is more appropriate at higher frequencies.
Table 7 shows the recommended values of RFB, CSH, and RSH for
all four gains and several input impedance combinations. The
values for the CSH and RSH network are determined empirically
and can be customized as needed to optimize performance. As
RIN increases, the value of CSH diminishes, and for higher input
impedance values, no capacitor may be required.
CFB1
0.1µF
RFB1
FB
120nH
G = 12dB
0.1µF
0.1µF
ENB
VPS1
COMM
VPS2
BIAS
FB
120nH
0.1µF
IN1
RSH1
15Ω
CSH1
47pF
INH1
IND1
LNA1
0.1µF
IN2
RSH2
15Ω
CSH2
47pF
OPL1
INL1
GMH1
GOH1
GOL1
GML1
INH2
IND2
OPH2
0.1µF
FB
120nH
LNA2
INL2
0.1µF
0.1µF
OPH1
OPL2
GMH2
GOH2
GOL2
GML2
OUT1+
RL
CL
OUT1–
0.1µF
0.1µF
OUT2+
RL
CL
OUT2–
0.1µF
RFB2
08341-040
AD8432
CFB2
0.1µF
Figure 69. Typical AD8432 Setup, G = 12.04 dB
Rev. A | Page 21 of 28
AD8432
Table 7. External Component Selections for Common Input Impedance
RIN (Ω)
50
75
100
200
1k
Unterminated, RS = 50 Ω
Unterminated, RS = 0 Ω
Gain (dB)
12
18
21
24
12
18
21
24
12
18
21
24
12
18
21
24
12
18
21
24
12
18
21
24
12
18
21
24
RFB (Ω)
150
249
357
453
226
383
536
681
301
511
715
909
619
1.02 k
1.43 k
1.87 k
3.57 k
5.9 k
8.25 k
10.7 k
∞
∞
∞
∞
∞
∞
∞
∞
CSH (pF)
47
30
None
None
36
None
None
None
30
None
None
None
18
None
None
None
10
None
None
None
None
None
None
None
None
None
None
None
Rev. A | Page 22 of 28
RSH (Ω)
15
15
None
None
15
None
None
None
15
None
None
None
15
None
None
None
10
None
None
None
None
None
None
None
None
None
None
None
−3 dB BW (MHz)
176
116
117
87
167
144
100
72
164
134
90
63
164
116
74
51
160
99
61
43
178
95
59
40
210
96
55
38
AD8432
I/Q DEMODULATION FRONT END
4LOP and 4LON pins of the AD8339, has a frequency 4× that of
the RF inputs. The AD8339 downconverts the RF signals,
generates quadrature, and phase-shifts the resultant I and Q
signals.
The AD8432 low noise amplifiers can be used to drive the
differential RF inputs of the dual AD8333 or the quad AD8339
I/Q demodulators. The primary application for the AD8339 is
phased array beamforming in medical ultrasound, specifically
in CW Doppler processing. Other applications include phased
array radar and smart antennas for mobile communications.
The I and Q outputs of the AD8339 are current outputs. A
transimpedance amplifier, such as the AD8021, processes the
outputs and performs several functions, including the following:
•
•
•
AD8021
Q1
0.1µF
20Ω
RF1P
787Ω
Q1OP
2.2nF
AD8339
AD8432
RF1N
In beamforming applications, the I and Q outputs of a number
of receiver channels are summed, which increases the system
dynamic range by 10 log10 (N), where N is the number of
channels being summed. The external RC feedback network of
the AD8021 is a 100 kHz low-pass filter as shown in Figure 70.
See the AD8333 and AD8339 datasheets for more details on
implementing I/Q demodulators.
2.2nF
I1OP
20Ω
787Ω
0.1µF
4LO
08341-041
I1
0.1µF
AD8021
Current-to-voltage conversion
Summation amplifier for multiple channels
Active low-pass filter
Figure 70. Block Diagram of AD8432 and AD8339 Application for
Ultrasound Beamforming
Evaluation boards are available for the AD8432 and the AD8339
to facilitate system level design and testing. A detailed reference
schematic of the setup is shown in Figure 71. The AD8432 is
shown in this configuration with a gain of 12.04 dB, with
unterminated inputs. If active termination is preferred, use an
RFB and CFB network as discussed in the Theory of Operation
section. The IND1/IND2 clamping diodes can be connected to
IN1/IN2 to protect the LNA input from being overdriven.
Because of its low output noise and low distortion, the AD8432
ensures minimal degradation in dynamic range while amplifying
the RF input signal. At the lowest gain of 12.04 dB, the AD8432
contributes only 3.4 nV/√Hz output voltage noise.
Figure 70 shows a simplified block diagram of one channel of
the AD8432 driving the AD8339. The AD8432 outputs can be
connected directly to the AD8339 RF inputs through 20 Ω
resistors. A differential clock signal, 4LO, which is applied to the
4LO
0.1µF
0.1µF
0.1µF
IN1
RSH1
15Ω
CSH1
47pF
VPS1
VPS2
BIAS
INH2
RSH2
15Ω
CSH2
47pF
IND2
VPOS
VNEG
4LOP
2 7
OPH1
20Ω RF1P
Q1OP
OPL1
20Ω RF1N
I1OP
0.1µF
Q1 + Q2
3 4
0.1µF
+5V
OPL2
GMH2
GOH2
GOL2
GML2
INL2
0Ω
+
−5V
OPH2
LNA2
6
AD8021
GMH1
GOH1
GOL1
GML1
0.1µF
0.1µF
787Ω
0.1µF
–
LNA1
INL1
IN2
0.1µF
2.2nF
COMM
INH1
IND1
0.1µF
+5V
20Ω RF2P
787Ω
Q2OP
0.1µF
20Ω RF2N
2.2nF
I2OP
2 7
–
AD8339
6
AD8021
0Ω
I1 + I2
+
G = –1.3dB
AD8432
3 4
LPF
fC = 100kHz
G = 12dB
0.1µF
−5V
Figure 71. Schematic of the AD8432 (G = 12.04 dB) and AD8339 Application for Ultrasound Beamforming
Rev. A | Page 23 of 28
08341-043
ENB
−5V
+5V
AD8432
DIFFERENTIAL-TO-SINGLE-ENDED CONVERSION
A transformer or balun can also be used to convert the differential
output of the AD8432 to a single-ended output. Transformers
have lower distortion; however, care must be taken to properly
match the impedance of the transformer. The test circuit for
distortion measurements in Figure 58 uses an ADTT1-1
transformer to perform differential-to-single-ended conversion.
Some applications require the low noise and high dynamic
range of the AD8432; however, they may also require a singleended output, rather than a differential output. The AD8129
or AD8130 differential receiver amplifier can be used for the
differential-to-single-ended conversion of the AD8432 output,
as shown in Figure 72.
The AD8129 is a low noise, high gain (10 or greater) amplifier
intended for applications over very long cables, where signal
attenuation is significant. The AD8130 is stable at a gain of 1
and can be used for applications where lower gains are required.
The AD8129 and AD8130 have user-adjustable gain, set by the
ratio of two resistors, to help compensate for losses in the
transmission line.
0.1µF
0.1µF
0.1µF
IN1
VPS1
COMM
INL1
0.1µF
G = 12 dB
+VS
AC-COUPLING CAPS
SERIES 20Ω
RESISTORS IF DRIVING (AD8432 HAS 2.5V
OUTPUT BIAS)
HIGH CAP LOAD
INH1
IND1
RSH1
15Ω
CSH1
47pF
VPS2
BIAS
LNA1
GMH1
GOH1
GOL1
GML1
OPH1
20Ω
0.1µF
OPL1
20Ω
0.1µF
499Ω
1
8
499Ω
4
5
+
–
+
–
7
6
VOUT1
2
AD8130
499Ω RESISTORS PROVIDE
BIAS CURRENT PATH AND
TERMINATION IF NECESSARY
–VS
Figure 72. AD8432 Differential-to-Single-Ended Conversion Using the AD8129/AD8130 with Unity Gain
Rev. A | Page 24 of 28
08341-044
ENB
AD8432
EVALUATION BOARD
Figure 73 shows the AD8432 evaluation board, and the schematic
diagram is shown in Figure 74. Using the board is a convenient
and fast way to verify system design and assess the performance of
the AD8432 under user-specific operating conditions. The
board provides access to all LNA inputs, outputs, and gain setting
pins. The board is shipped in a typical G = 12.04 dB configuration
but is designed to allow customization of the setup as required.
The AD8432-EVALZ requires a single 5 V power supply. An
on-board switch (S1) allows VPS to drive the enable (ENB) input.
GAIN SETTING
Table 8 outlines the resistors or headers that must be installed or
shorted for each gain configuration.
Table 8. Gain Setting Using Resistors or Headers
R1
R2
R3
R4
1
LNA2
R9
W9
R10
W10
R11
W11
R12
W12
4
X1
X1
X1
X1
X = shorting the indicated header or resistor.
08341-045
Headers (W5 to W12) are provided across the gain setting pins
and can be shorted using jumpers to allow gain setting quickly
and easily. Alternately, it is recommended to short the gain setting
pins using surface-mount (0402), 0 Ω resistors (R1 to R4, R9 to
R12) that eliminate the small parasitic capacitances from longer
trace lengths to the headers. As shipped, the evaluation board is
configured for G = 12.04 dB with these 0 Ω resistors.
LNA1
W5
W6
W7
W8
Figure 73. Evaluation Board
Rev. A | Page 25 of 28
Gain (V/V)
8
12
X1
X1
X1
X1
16
Figure 74. Schematic
Rev. A | Page 26 of 28
7 IND2
VPS2
9 OPH2
8 VPS2
L4
CFB2
0.1µF 120nH FB
DNI
OPH2
VPOS
W4
12 GML2
W9 W10
GOH2 GMH2
R9 R10
0Ω 0Ω
10 GOH2
C4
0.1µF
PIN 0
EXPOSED PADDLE
(TIED TO GND)
TOP VIEW
(Not to Scale)
AD8432
11 GMH2
RFB2
DNI
C6
0.1µF
ENB 24
RSH2
15Ω
CSH2
47pF
INH2 6
INL2 5
COMM 4
VPS1 23
INH2
COMM
INL2
IND1 3
INL1 2
INH1 1
R2
0Ω
GML1 19
W2
INL1
C1
0.1µF
RSH1
15Ω
OPH1 22
C2
0.1µF
CSH1
47pF
R1
0Ω
R3
0Ω
W7
GML2 W11
R11
0Ω
13 GOL2
14 OPL2
15 COM2
16 COM1
17 OPL1
18 GOL1
GOH1 GMH1
W5 W6
GML1
OPH1
GND
BANANA
GND JACK
GOH1 21
PRB2
PRB1
S1
C3
ENB
0.1µF
VPS1
C5
PIN 1
0.1µF INH1 IDENTIFIER
ENABLE
DISABLE
+5V
L3
120nH FB
W3
VPOS
GMH1 20
L2
IN2 120nH FB
W1
L1
IN1 120nH FB
GND1 GND2 GND3
RFB1
DNI
CFB1
0.1µF
DNI
BANANA
JACK VPOS
GOL2
R12
0Ω
COM1
R4
0Ω
GOL1
W12
OPL2
OPL1
W8
R13
DNI
PRB4
R14
DNI
R6
DNI
PRB3
R5
DNI
RL3
DNI
RL4
DNI
RL2
DNI
RL1
DNI
CL3 C13
DNI 0.1µF
DNI
CL4
DNI
C14
0.1µF
DNI
CL2 C10
DNI 0.1µF
DNI
CL1
DNI
GND4 GND5 GND6
C11
0.1µF
DNI
C12
0.1µF
DNI
C8
0.1µF
DNI
C7
0.1µF
DNI
C9
0.1µF
DNI
R15
453Ω
DNI
6
T2 4
2
R16
453Ω
DNI
R8
453Ω
DNI
6
T1 4
2
R7
453Ω
DNI
TEST POINT
AD8432 EVALUATION BOARD
SCHEMATIC
OPH2
R18
0Ω VOUT2
3 DNI
1
OPL2
OPL1
R17
0Ω VOUT1
3 DNI
1
OPH1
AD8432
SCHEMATIC
08341-042
AD8432
POWER SUPPLY
OUTPUT
The AD8432 should be powered by a single 5 V supply connected
to the VPOS terminal. Separate supplies can be used for VPS1,
VPS2, and ENB, or they can all be tied to VPOS by shorting
the W3 and W4 headers and the S1 switch. Ferrite beads and
decoupling capacitors are installed for isolation, protection, and
power supply noise reduction.
The AD8432 evaluation board provides the space to configure
the output loading conditions required by the user, by populating
the given footprints (for example, RL1, RL2, C7, and C8). SMA
connectors are available at the outputs, and space for a transformer
is also available for differential-to-single-ended conversion.
INPUT TERMINATION
Active input impedance matching can be realized by installing
a feedback resistor (RFB), the value of which is determined by
the gain and source impedance, as described in the Theory of
Operation section. CFB provides the necessary ac coupling
between the input and output when using active termination;
a 0.1 µF capacitor value is recommended. The RFB and CFB network
presents a load to OPL, and an equivalent load at OPH can be
used to balance the differential output.
The 4-pin headers, PRB3 and PRB4, are placed close to the AD8432,
and they provide a way for monitoring the differential output or
the single-ended output using a high impedance differential probe.
The two inner pins of the headers are connected to OPL/OPH,
and the two outer pins of the headers are connected to ground.
There are several footprints provided to install ac coupling
capacitors at the outputs (C7 to C14). The AD8432 outputs are
biased internally at 2.5 V. To maintain the dc bias level, use coupling
capacitors between the outputs and the load.
Input clamping diodes (IND1 and IND2) can be connected to the
inputs by shorting the connection on the W1 and W2 headers.
The diodes provide overvoltage protection to the input and
enable faster overdrive recovery times, especially at the lowest
gain (12.04 dB).
Rev. A | Page 27 of 28
AD8432
OUTLINE DIMENSIONS
PIN 1
INDICATOR
4.10
4.00 SQ
3.90
0.30
0.25
0.18
0.50
BSC
PIN 1
INDICATOR
24
19
18
1
2.65
2.50 SQ
2.45
EXPOSED
PAD
TOP VIEW
0.80
0.75
0.70
0.50
0.40
0.30
13
12
0.25 MIN
BOTTOM VIEW
0.05 MAX
0.02 NOM
COPLANARITY
0.08
SEATING
PLANE
6
7
FOR PROPER CONNECTION OF
THE EXPOSED PAD, REFER TO
THE PIN CONFIGURATION AND
FUNCTION DESCRIPTIONS
SECTION OF THIS DATA SHEET.
COMPLIANT TO JEDEC STANDARDS MO-220-WGGD.
112108-A
0.20 REF
Figure 75. 24-Lead Lead Frame Chip Scale Package [LFSCP_WQ]
4 mm × 4 mm, Very Very Thin Quad
(CP-24-7)
Dimensions shown in millimeters
ORDERING GUIDE
Model 1
AD8432ACPZ-R7
AD8432ACPZ-RL
AD8432ACPZ-WP
AD8432-EVALZ
1
Temperature Range
−40°C to +85°C
−40°C to +85°C
−40°C to +85°C
Package Description
24-Lead LFCSP_WQ, 7” Tape and Reel
24-Lead LFCSP_WQ, 13” Tape and Reel
24-Lead LFCSP_WQ, Waffle Pack
Evaluation Board
Z = RoHS Compliant Part.
©2009-2010 Analog Devices, Inc. All rights reserved. Trademarks and
registered trademarks are the property of their respective owners.
D08341-0-2/10(A)
Rev. A | Page 28 of 28
Package Option
CP-24-7
CP-24-7
CP-24-7