
Ultralow Distortion
Differential ADC Driver
ADA4939-1/ADA4939-2
Rev. 0
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FEATURES
Extremely low harmonic distortion
102 dBc HD2 @ 10 MHz
83 dBc HD2 @ 70 MHz
77 dBc HD2 @ 100 MHz
101 dBc HD3 @ 10 MHz
97 dBc HD3 @ 70 MHz
91 dBc HD3 @ 100 MHz
Low input voltage noise: 2.3 nV/√Hz
High speed
3 dB bandwidth of 1.4 GHz, G = 2
Slew rate: 6800 V/μs, 25% to 75%
Fast overdrive recovery of <1 ns
±0.5 mV typical offset voltage
Externally adjustable gain
Stable for differential gains ≥2
Differential-to-differential or single-ended-to-differential
operation
Adjustable output common-mode voltage
Single-supply operation: 3.3 V to 5 V
APPLICATIONS
ADC drivers
Single-ended-to-differential converters
IF and baseband gain blocks
Differential buffers
Line drivers
GENERAL DESCRIPTION
The ADA4939 is a low noise, ultralow distortion, high speed
differential amplifier. It is an ideal choice for driving high
performance ADCs with resolutions up to 16 bits from dc to
100 MHz. The output common-mode voltage is user adjustable
by means of an internal common-mode feedback loop, allowing
the ADA4939 output to match the input of the ADC. The internal
feedback loop also provides exceptional output balance as well as
suppression of even-order harmonic distortion products.
With the ADA4939, differential gain configurations are easily
realized with a simple external feedback network of four resistors
that determine the closed-loop gain of the amplifier.
The ADA4939 is fabricated using Analog Devices, Inc., proprietary
silicon-germanium (SiGe), complementary bipolar process,
enabling it to achieve very low levels of distortion with an input
voltage noise of only 2.3 nV/√Hz. The low dc offset and excellent
dynamic performance of the ADA4939 make it well suited for a
wide variety of data acquisition and signal processing applications.
FUNCTIONAL BLOCK DIAGRAMS
1
–FB
2
+IN
3
–IN
4
+FB
11 –OUT
12 PD
10 +OUT
9VOCM
5
+
V
S
6
+
V
S
7
+
V
S
8
+
V
S
15
–V
S
16
–V
S
14
–V
S
13
–V
S
ADA4939-1
074
29
-00
1
Figure 1. ADA4939-1
ADA4939-2
1
–IN1
2
+FB1
3
+VS1
4
+VS1
5
–FB2
6
+IN2
15 –VS2
16 –VS2
17 VOCM1
18 +OUT1
14 PD2
13 –OUT2
7
–I
N
2
8
+
F
B
2
9
+
V
S
2
11
V
O
C
M
2
12
+
O
U
T
2
10
+
V
S
2
21
–V
S
1
22
–V
S
1
23
–
F
B
1
24
+
IN
1
20
P
D
1
19
–O
U
T
1
07
42
9-
0
02
Figure 2. ADA4939-2
–60
–110
–105
–100
–95
–90
–85
–80
–75
–70
–65
1
10
100
HAR
M
O
NI
C
DI
S
T
O
RT
IO
N
(
d
Bc)
FREQUENCY (MHz)
HD2
HD3
VOUT, dm = 2V p-p
07
42
9-
0
21
Figure 3. Harmonic Distortion vs. Frequency
The ADA4939 is available in a Pb-free, 3 mm × 3 mm 16-lead
LFCSP (ADA4939-1, single) or a Pb-free, 4 mm × 4 mm 24-lead
LFCSP (ADA4939-2, dual). The pinout has been optimized to
facilitate PCB layout and minimize distortion. The ADA4939-1
and the ADA4939-2 are specified to operate over the 40°C to
+105°C temperature range; both operate on supplies between
3.3 V and 5 V.