Ultralow Power, Low Distortion
Fully Differential ADC Driver
Data Sheet
ADA4940-1/ADA4940-2
FEATURES
FUNCTIONAL BLOCK DIAGRAMS
Small signal bandwidth: 260 MHz
Ultralow power 1.25mA
Extremely low harmonic distortion
−122 dB THD at 50 kHz
−96 dB THD at 1 MHz
Low input voltage noise: 3.9 nV/√Hz
0.35 mV maximum offset voltage
Balanced outputs
ADA4940-1
–IN1 1
+FB1 2
18 +OUT1
17 V
12 DISABLE
11 –OUT
–FB
1
OCM1
16 –V
+IN 2
–IN 3
+V
+V
3
4
S2
S2
S1
ADA4940-2
–V
15
14
S1
10 +OUT
–FB2 5
+IN2 6
DISABLE2
+FB
4
9 V
OCM
13 –OUT2
Settling time to 0.1%: 34 ns
Rail-to-rail output: −VS + 0.1 V to +VS − 0.1 V
Adjustable output common-mode voltage
Flexible power supplies: 3 V to 7 V (LFCSP)
Disable pin to reduce power consumption
ADA4940-1 is available in LFCSP and SOIC packages
Figure 1.
0
C
F
+D
IN
2.5V
IN+ REF VDD
–20
–40
–60
–80
R3
R4
+
33Ω
+IN
–OUT
2.7nF
2.7nF
V
OCM
AD7982
APPLICATIONS
ADA4940-1
+OUT
33Ω
IN–
GND
–IN
Low power PulSAR®/SAR ADC drivers
Single-ended-to-differential conversion
Differential buffers
–
R1
R2
–D
IN
C
F
–100
–120
–140
–160
Line drivers
Medical imaging
Industrial process controls
Portable electronics
GENERAL DESCRIPTION
0
20k
40k
60k
80k
100k
FREQUENCY (Hz)
The ADA4940-1/ADA4940-2 are low noise, low distortion fully
differential amplifiers with very low power consumption. They
are an ideal choice for driving low power, high resolution, high
performance SAR and sigma-delta (Σ-Δ) analog-to-digital
converters (ADCs) with resolutions up to 16 bits from dc to
1 MHz on only 1.25 mA of quiescent current. The adjustable
level of the output common-mode voltage allows the ADA4940-1/
ADA4940-2 to match the input common-mode voltage of
multiple ADCs. The internal common-mode feedback loop
provides exceptional output balance, as well as suppression of
even-order harmonic distortion products.
Figure 2. ADA4940-1 Driving the AD7982 ADC
The ADA4940-1 is available in a Pb-free, 3 mm × 3 mm, 16-lead
LFCSP, and an 8-lead SOIC. The ADA4940-2 is available in a Pb-
free, 4 mm × 4 mm, 24-lead LFCSP. The pinout is optimized to
facilitate printed circuit board (PCB) layout and minimize
distortion. The ADA4940-1/ADA4940-2 are specified to
operate over the −40°C to +125°C temperature range.
Table 1. Similar Products to the ADA4940-1/ADA4940-2
Isupply
(mA)
Bandwidth
(MHz)
Slew Rate
(V/µs)
Noise
(nV/√Hz)
Product
AD8137
ADA4932-x
ADA4941-1
3
9
2.2
110
560
31
450
2800
22
8.25
3.6
5.1
With the ADA4940-1/ADA4940-2, differential gain
configurations are easily realized with a simple external feedback
network of four resistors determining the closed-loop gain of
the amplifier. The ADA4940-1/ADA4940-2 are fabricated using
Analog Devices, Inc., SiGe complementary bipolar process,
enabling them to achieve very low levels of distortion with an
input voltage noise of only 3.9 nV/√Hz. The low dc offset and
excellent dynamic performance of the ADA4940-1/ADA4940-2
make them well suited for a variety of data acquisition and signal
processing applications.
Table 2. Complementary Products to the ADA4940-1/ADA4940-2
Power
(mW)
Throughput
(MSPS)
Resolution
(Bits)
SNR
(dB)
Product
AD7982
AD7984
AD7621
AD7623
7.0
10.5
65
1
18
18
16
16
98
96.5
88
1.333
3
1.333
45
88
Rev. C
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Trademarks andregisteredtrademarks are the property of their respective owners.
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Tel: 781.329.4700 ©2011–2013 Analog Devices, Inc. All rights reserved.
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