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
AD7982
APPLICATIONS
OCM
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. 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
rightsof third parties that may result fromits 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 andregisteredtrademarks are the property of their respective owners.
One Technology Way, P.O. Box 9106, Norwood, MA 02062-9106, U.S.A.
Tel: 781.329.4700 www.analog.com
Fax: 781.461.3113 ©2011–2012 Analog Devices, Inc. All rights reserved.
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