ADA4940-1 Datasheet, PDF (1/32 Pages) Analog Devices – Ultralow Power, Low Distortion

Data Sheet
FEATURES
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
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
APPLICATIONS
Low power PulSAR®/SAR ADC drivers
Single-ended-to-differential conversion
Differential buffers
Line drivers
Medical imaging
Industrial process controls
Portable electronics
GENERAL DESCRIPTION
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.
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.
Rev. B
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Ultralow Power, Low Distortion
Fully Differential ADC Driver
ADA4940-1/ADA4940-2
FUNCTIONAL BLOCK DIAGRAMS
–FB 1
+IN 2
–IN 3
+FB 4
ADA4940-1
12 DISABLE
11 –OUT
10 +OUT
9 V_OCM
–IN1 1
+FB1 2
+V_S1 3
+V_S1 4
–FB2 5
+IN2 6
ADA4940-2
18 +OUT1
17 V_OCM1
16 –V_S2
15 –VS2
14 DISABLE2
13 –OUT2
0
–20
–40
–60
–80
–100
Figure 1.
C_F
+D_IN
R3
R4
+IN ⁺
33Ω
VOCM
–OUT
ADA4940-1
+OUT
2.7nF
2.7nF
–IN _–
33Ω
R1
R2
–D_IN
C_F
2.5V
IN+ REF VDD
AD7982
IN– _GND
–120
–140
–160
0
20k
40k
60k
80k
100k
FREQUENCY (Hz)
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
Product
Isupply Bandwidth Slew Rate Noise
(mA)
(MHz)
(V/µs)
(nV/√Hz)
AD8137
3
110
450
8.25
ADA4932-x 9
560
2800
3.6
ADA4941-1 2.2
31
22
5.1
Table 2. Complementary Products to the ADA4940-1/ADA4940-2
Product
Power Throughput Resolution SNR
(mW) (MSPS)
(Bits)
(dB)
AD7982
7.0
1
18
98
AD7984
10.5
1.333
18
96.5
AD7621
65
3
16
88
AD7623
45
1.333
16
88
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