Ultralow Power, Low Distortion,

Fully Differential ADC Drivers

Data Sheet

ADA4940-1/ADA4940-2

Rev. D

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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

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 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.

FUNCTIONAL BLOCK DIAGRAMS

NOTES

1. CONNECT THE EXPOSED PAD TO

DISABLE

–FB

+IN

–IN

+FB

–OUT

ADA4940-1

+OUT

12

11

10

1

3

4

9

2

Figure 1. ADA4940-1

–IN1

+FB1

–FB2

+IN2

DISABLE1

+OUT1

ADA4940-2

–OUT2

2

1

3

4

5

6

18

17

16

15

14

13

NOTES

1. CONNECT THE EXPOSED PAD TO

Figure 2. ADA4940-2

The ADA4940-1 is available in a 3 mm × 3 mm, 16-lead LFCSP

and an 8-lead SOIC. The ADA4940-2 is available in a 4 mm ×

4 mm, 24-lead LFCSP. The pinouts are 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 ADA4940-1/ADA4940-2

Product

(mA)

Bandwidth

(MHz)

Slew Rate

(V/μs)

Noise

(nV/√Hz)

AD8137

3

110

450

8.25

ADA4932-1

9

560

2800

3.6

ADA4941-1

2.2

31

22

5.1

Table 2. Complementary Products to ADA4940-1/ADA4940-2

Product

Power

(mW)

Throughput

(MSPS)

Resolution

(Bits)

SNR

(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