Ultralow Power, Low Distortion

Fully Differential ADC Driver

Data Sheet

ADA4940-1/ADA4940-2

Rev. B

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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 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.

FUNCTIONAL BLOCK DIAGRAMS

1

–FB

2

+IN

3

–IN

4

+FB

11 –OUT

12 DISABLE

10 +OUT

9

ADA4940-1

ADA4940-2

1

–IN1

2

+FB1

3

4

5

–FB2

6

+IN2

18 +OUT1

14 DISABLE2

13 –OUT2

Figure 1.

0

–160

–140

–120

–100

–80

–60

–40

–20

0

20k

40k

60k

80k

100k

FREQUENCY (Hz)

R1

R2

R4

R3

+IN

–OUT

33Ω

2.5V

AD7982

ADA4940-1

33Ω

2.7nF

2.7nF

+OUT

+

–

–IN

IN+

IN– GND

VDD

REF

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

(mA)

Bandwidth

(MHz)

Slew Rate

(V/µs)

Noise

(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

(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