Quad Low Noise, Low Cost

Variable Gain Amplifier

AD8335

Rev. 0

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© 2004 Analog Devices, Inc. All rights reserved.

FEATURES

Low noise preamplifier (PrA)

Voltage noise = 1.3 nV/√Hz typical

Current noise = 2.4 pA/√Hz typical

Active input match

Input SNR (noise bandwidth = 20 MHz) = 92 dB

VGA

Differential output

Gain range (8 dB output gain step)

−10 dB to +38 dB—LO gain mode

−2 dB to +46 dB—HI gain mode

Accurate linear-in-dB gain control

PrA + VGA performance

−3 dB bandwidth of 70 MHz

Excellent overload performance

Supply: 5 V

Power consumption

95 mW/channel (380 mW total)

65 mW/channel (PrA off; 260 mW total)

Power-down

APPLICATIONS

Medical imaging (ultrasound, gamma cameras)

Sonar

Test and measurement

Precise, stable wideband gain control

FUNCTIONAL BLOCK DIAGRAM

63

PIP1

64

PMD1

1

PMD2

2

PIP2

4

PON2

5

POP2

6

VIP2

7

VIN2

10

VIN3

11

VIP3

12

POP3

13

PON3

15

PIP3

16

PMD3

17

PMD4

18

PIP4

61

60

59

58

53

55

52

51

49

47

VOH1

46

VOL1

56

VGN1

50

SL12

54

VGN2

43

VOL2

42

VOH2

39

VOH3

38

VOL3

27

VGN3

31

SL34

25

VGN4

35

VOL4

34

VOH4

20

21

22

23

28

26

29

30

32

18dB

18dB

18dB

18dB

VMD1

VMD2

VMD3

VMD4

INTERPOLATOR

INTERPOLATOR

INTERPOLATOR

INTERPOLATOR

20dB

TO

28dB

20dB

TO

28dB

20dB

TO

28dB

20dB

TO

28dB

ATTEN

–48dB TO

0dB

ATTEN

–48dB TO

0dB

ATTEN

–48dB TO

0dB

ATTEN

–48dB TO

0dB

GAIN INT

GAIN INT

GAIN INT

GAIN INT

AD8335

Figure 1.

GENERAL DESCRIPTION

The AD8335 is a quad variable gain amplifier (VGA) with low

noise preamplifier intended for cost and power sensitive

applications. Each channel features a gain range 48 dB, fully

differential signal paths, active input preamplifier matching, and

user-selectable maximum gains of 46 dB and 38 dB. Individual

gain controls are provided for each channel.

The preamplifier (PrA) has a single-ended to differential gain

of ×8 (18.06 dB) and accepts input signals ≤ 625 mV p-p. PrA

noise is 1.2 nV/√Hz and the combined input referred voltage

noise of the PrA and VGA is 1.3 nV/√Hz at maximum gain.

Assuming a 20 MHz noise bandwidth (NBW), the Nyquist

frequency for a 40 MHz ADC, the input SNR is 92 dB. The

HILO pin optimizes the output SNR for 10-bit and 12-bit

ADCs with 1 V p-p or 2 V p-p full-scale (FS) inputs.

Channels 1 and 2 are enabled through the EN12 pin while

Channels 3 and 4 are enabled through the EN34 pin. For VGA

only applications, the PrAs can be powered down, significantly

reducing power consumption.

The AD8335 is available in a 64-lead lead frame chip scale

(9 mm × 9 mm) package for the industrial temperature range

of −40°C to +85°C.