LF to 750 MHz

Digitally Controlled VGA

AD8370

Rev. 0

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FEATURES

Programmable low and high gain (<2 dB resolution)

Low range: −11 dB to +17 dB

High range: +6 dB to +34 dB

Differential input and output:

200 Ω differential input

100 Ω differential output

7 dB noise figure @ maximum gain

Two-tone IP3 of +35 dBm @ 70 MHz

−3 dB bandwidth of 750 MHz

40 dB precision gain range

Serial 8-bit digital interface

Wide input dynamic range

Power-down feature

Single 3 V to 5 V supply

APPLICATIONS

Differential ADC drivers

IF sampling receivers

RF/IF gain stages

Cable and video applications

SAW filter interfacing

Single-ended-to-differential conversion

GENERAL DESCRIPTION

The AD8370 is a low cost, digitally controlled, variable gain

amplifier that provides precision gain control, high IP3, and low

noise figure. The excellent distortion performance and wide

bandwidth make the AD8370 a suitable gain control device for

modern receiver designs.

For wide input, dynamic range applications, the AD8370 pro-

vides two input ranges: high gain mode and low gain mode. A

vernier 7-bit transconductance (Gm) stage provides 28 dB of

gain range at better than 2 dB resolution, and 22 dB of gain

range at better than 1 dB resolution. A second gain range, 17 dB

higher than the first, can be selected to provide improved noise

performance.

The AD8370 is powered on by applying the appropriate logic

level to the PWUP pin. When powered down, the AD8370

consumes less than 4 mA and offers excellent input to output

isolation. The gain setting is preserved when operating in a

power-down mode.

FUNCTIONAL BLOCK DIAGRAM

INHI

INLO

OPHI

OPLO

VCCO

OCOM

ICOM

VOCM

PWUP

VCCO

OCOM

VCCI

ICOM

BIAS CELL

SHIFT REGISTER

AND LATCHES

PRE

AMP

TRANSCONDUCTANCE

OUTPUT

AMP

11

6

1

16

4

14

13

12

5

9

8

3

2

10

7

15

DATA CLCK LTCH

AD8370

Figure 1.

0

10

20

30

40

50

60

70

–30

–20

–10

0

10

20

30

40

0

1020

3040

60

100

50

70

80

90

110 120 130

GAIN CODE

CODE = LAST 7 BITS OF GAIN CODE

(NO MSB)

HIGH GAIN MODE

HIGH GAIN MODE

LOW GAIN MODE

LOW GAIN MODE

∆ GAIN

∆ CODE

≅ 0.409

∆ GAIN

∆ CODE

≅ 0.059

Figure 2. Gain vs. Gain Code at 70 MHz

Gain control of the AD8370 is through a serial 8-bit gain control

word. The MSB selects between the two gain ranges, and the

remaining 7 bits adjust the overall gain in precise linear gain steps.

Fabricated on the ADI high speed XFCB process, the high band-

width of the AD8370 provides high frequency and low distortion.

The quiescent current of the AD8370 is 78 mA typically. The

AD8370 amplifier comes in a compact, thermally enhanced

16-lead TSSOP package and operates over the temperature

range of −40°C to +85°C.