LF to 750 MHz
Digitally Controlled VGA

AD8370


Rev. 0
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However, no responsibility is assumed by Analog Devices for its use, nor for any
infringements of patents or other rights of third parties that may result from its use.
Specifications subject to change without notice. No license is granted by implication
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Tel: 781.329.4700 www.analog.com
Fax: 781.326.8703 © 2004 Analog Devices, Inc. All rights reserved.
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
VOCMPWUP
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
03692-
0-
001

Figure 1.
0
10
20
30
40
50
60
70
–30
–20
–10
0
10
20
30
40
VOLTAGE GAIN (
d
B)
VOLTAGE GAIN (
V
/V)
0 10203040 60 1050 70 80 90 110 120 130
GAIN CODE
03692-0-003
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.