LF to 750 MHz,
Digitally Controlled VGA
AD8370
FUNCTIONAL BLOCK DIAGRAM
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
VCCI
VCCO VCCO
3
11
6
4
2
5
7
PWUP
ICOM
BIAS CELL
VOCM
OCOM
100 Ω differential output
1
8
OPHI
INHI
PRE
AMP
OUTPUT
AMP
TRANSCONDUCTANCE
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
9
16
15
INLO
ICOM
OPLO
OCOM
10
SHIFT REGISTER
AND LATCHES
AD8370
14
12
13
DATA CLCK LTCH
Figure 1.
Single 3 V to 5 V supply
70
40
CODE = LAST 7 BITS OF GAIN CODE
(NO MSB)
APPLICATIONS
60
50
40
30
20
10
0
30
20
10
0
Differential ADC drivers
IF sampling receivers
RF/IF gain stages
Cable and video applications
SAW filter interfacing
Single-ended-to-differential conversion
HIGH GAIN MODE
LOW GAIN MODE
HIGH GAIN MODE
Δ GAIN
≅ 0.409
≅ 0.059
Δ CODE
–10
–20
–30
GENERAL DESCRIPTION
Δ GAIN
Δ CODE
The AD8370 is a low cost, digitally controlled, variable gain
amplifier (VGA) 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.
LOW GAIN MODE
0
10 20 30 40 50 60 70 80 90 100 110 120 130
GAIN CODE
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.
For wide input, dynamic range applications, the AD8370
provides 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.
Fabricated on the ADI high speed XFCB process, the high
bandwidth 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.
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.
Rev. A
Information furnished by Analog Devices is believed to be accurate and reliable. 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 or otherwise under any patent or patent rights of Analog Devices.
Trademarks and registeredtrademarks arethe property of their respective owners.
One Technology Way, P.O. Box 9106, Norwood, MA 02062-9106, U.S.A.
Tel: 781.329.4700
Fax: 781.461.3113
www.analog.com
© 2005 Analog Devices, Inc. All rights reserved.
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