LF to 750 MHz
Digitally Controlled VGA
AD8370
FUNCTIONAL BLOCK DIAGRAM
FEATURES
VCCI
3
VCCO VCCO
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
11
6
4
2
5
7
PWUP
ICOM
BIAS CELL
VOCM
OCOM
1
8
OPHI
INHI
100 Ω differential output
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
9
16
INLO
OPLO
OCOM
ICOM 15
10
SHIFT REGISTER
AND LATCHES
Serial 8-bit digital interface
Wide input dynamic range
AD8370
14
12
13
Power-down feature
DATA CLCK LTCH
Single 3 V to 5 V supply
Figure 1.
APPLICATIONS
Differential ADC drivers
IF sampling receivers
RF/IF gain stages
Cable and video applications
SAW filter interfacing
70
60
50
40
30
20
10
0
40
30
20
10
0
CODE = LAST 7 BITS OF GAIN CODE
(NO MSB)
HIGH GAIN MODE
LOW GAIN MODE
HIGH GAIN MODE
∆ GAIN
≅ 0.409
Single-ended-to-differential conversion
∆ CODE
GENERAL DESCRIPTION
–10
–20
–30
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.
∆ GAIN
∆ CODE
≅ 0.059
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
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.
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.
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. 0
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
registered trademarks are the property of their respective owners.
One Technology Way, P.O. Box 9106, Norwood, MA 02062-9106, U.S.A.
Tel: 781.329.4700
Fax: 781.326.8703
www.analog.com
© 2004 Analog Devices, Inc. All rights reserved.
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