Document
Data Sheet
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 (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.
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.
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.
LF to 750 MHz, Digitally Controlled VGA
AD8370
FUNCTIONAL BLOCK DIAGRAM
VCCI 3
VCCO VCCO 11 6
PWUP 4 ICOM 2
INHI 1
INLO 16
PRE AMP
BIAS CELL
TRANSCONDUCTANCE
OUTPUT AMP
5 VOCM 7 OCOM 8 OPHI
9 OPLO
ICOM 15
SHIFT REGISTER AND LATCHES
14 13 12 DATA CLCK LTCH
Figure 1.
10 OCOM
AD8370
03692-001
70 CODE = LAST 7 BITS OF GAIN CODE (NO MSB)
60 HIGH GAIN MODE
50
LOW GAIN MODE 40
HIGH GAIN MODE 30
40
30
20
GAIN 0.409 CODE
10 0
VOLTAGE GAIN (dB)
VOLTAGE GAIN (V/V)
03692-002
20 –10
10
LOW GAIN MODE
GAIN 0.059 CODE
–20
0 –30 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.
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.
Rev. B
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AD8370
TABLE OF CONTENTS
Features .............................................................................................. 1
Applications....................................................................................... 1
General Description ......................................................................... 1
Functional Block Diagram .............................................................. 1
Revision History ............................................................................... 2
Specifications..................................................................................... 3
Absolute Maximum Ratings............................................................ 5
ESD Caution.................................................................................. 5
Pin Configuration and Function Descriptions............................. 6
Typical Performance Characteristics ............................................. 7
Theory of Operation ...................................................................... 13
Block Architecture...................................................................... 13
Preamplifier................................................................................. 13
Transconductance Stage ............................................................ 13
Output Amplifier........................................................................ 14
Digital Interface and Timing .................................................... 14
Applications..................................................................................... 15
REVISION HISTORY
12/11—Rev. A t.