41 dB Range, 1 dB Step Size,

Programmable Dual VGA

AD8372

Rev. 0

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FEATURES

Dual independent digitally controlled VGA

Differential input and output

150 Ω differential input

Open-collector differential output

7.8 dB noise figure to 100 MHz @ maximum gain

HD2/HD3 better than 77 dBc for 1 V p-p differential output

−3 dB bandwidth of 150 MHz

41 dB gain range

1 dB step size ± 0.2 dB

Serial 8-bit bidirectional SPI control interface

Wide input dynamic range

Pin-programmable output stage

Power-down feature

Single 5 V supply: 106 mA per channel

32-lead LFCSP, 5 mm × 5 mm package

APPLICATIONS

Differential ADC drivers

CMTS upstream direct sampling receivers

CATV modem signal scaling

Generic RF/IF gain stages

Single-ended-to-differential conversion

FUNCTIONAL BLOCK DIAGRAM

ENB1

IPC1

INC1

CLK1

RXT2

LCH1

IPC2

INC2

REF1

SDI1

SDO1

REF2

OPC1

ONC1

RXT2

SDI2

LCH2

OPC2

ENB2

ONC2

SDO2

CLK2

POSTAMP

CHANNEL 1

POSTAMP

CHANNEL 2

REGISTERS

AND

GAIN DECODER

AD8372

Figure 1.

GENERAL DESCRIPTION

The AD8372 is a dual, digitally controlled, variable gain

amplifier that provides precise gain control, high IP3, and

low noise figure. The excellent distortion performance and

moderate signal bandwidth make the AD8372 a suitable

gain control device for a variety of multichannel receiver

applications.

For wide input dynamic range applications, the AD8372

provides a broad 41 dB gain range. The gain is programmed

through a bidirectional 4-pin serial interface. The serial inter-

face consists of a clock, latch, data input, and data output lines

for each channel.

The AD8372 provides the ability to set the transconductance of

the output stage using a single external resistor. The RXT1 and

RXT2 pins provide a band gap derived stable reference voltage

of 1.56 V. Typically 2.0 kΩ shunt resistors to ground are used to

set the maximum gain to a nominal value of 31 dB. The current

setting resistors can be adjusted to manipulate the gain and

distortion performance of each channel. This is a flexible

feature in applications where it is desirable to trade off distortion

performance for lower power consumption.

The AD8372 is powered on by applying the appropriate logic

level to the ENB1, ENB2 pins. When powered down, the AD8372

consumes less than 2.6 mA and offers excellent input-to-output

isolation. The gain setting is preserved when powered down.

Fabricated on an Analog Devices high frequency BiCMOS

process, the AD8372 provides precise gain adjustment capabilities

with good distortion performance. The quiescent current of the

AD8372 is typically 106 mA per channel. The AD8372 amplifier

comes in a compact, thermally enhanced 5 mm × 5 mm 32-lead

LFCSP package and operates over the temperature range of

−40°C to +85°C.