Quad, 235 MHz, DC-Coupled VGA

and Differential Output Amplifier

Data Sheet

AD8264

Rev. B

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FEATURES

Low noise

Voltage noise: 2.3 nV/√Hz

Current noise: 2 pA/√Hz

Wide bandwidth

Small signal: 235 MHz (VGAx); 80 MHz (output amplifier)

Large signal: 80 MHz (1 V p-p)

Gain range

0 to 24 dB (input to VGA output)

6 to 30 dB (input to differential output)

Gain scaling: 20 dB/V

DC-coupled

Single-ended input and differential output

Supplies: ±2.5 V to ±5 V

Low power: 140 mW per channel at ±3.3 V

APPLICATIONS

Multichannel data acquisition

Positron emission tomography

Gain trim

Industrial and medical ultrasound

Radar receivers

GENERAL DESCRIPTION

The AD8264 is a quad, linear-in-dB, general-purpose variable

gain amplifier (VGA) with a preamplifier (preamp), and a flexible

differential output buffer. DC coupling, combined with wide

bandwidth, makes this amplifier a very good pulse processor.

Each channel includes a single-ended input preamp/VGA section

to preserve the wide bandwidth and fast slew rate for low dis-

tortion pulse applications. A 6 dB differential output buffer with

common-mode and offset adjustments enable direct coupling to

most modern high speed analog-to-digital converters (ADCs),

using the converter reference output for perfect dc matching levels.

The −3 dB bandwidth of the preamp/VGA is dc to 235 MHz,

and the bandwidth of the differential driver is 80 MHz. The

floating gain control interface provides a precise linear-in-dB scale

of 20 dB/V and is easy to interface to a variety of external circuits.

The gain of each channel is adjusted independently, and all

channels are referenced to a single pin, GNLO. Combined with

a multioutput, digital-to-analog converter (DAC), each section

of the AD8264 can be used for active calibration or as a trim

amplifier.

Operation from a bipolar power supply enables amplification of

negative voltage pulses generated by current-sinking pulses into

a grounded load, such as is typical of photodiodes or photo-

multiplier tubes (PMT). Delay-free processing of wideband

video signals is also possible.

FUNCTIONAL BLOCK DIAGRAM

IPPx

VPOS

IPNx

VOLx

VOHx

INTERPOLATOR

PREAMP

6dB (2×)

OFSx

OPPx

GAIN

INTERFACE

100Ω

747Ω

107Ω

100Ω

+

–

VOCM

COMM

GNHx

GNLO

BIAS

VNEG

VGAx

ONE CHANNEL SHOWN

ATTENUATOR

–24dB TO 0dB

FIXEDGAINVGA

AMPLIFIER

18dB (8×)

DIFFERENTIAL OUTPUT

AMPLIFIER 6dB (2×)

1kΩ

2kΩ

1kΩ

2kΩ

Figure 1.