ANALOG DEVICES AD8264 Service Manual

Quad, 235 MHz, DC-Coupled VGA

AD8264

VOCM

VPOS

IPP1

GNH1

IPN1

ATTENUATOR
–24dB TO 0d B

VOH1

VOL1

IPP3

GNH3

IPN3

VOH3

VOL3

6dB

IPP4

GNH4

IPN4

+
–

PrA
6dB

+
–

PrA
6dB

+
–

PrA
6dB

+
–

PrA
6dB

VOH4

VOL4

6dB

IPP2

GNH2

IPN2

ATTENUATOR
–24dB TO 0d B

ATTENUATOR
–24dB TO 0d B

ATTENUATOR
–24dB TO 0d B

VOH2

VOL2

OPP2

GNLO

OPP3

OPP4

18dB

18dB

18dB

18dB

OFS2

OFS1

OFS3

OFS4

VNEG

VGA1

VGA2

VGA3

COMM

OPP1

VGA4

+
–

+
–

+
–

+
–

CH1 GAIN
CONTROL

CH2 GAIN
CONTROL

CH3 GAIN

CONTROL

CH4 GAIN
CONTROL

6dB

6dB

07736-001

FEATURES

Low noise

Voltage noise: 2.3 nV/√Hz
Current noise: 2 pA/√Hz

Wide bandwidth

Small signal: 235 MHz (VGAx); 80 MHz (differential 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 @ ±3.3 V

APPLICATIONS

Multichannel data acquisition
Positron emission tomography
Gain trim
Industrial and medical ultrasound
Radar receivers

and Differential Output Amplifier

FUNCTIONAL BLOCK DIAGRAM

GENERAL DESCRIPTION

The AD8264 is a 4-channel, linear-in-dB, general-purpose
variable gain amplifier (VGA) with a preamplifier (preamp),
and a flexible differential output buffer. Intended for a broad
range of applications, 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 low­distortion 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.

Rev. A

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rights of third parties that may result from its use. Specifications subject to change without notice. No
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Figure 1.

The gain of each channel is adjusted independently, and all
channels are referenced to a single pin, GNLO. Combined with
a multi-output, digital-to-analog converter (DAC), each section
of the AD8264 can be used for active calibration or as a trim
amplifier.

The gain range of the VGA section is 24 dB. Operation from
a dual polarity power supply enables amplification of negative
voltage pulses that are generated by current-sinking pulses into
a grounded load, such as is typical of photodiodes or photo­multiplier tubes (PMT). Delay-free processing of wide-band
video signals is also possible. The differential output amplifier
permits convenient level shifting and interfacing to single­supply ADCs using the VOCM and OFSx pins.

The AD8264 is available in a 40-lead, 6 mm × 6 mm LFCSP
with an operating temperature range of −40°C to +105°C.

One Technology Way, P.O. Box 9106, Norwood, MA 02062-9106, U.S.A.
Tel: [phone]
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