Quad, 235 MHz, DC-Coupled VGA
and Differential Output Amplifier
AD8264
FUNCTIONAL BLOCK DIAGRAM
FEATURES
COMM
VPOS
VNEG
Low noise
OPP1
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
VGA1
VOL1
+
IPP1
IPN1
PrA
6dB
ATTENUATOR
–24dB TO 0dB
+
18dB
6dB
–
–
VOH1
OFS1
GNH1
+
CH1 GAIN
CONTROL
–
OPP2
IPP2
IPN2
VGA2
VOL2
+
PrA
6dB
ATTENUATOR
–24dB TO 0dB
+
18dB
18dB
18dB
6dB
–
–
VOH2
OFS2
GNH2
+
CH2 GAIN
CONTROL
–
OPP3
IPP3
IPN3
VGA3
VOL3
+
PrA
6dB
ATTENUATOR
–24dB TO 0dB
+
6dB
Low power: 140 mW per channel @ 3.3 V
–
–
VOH3
OFS3
GNH3
+
CH3 GAIN
CONTROL
–
APPLICATIONS
OPP4
IPP4
VGA4
VOL4
Multichannel data acquisition
Positron emission tomography
Gain trim
Industrial and medical ultrasound
Radar receivers
+
ATTENUATOR
–24dB TO 0dB
PrA
6dB
+
6dB
–
IPN4
–
VOH4
OFS4
GNH4
+
CH4 GAIN
CONTROL
–
VOCM
GNLO
Figure 1.
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 band-
width makes this amplifier a very good pulse processor.
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.
Each channel includes a single-ended input preamp/VGA
section to preserve the wide bandwidth and fast slew rate for low-
distortion 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 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 photo-
multiplier tubes (PMT). Delay-free processing of wide-band
video signals is also possible. The differential output amplifier
permits convenient level shifting and interfacing to single-
supply ADCs using the VOCM and OFSx pins.
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 AD8264 is available in a 40-lead, 6 mm × 6 mm LFCSP
with an operating temperature range of −40°C to +105°C.
Rev. 0
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