AD8334_15 Datasheet, PDF (1/56 Pages) Analog Devices – Ultralow Noise VGAs with Preamplifier and Programmable R

Ultralow Noise VGAs with
Preamplifier and Programmable R_IN
AD8331/AD8332/AD8334
FEATURES
Ultralow noise preamplifier (preamp)
Voltage noise = 0.74 nV/√Hz
Current noise = 2.5 pA/√Hz
3 dB bandwidth
AD8331: 120 MHz
AD8332, AD8334: 100 MHz
Low power
AD8331: 125 mW/channel
AD8332, AD8334: 145 mW/channel
Wide gain range with programmable postamp
−4.5 dB to +43.5 dB in LO gain mode
7.5 dB to 55.5 dB in HI gain mode
Low output-referred noise: 48 nV/√Hz typical
Active input impedance matching
Optimized for 10-bit/12-bit ADCs
Selectable output clamping level
Single 5 V supply operation
AD8332 and AD8334 available in lead frame chip scale package
APPLICATIONS
Ultrasound and sonar time-gain controls
High performance automatic gain control (AGC) systems
I/Q signal processing
High speed, dual ADC drivers
GENERAL DESCRIPTION
The AD8331/AD8332/AD8334 are single-, dual-, and quad-
channel, ultralow noise linear-in-dB, variable gain amplifiers
(VGAs). Optimized for ultrasound systems, they are usable as a
low noise variable gain element at frequencies up to 120 MHz.
Included in each channel are an ultralow noise preamp (LNA),
an X-AMP® VGA with 48 dB of gain range, and a selectable gain
postamp with adjustable output limiting. The LNA gain is 19 dB
with a single-ended input and differential outputs. Using a single
resistor, the LNA input impedance can be adjusted to match a
signal source without compromising noise performance.
The 48 dB gain range of the VGA makes these devices suitable
for a variety of applications. Excellent bandwidth uniformity is
maintained across the entire range. The gain control interface
provides precise linear-in-dB scaling of 50 dB/V for control
voltages between 40 mV and 1 V. Factory trim ensures excellent
part-to-part and channel-to-channel gain matching.
FUNCTIONAL BLOCK DIAGRAM
LON LOP VIP VIN
VCM
HILO
LNA
INH
19dB
V_MID 3.5dB OR 15.5dB
–
48dB
ATTENUATOR
21dB
PA
+
VOH
VOL
LMD
VCM
BIAS
VGA BIAS AND
INTERPOLATOR
GAIN
CONTROL
INTERFACE
CLAMP
AD8331/AD8332/AD8334
RCLMP
ENB GAIN
Figure 1. Signal Path Block Diagram
60
V_GAIN = 1V
50
V_GAIN = 0.8V
HI GAIN
MODE
40
V_GAIN = 0.6V
30
V_GAIN = 0.4V
20
V_GAIN = 0.2V
10
V_GAIN = 0V
0
–10
100k
1M
10M
100M
1G
FREQUENCY (Hz)
Figure 2. Frequency Response vs. Gain
Differential signal paths result in superb second- and third-
order distortion performance and low crosstalk.
The low output-referred noise of the VGA is advantageous in
driving high speed differential ADCs. The gain of the postamp
can be pin selected to 3.5 dB or 15.5 dB to optimize gain range
and output noise for 12-bit or 10-bit converter applications. The
output can be limited to a user-selected clamping level, preventing
input overload to a subsequent ADC. An external resistor adjusts
the clamping level.
The operating temperature range is −40°C to +85°C. The
AD8331 is available in a 20-lead QSOP package, the AD8332 is
available in 28-lead TSSOP and 32-lead LFCSP packages, and
the AD8334 is available in a 64-lead LFCSP package.
Rev. G
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