VCA2615 Datasheet, PDF (1/29 Pages) Texas Instruments – Dual, Low-Noise Variable-Gain Amplifier with Preamp

VCA2615
SBOS316C − JULY 2005 − REVISED SEPTEMBER 2005
Dual, Low-Noise
Variable-Gain Amplifier with Preamp
FEATURES
D VERY LOW NOISE: 0.7nV//Hz
D LOW-NOISE PREAMP (LNP)
− Active Termination
− Programmable Gains: 3, 12, 18, 22dB
− Programmable Input Impedance (R_F)
− Buffered, Differential Outputs for CW
Processing
− Excellent Input Signal Handling
Capabilities
D LOW-NOISE VARIABLE-GAIN AMPLIFIER
− High/Low-Mode (0/+6dB)
− 52dB Gain Control Range
− Linear Control Response: 22dB/V
− Switchable Differential Inputs
− Adjustable Output Clipping-Level
D BANDWIDTH: 42MHz
D HARMONIC DISTORTION: −55dB
D 5V SINGLE SUPPLY
D LOW-POWER: 154mW/Channel
D POWER-DOWN MODES
D SMALL QFN-48 PACKAGE (7x7mm)
APPLICATIONS
D MEDICAL AND INDUSTRIAL ULTRASOUND
SYSTEMS
− Suitable for 10-Bit and 12-Bit Systems
D TEST EQUIPMENT
DESCRIPTION
The VCA2615 is a dual-channel, variable gain amplifier
consisting of a Low-Noise Preamplifier (LNP) and a Variable-
Gain Amplifier (VGA). This combination along with the device
features makes it well-suited for a variety of ultrasound
systems.
The LNP offers a high level of flexibility to adapt to a wide range
of systems and probes. The LNP gain can be programmed to
one of four settings (3, 12, 18, 22dB), while maintaining
excellent noise and signal handling characteristics. The input
impedance of the LNP can be controlled by selecting one of
the built-in feedback resistors.This active termination allows
the user to closely match the LNP to a given source
impedance, resulting in optimized overall system noise
performance. The differential LNP outputs are provided either
as buffered outputs for further CW processing, or fed directly
into the variable-gain amplifier (VGA). Alternatively, an
external signal can be applied to the differential VGA inputs
through a programmable switch.
Following a linear-in-dB response, the gain of the VGA can be
varied over a 52dB range with a 0.2V to 2.5V control voltage
common to both channels of the VCA2615. In addition, the
overall gain can be switched between a 0dB and +6dB
postgain, allowing the user to optimize the output swing of
VCA2615 for a variety of high-speed Analog-to-Digital
Converters (ADCs). As a means to improve system overload
recovery time, the VCA2615 provides an internal clipping
function where an externally applied voltage sets the desired
clipping level.
The VCA2615 operates on a single +5V supply and is
available in a small QFN-48 package (7x7mm).
FB1 FB2 FB3 FB4 LNP_OUT− LNP_OUT+ VCA_IN+ VCA_IN−
Feedback
Resistors
+1
+1
H/L
(0dB or
+6dB)
LNP_IN+
LNP_IN−
LNP
(3, 12, 18, 22dB)
1/2 VCA2615
G1 G1
MUX
VGA
52dB
Range
VCA_INSEL
V_CNTL V_CLMP
VCA_OUT+
VCA_OUT−
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PRODUCTION DATA information is current as of publication date. Products
conform to specifications per the terms of Texas Instruments standard warranty.
Production processing does not necessarily include testing of all parameters.
Copyright  2005, Texas Instruments Incorporated
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