Amplifier and Data Converter Selection Guide

34 Amplifiers
➔
Voltage-Controlled Gain Amplifiers
The voltage-controlled gain amplifier (VCA)
provides linear dB gain and gain-range
control with high impedance inputs. Available
in single, dual and octal configurations, the
VCA series is designed to be used as a flexible
gain-control element in a variety of electronic
systems. With a broad gain-control range,
both gain and attenuation control are provided
for maximum flexibility.
Technical Information
The broad attenuation range can be used for
gradual or controlled channel turn-on or turnoff
where abrupt gain changes can create
artifacts and other errors.
V CNTL A
V CLMP A
Typical Applications
• Ultrasound systems
• Medical and industrial
• Test equipment
Gain C EXT A
Select A
Design Considerations
Primary
• Input frequency
• Noise (nV/ Hz)
• Variable gain range
In A+
In A– -
Clamping
V- I Circuitry
I- V
Out A+
Out A–
Secondary
• Number of channels
• Distortion—low second harmonic and third
harmonic distortion
• Level of integration
• Per channel power consumption
In B+
In B –
Clamping
V- I Circuitry
I- V
V CNTL B
V CLMP B
Gain
Select B
C EXT B
Out B+
Out B–
VCA2617 functional block diagram.
Two-Channel Variable Gain Amplifier
VCA2615
Get samples, datasheets, EVMs and app reports at: www.ti.com/sc/device/VCA2615
Key Features
• Ultra-low noise LNP: 0.7nV/ Hz
• Programmable LNP gains
• Buffered LNP outputs for CW
• VGA gain control range: 52dB
• Linear control response: 22dB/V
• Adjustable output clipping
• Bandwidth: 42MHz
• Single supply: 5V
• Packaging: Small QFN-48 (7x7)
The VCA2615 is a two-channel variable gain amplifier well suited to high-end ultrasound
systems. Excellent performance enables use in high-performance applications. Each channel consists
of a programmable low noise preamplifier (LNP) and a variable gain amplifier (VGA).
LNP IN +
LNP IN –
FB1 FB2 FB3 FB4
Feedback
Resistors
LNP
LNP OUT –
+1
LNP OUT + VCA IN + VCA IN – H/L
+1
MUX
VGA
(0dB or
+6dB)
VCA OUT +
VCA OUT –
(3, 12, 18, 22dB)
1/2 VCA2615
VCA2615
52dB
Range
VCA2615 functional block diagram.
G1 G2 VCA IN SEL V CNTL V CLMP
Amplifier and Data Converter Selection Guide Texas Instruments 3Q 2006