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 (3dB, 12dB, 18dB, 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 (7×7mm) or TQFP package.