The AD8264 is the new four-channel VGA and the first to integrate four analog-to-digital converter (ADC) drivers, enabling radiological equipment designers, for example, to reduce printed-circuit board area and simplify layout by replacing eight components with a single device.
New PET scanner designs are increasing channel densities to enhance image resolution and improve patient diagnostics, despite limits to the physical size of the scanning element, or gantry. The high-speed AD8264 VGA has a single-ended output for wide-bandwidth applications, and auxiliary differential ADC drivers that operate with the company’s data converters, including the AD9222 octal and AD9228 quad 12-bit ADCs.
The AD8264 quad VGA is also suited for wireless infrastructure equipment where its four DC-coupled channels and precise gain control allow communication-systems designers to more easily adjust output-signal levels and eliminate the time and cost associated with matching four discrete VGAs. For advanced broadcast and video-security applications, the company’s new VGA improves picture quality by more accurately white-balancing RGB (red-green-blue) signals and better managing gain-trim calibration over the system’s life.
Each of the AD8264’s four linear-in-dB VGA channels has independent gain control. Each channel comprises a high-impedance preamplifier, a high-speed VGA, and a differential output amplifier. The AD8264’s pinout provides single-ended output taps directly from the VGAs, which have a -3 dB bandwidth of 235 MHz, and balanced outputs from the 80-MHz output amplifiers. Dual supply operation enables gain control of negative-going pulses such as those that photodiodes, photo-multiplier tubes, and video signal-sources generate. With a 24-dB gain range, the AD8264 features a gain-control interface that provides a precise 20 dB/V linear-in-dB scale. A common gain-control reference for all channels simplifies wiring. The differential gain-control structure accommodates a wide range of common-mode operating points, simplifying the interface to any analog or digital control source. A VOCM pin sets the common-mode voltage of the differential output stage to match most modern single-supply ADCs, and allows for dc level-shift of the output. Power consumption is 125-mW per channel at ±3.3V.
