Quad VGA Provides 24-dB Gain Range for Communications, Medical Radiology, and Advanced Video Equipment

Space saving is a key design requirement for advanced systems in many applications. Next-generation 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 ADI’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, ADI’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 analogue 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.