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AD8488 128-Channel Digital X-Ray Analog Front End

The AD8488 is a 128-channel analog front end designed for use in high performance digital X-ray systems. The analog channels consist of an integrator followed by a gain selectable single-ended to low impedance differential output. The analog channel converts the charge acquired by X-ray or photodiode detectors to a voltage. The channels are composed of CMOS transistors, using typical high input impedance CMOS gates. The integrators generate charge dependent voltages using a range of selectable capacitance values that accommodate a broad range of input charge values. The integrators are followed by single-ended input to differential output voltage amplifiers where offset and low frequency noise voltages are subtracted from the input voltages. A 128:1 channel differential MUX follows the buffers and drives the analog output buffer. Switch drivers and certain digital timing functions are included, and all are mounted on a 255-lead BGA substrate. Charge conversion for all 128 channels is simultaneous followed by a sequential voltage output read of the channels using a 7-bit address code. The sequence occurs twice, sampling all 128 channels. Logic control inputs, CS_A and CS_B select the lower and upper 64-blocks of channel addresses.

The AD8488 is packaged in a 17 mm × 17 mm 255-lead RoHS compliant ball grid array (BGA). The operating temperature range is 0°C to 85°C ambient.

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