FEATURES
128 integrator channels
Correlated double sample error correction (CDS)
Corrects for VOS and LF noise
Power consumption per channel
Normal: 11 mW
Low power: 4 mW
Low input leakage current: −1.5 pA typical
Low input referred noise (QNI): 993 e−rms typical
Linearity error: 0.03% typical
Compact 17 mm × 17 mm BGA
Selectable filter time constants
4 selectable input charge ranges
10 selectable gain ranges

APPLICATION
High performance digital X-ray systems
Medical X-ray
Security (baggage scanner) systems

GENERAL DESCRIPTION
The AD8488 is a 128-channel, analog front end (AFE) 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 the channel
addresses.
The AD8488 is packaged in a 17 mm × 17 mm, 255-lead, RoHScompliant
ball grid array (BGA). The operating temperature range
is 0°C to 85°C ambient.