... The sensor portion of the chip consists of a 32x32 array of pixels on 26.4 m centers, with each pixel containing a 9.6 m x 13.2 m p-n diode detector, an amplifier and a multiplexer switch to the column bus. ... This would interfere with particle spectrometry, where the desired signal consists of a few events in an otherwise dark background. ... The primary performance parameter for an APS, whether used for charged particle spectrometry or for imaging, is the signal-to-noise ratio. ...