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AD8488 and charge amplifiers in general

Question asked by AndyB on Jun 27, 2012
Latest reply on Jul 2, 2012 by jstaley

I'm working on an ion detector for a time-resolved mass spectrometer.  The detector will employ a simple Faraday cup.  Expected ion currents are in the range of 10 fA to 1 pA with a bandwidth of approximately 50 kHz.


The bandwidth makes this a difficult problem.  For DC or low bandwidth applications a high-gain transimpedance amplifier is typically used.  For our application a charge integrating amplifier is more appropriate.


The AD8488 has a charge amplifier front-end (well, 128 of them).  Its minimum feedback capacitance of 0.45 pF would give us the gain we need. Can the AD8488 be used as a single-channel charge integrator with a reset every 5 ms?


Besides the AD8488, are there amps which are appropriate to this application (e.g. FET input, very low input bias current, very low noise)?  Some off-the-shelf solutions (often called "charge sensitive preamplifiers") are hybrids that employ a discrete input FET (sometimes cooled).  Any suggestions in this regard would also be appreciated.