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.