A 16-channel continuous charge amplifier with sparse readout

A low-noise low-power 16-channel preamplifier/shaper IC designed at the Rutherford Appleton Laboratory (RAL) in 1.5 μm CMOS is described and the results obtained from the testing of the manufactured IC are presented. The IC was designed for the readout of the photodiodes which detect energy deposits in CsI scintillation bars. Each channel amplifies the input charge from a photodiode and shapes it with a 5 μs time constant (a requirement of the detectors). The peak of the shaped signal is held by a peak-hold amplifier and stored onto a holding capacitor for readout. Each channel includes its own comparator used to identify data for readout. A Data Ready flag is output when any of the channel comparators switches, indicating a “Hit”, and the peak voltage, along with digital addresses of the “Hit” channels, are read out. Two readout modes are available, one allows only those channels with “Hit” comparators to be read out, while the other allows all 16 channels to be sampled simultaneously and read out, regardless of the state of the comparators. In each case analogue data is read out in series. A channel noise of 330 electrons ENC RMS plus 6 electrons/pF of detector capacitance has been achieved using 8 mW of power per channel with a 5 V supply. Pulse height distributions for the selected sources detected using a prototype system will be presented along with a brief description of the system.