Requirement: Small Signal Linearity
When a signal swing of less than 10% of the SCA signal range is applied to the SCA input terminals the resulting differential readout signal swing shall deviate from linearity by less than 1%.
Good linearity is needed for the range near minimum ionizing response to avoid degrading position resolution.
Requirement: Large Signal Swing
When a signal swing of 10% of the SCA signal range or larger is applied to the SCA input terminals the resulting differential readout signal swing shall deviate from linearity by less than 4%.
Linearity for large signals (where S/N ratios are larger) can be corrected. Therefore the large signal linearity specification can be more relaxed than small signal linearity.
Requirement: Differential Gain
The ratio of the output signal swing to input signal swing over the SCA signal range shall be between 0.9 and 1.1, but shall be within 0.1% from channel to channel. Preferred sense of the gain shall be the same as for the PASA response to charge magnitude at the PASA input.
The range of driver amplifiers and ADC is limited. A range of 0.9 to 1.1 is needed to avoid signal overload while preserving optimum dynamic range. A tolerance of 0.1% is needed to be able to measure charge accurately without correcting for each channel of the SCA device. The SCA output should vary directly as the amount of charge measured at the PASA input to take advantage of lower power dissipation afforded by low occupancy. Thus if the PASA inverts the signal such that a high PASA output voltage represents low charge, the differential SCA gain should be negative so that a high input voltage is converted to a low input voltage to represent low charge.