Confidence Calibration Chip-known capacitors for charge injection and others for noise measurement

The Confidence Calibration Chip has two functions. The main one is to inject a known charge onto the input of detector amplifiers. This will enable the gain of these amplifiers to be calibrated. The second function is to simulate various detector capacitances so that noise against input capacitance performance can be measured. For the first function a voltage is applied to one plate of a nominally 50 fF capacitor, with the other plate attached to the input of the amplifier on the chip being tested. This can be done for up to 128 channels on a 44 μm pitch. The chip is designed so that one can determine to within narrow tolerances the value of the capacitors used for charge injection. This is done by measuring test structures. The gain of the channel on the chip being tested can then be found to within this tolerance. For the second function six capacitors are available ranging from (nominally) 5 pF to 50 pF. These will enable a plot to be made of noise figure vs input capacitance for channels on a detector chip. The chip requires no power supply, only ground. This reduces the chances of noise injecting onto channels and spoiling measurements. It has been bonded to an MX7 chip for evaluation. This paper describes the design and testing of the chip