12/ 11 /1998

Haifeng wu

1. Measuring the capacitance of PMT and voltage divider

The schematic set up for measuring the capacitor of PMT and voltage divider is shown below.



The frequency response curve of V2 Vs V1 was measured , using Hspice we can t find the exact inductance of L in test setup , and the total capacitor of PMT and voltage divider C0 . The measured parameter of L was consistent with the value measured in earlier work. The value of in question capacitor C0 = 31PF.

2. The influences upon shaper output by capacitance of PMT and voltage divider

In order to estimate the influence of the capacitance of the PMT and voltage divider upon the shaper output, firstly we demonstrate the output waveform of initially balanced shaper of 3_in_1 card No.115 in figure 1.

Figure 2 is the output wave of shaper while the card was connected with PMT block, due to the additional capacitor of PMT block, the shape has a longer tail and a reduced amplitude 910mv compared with the initial 970mv. Figure 3 shows the shape of output of 3_in_1 card after 31PF capacitance was reduced from shaper, from where we can see that when the capacitance of first stage of shaper was reduced 31PF, the amplitude of the shape increased 8% to 1050mv, and the overshoot increased to about 1%. Figure 4 is the waveform of same card with reduced capacitor after connecting to PMT block. Where the shape and amplitude of output is same as figure 1. It means that if we deduct the capacitance of PMT block from the first capacitor of initial shaper and assemble PMT block and 3_in_1 card , the total capacitor of the shaper will remain the same and the shaper will return to initially normal operating condition.

 



Figure 1. The initial performance of shaper.



Figure 2. The output of 3_in_1 card after connecting to PMT block



Figure 3. The performance of shaper after reduction of 31PF



Figure 4. The shape of output of same card as Figure 3 connected with PMT block

 

3. Conclusion