CDC 12 12 2007

Interposer, preAmp, and signal cable

The new preAmp, the interposer, and the signal cable arrived at CMU. The first test that was performed was to apply 3.2 V on the preAmp board without anything connected to it: the board drew a current of 280 mA, this is ecact the current that is specified, good! After connecting the signal cable to it the current that was drawn doubled, not so good. It turned out the the piece of signal cable sticking out of the connector was touching the heat sink and making shorts. After cutting off this piece of cable the preAmp was again drawing 280 mA.

Channel 1 and 2 of the signal cable were connected to our postAmp and all the other channels were left open. When the preAmp is NOT connected to the HV distribution board a noise(?) signal can be observed on the scope (shown in figure 1). [Image:preAmp-out-notconnected.jpg|thumb|none|400px|figure 1: PreAmp output signal(s) observed when it is not connected to the HV distribution board.]] When connected to the HV-distribution board the output signals looked like an 10 MHz oscillation. The signal seen on the oscilloscope is shown in figure 2. [Image:preAmp-out-connected.jpg|thumb|none|400px|figure 1: PreAmp output signal(s) observed when it is connected to the HV distribution board.]] This does not look like CDC signal. Another short was suspected.

Pedestal measurement

A pedestal measurement was done with the pre-amplifiers not connected to the CDC. The width of the pedestals is around 10 ADC-channels. The width of the pedestals (with common mode noise subtraction) of the whole system is 40 channels. The width of "raw" pedestals is 150 channels