Test circuitry includes two buses: first, for reference voltage (switched through printed 1 pF capacitor to the preamp input, thus allowing the variation of the preamp output amplitude) and, second, for triggering with TTL pulse. The reference voltage bus is a DC bus, one per panel side. The triggering bus (propagation line with impedance ~ 50 ohms printed on the PC board, terminated at the end) is supplied for a group of 24 preamp channels through a 2 Kohm resistor to the base of a normally closed n-p-n transistor with grounded emitter.
No longer using this concept, instead we are using a 400 MOhm current-limiting resistor. Max fault current per tube then is 12.5 uA.
N/A.
Resistors which properly match impedance of two x 8 cells tubes connected to the input of the preamplifier (as required by MuId operation) have been tried. For proper matching an additional serial resistor of 300 ohm was connected between tube and preamplifier (before ganging two tubes together). This resulted in noticable degradation of the preamp speed and consequently made the time spread worse by 10 ns. Thus, ~100 ohm input impedance of the preamp is a compromise between speed and matching. With 100 ohm preamp input each tube cell (propagation line with impedance of ~ 280 ohm) is terminated with 245 ohms giving 12% mismatch at preamp end. The other (passive) end of each tube will be terminated properly.
The neon lamp in the input protection circuit was replaced with a second bipolar Si-diode protection network. This is desireable because a preamplifier serves two tubes, so one tube could have a broken wire while the other tube could still be read out if the preamplifier is not destroyed by the wire breaking. The protection circuit was thoroughly tested to guarantee that the preamp continues to work despite any type of HV break down, including the severe case in which one of the connected tubes breaks a wire.
Protection diode's capacitance is in the range of 10 pf which is neglegible as compared to the values of decoupling caps 2.2 nF and LST tubes (in nF range).
Transition to +/- 5 or 6 volts would be in principle possible, but it would involve a new redesign and a new cycle of prototyping which can not be afforded within the present muID assembly schedule. In addition, since the amplification is based on the value of the resistor in the collector of the input transistor, lowering the power voltage (at the same preamp gain) will change the input transistor bias current and will potentially make response slower. To understand whether this is acceptable will require additional R&D work.
The large value capacitors (2 per each channel) were designed to reduce potential channel-to-channel crosstalk through power buses and provide better power noise filtering. The 22uF caps are expensive and, we lately discovered, do not have sufficient reliability. Tests have shown that in our multi-channel preamp system the 0.1uF caps are already adequate.
The final differential receiver which will operate with muID signals in PHENIX has not yet been designed. There is a CAMAC-resident differential receiver that has been designed to be used in the factory. This differential reciever includes passive analog filtering of the transmitted preamp pulses to improve signal/noise. Filtering includes AC coupling and integration with RC ~50 ns (integration time to be optimized by tests in realistic readout scheme). The output of analog reciever is unipolar AC coupled signal with rise time ~40 ns and FWHM ~200 ns for normal operational HV and gas.
With n-p-n transistor the output signal linear dynamic range is provided by the bias current of the n-p-n transistor (typically 15-16 ma), with p-n-p transistor it is not limited by the transistor regime and current in the output transistor can be brought to the optimal value ~2.5 ma.
The ground loop is DC, and therefore not a problem (except in the case of a very large signal). We have not observed a problem in any of our tests, but this is one of the reasons to have a good ground. See question 19.
We are going to use polyfuses for every preamp channel.
For proper operation low voltage should be in the following operation margins:
+12 V : from +11.5 to +13.2 V
-12 V : from -10.6 to -12.5 V
If both voltages are at 12.00 V then the gain variation coefficients are:
+7.2% / V (for each voltage)
Since we use AC coupling with RC ~ 5 us, this determines the G vs omega at low frequences. The output rise time is <~ 10 ns and depends on the resistors used for matching, chosen current gain (presently ~150) and type/length of the output cables etc. This suggests a bandwidth of ~30 MHz.
We don't know yet, what will be CMRR in the final design of the receiver (see point 9). In the analog receivers we are building for QA tests CMRR in a real differential mode is determined by CMRR of the input op. amplifier. For AD8001 (we are using) the CMRR is typically 54 dB in the specs. This figure might be better in our case, since we are not using the entire bandwidth of the device.
The RTV supplies structural support for our assembly of 4 6-channel boards, so we are planning to use it. We have tested Glyptal conformal coating and it was not entirely satisfactory. Single layer coatings were not always adequate. Applying multiple layers of a conformal coating and the additional QA required are potential schedule problems that we wish to avoid.
OK.
Done.
This is an additional grounding option provided in case grounding through signal and HV cables is found to be insufficient. Whether we will need to use this option will depend on the results of the tests with full prototype and realistic cable connection. We will not have the opportunity to provide additional grounding if panels are found to be noisy after RHIC turns on. See also point 11.