E.Atkin, Yu.Mishin, Yu.Volkov
Moscow Engineering Physics Institute, Russia
!!
A number of LHC experiments (for instance, ones with time-of-flight 
detectors) require high-speed (wide-band) splitters of photomultiplier analog 
signals. The splitters should have high slew-rate (up to 2000 V/us), large 
dynamic range (up to 60 dB) and low power consumption (tens of mW). The 
main destination of the splitters is to provide simultaneous parallel signal 
processing by amplitude, charge, time and so on. The splitter can drive CFD, 
LED, ADC, QDC, TDC and so on.
        The most acceptable circuital solution in this case is the use of 
push-pull AB stages with complementary bipolar transistors.
        The elaborated splitter circuit contains an input section (core) and an 
output buffer stage.
        The core is built according to the current feedback schematics and is 
responsible  for bandwidth  and static parameters (input offset voltage and 
input currents). The latter set a limit to the dynamic range. Taking into 
account disturbances, cross-talks and the standard offset voltage for a pair of 
bipolar transistors to be ~1..2 mV, one should assume minimal input signals 
of ~5..10 mV.  In order to provide 60 dB of dynamic range there must be 
ensured a maximal output amplitude not less  than 5V.
        The output buffer stage  (compound voltage follower) provides 
driving low-ohmic loads. The value of fan-out (output stages operating in 
parallel), can vary from 1 to 5 depending on the total load.
        The photo of the manufactured prototype printed circuit unit (PCU), 
based on microwave transistors and fitted with LEMO connectors, is 
presented. The dimensions of the PCU are 75*50 mm.sq. This version 
provides operation at a unity gain and a fan-out of 4 at load resistances of 50 
Ohm each. The maximal output amplitude thereat makes up at least 5V. 
Rise/fall times are within 2.5 ns. Signal polarity can be any. The maximum 
rate is 200 kHz. Offset voltage for each output does not exceed +- 3 mV. At 
supply voltages of +-10V power consumption is 250 mW/channel.
        Considering high speed  and bandwidth (above 100 MHz), along with 
circuital matters much attention should be paid to mechanical design 
implementation. Therefore simulation was done taking into account the 
influence of the design reactances of PCB conductors and pads on the 
electric parameters.
        At present the task of miniaturizing the splitter is being solved. It is 
expected to implement the tested circuitry in the form of a semicustom IC. It 
is planned  to supplement the circuit with a gain control for separate splitter outputs and 
an electronic adjustment of DC output potentials, aimed at setting them close 
to zero as possible.
!!
The high-speed (wide-band) splitter circuit for reading-out photomultiplier analog signals is described. The splitter can simultaneously drive loads of the type of CFD, LED, ADC, QDC, TDC and so on.   The photo of the manufactured prototype printed circuit unit (PCU),  based on microwave transistors and fitted with LEMO connectors, is  presented. The dimensions of the 4-channel PCU are 75*50 mm.sq. The splitter provides a high slew-rate of about 2000 V/us, large dynamic range up to 60 dB and low power consumption 250 mW.
!!