Results of the Prototype Test: Cross Talk Measurements 
         ======================================================

                     by Marco Staric  (14-09-98)

 
  I'm sending the results of crosstalk measurements of the 'zero'
version of HV board. The PCB drawing is in the attached file. The PCB
board used for tests is only a half of HV board - consisting of mid
(ground) and bottom layer. Only the last four capacitors on the right,
input connector (2mm pitch) and the first output connector (two rows of
pins) have been mounted on the board. In addition second row of output
pins is grounded. The numbering of channels used below starts at the
right (ch 1) and runs to the left. Channels 1 3 5 7 are connected to ASD
channels 15 14 13 12 via HV capacitors. Channels 2 4 6 8 have only input
pins and would go on the missing top layer to the second connector.
  For the measurement I've used the analog output, ch. 14 of the ASD
board, i.e. measuring the pulse height on 400 MHz analog scope
(Tektronix). The signal was generated by Ortec 419 precision pulse
generator using charge terminator on generator's output. The coax (LEMO)
cable, 16ns long, was on the HV board side terminated by 50 ohm. The
charge was injected into the board thru 1 kOhm decoupling resistor. The
output signal is approx. 20 ns long with 7 ns peaking time and negative.
The crosstalk signal is bipolar, starting with negative polarity. Both
parts are typically 10 ns long. 
  First I've measured the linearity of the ASD8 analog output, using
well calibrated attenuation switches of the pulse generator:
 
ATTENUATION     OUTPUT (mV)
 
40              9.8
20              19.6
10              36.8
5               61.5
2               75.5
1               76.5
 
==> linear up to 30 mV.
 
The crosstalk was measured at the attenuation = 1, which corresponds to
PH=392 mV. Because pulse height (and the length) depends also on
capacitive load on the preamp input, for each setup this measurement has
been repeated. 
  Three different setups have been measured: 
        (A) ASD board connected directly to the HV board
        (B) same as (A) plus 18 pF capacitors added to HV board inputs.                    
            The grounded Cu foil was applied between capacitors to prevent
            crosstalk here.
        (C) ASD board connected to HV board via 50 cm long twisted pair                    
            cable plus 18 pf capacitors on HV board input.
 
Extrapolated pulse heights at attenuation =1 are 392mV (A), 332 mV (B)
and 218 mV (C). The pulse width has increased from approx. 20 ns to
approx 40 ns. Also the noise has increased by roughy 50 % (With a well
done shielding and a proper grounding I've observed only a white
preamplifier noise). 
  The results:
 
channel         (A)     (B)     (C)
 
1               2.7%    0.9%    7.1%
2               7.3%    3%      4.6%
3 (signal)      100%    100%    100%
4               8.2%    3%      4.6%
5               2.2%    0.6%    5.7%
6               0.7%    2.3%    3.9%
7               0.8%    /       0.5%
8               <0.3%   /       /
 
For the comparison I've also measured the crosstalk of the old HV board
having 18 cm long coaxial cables. On the middle left connector I've got:
 
channel         (D)     (E)
 
15              3.1%    1.9%
14 (signal)     100%    100%
13              2.6%    1.3%
 
(D) without (E) with 18 pF on the HV board inputs.
Signal: 290 mV (D), 240 mV (E)