Postamp/Discriminator First Stage Prototype Tests, Part 2
   Some crosstalk measurements and Part change information

John Schaapman                     Ph: 780-492-3043
Centre for Subatomic Research     Fax: 780-492-3408
University of Alberta            NOTE: new area code
Edmonton, AB
CANADA       T6G 2N5

        Some Crosstalk Measurements 



ECL circuit

   A. Single ended coupling to comparator  Ch 1 & 2,   Ch 1 driven

          a.)   Threshold set for no crosstlk on Ch 2

                      - 13.09 mv    setting of  35 db for smallest signal to give Ch 1 output

                                           signal range is 33 db

b.) Shorted input to Ch 2

                 No crosstalk!

                 Threshold adjusted above noise on both channels

                              -5.35 mv lowest setting for output on Ch 1 43 db

          signal range 41 db

           This indicates that the postamp has 8 db better noise and crosstalk than the preamp and cable.



   B. Differential coupling to the comparator  Ch 3 & 4,  Ch4 driven

a.) Threshold set for no crosstalk to Ch 3

- 25.39 mv lowest setting for output on Ch 4 35 db

               signal range 32 db

b.) Shorted Ch 3 input

               No crosstalk!

               Threshold adjusted above noise for both channels

                  - 7.18 mv   lowest setting for output 44 db

                            signal range 42 db

This indicates that the postamp has 10 db better noise and crosstalk than the preamp and cable



Inverting Opamp circuit  Ch 1 driven

a.) Threshold adjusted for no crosstalk on Ch 2

- 46.25 mv  lowest setting for output Ch 1 34 db

                  signal range 32 db

b.) Shorted Ch 2 input

                   No crosstalk!

                   Threshold adjusted above noise for both channels

- 15.2 mv  lowest setting for output on Ch 1 42 db

signal range 40 db

               This indicates that the postamp has 12 db better noise and crosstalk than the preamp and cable.

        First Stage Prototype Changes



ECL line receiver circuit

  Enable cct.

     Remove C36,37,38,40      30 pf

      Remove R 53,55,56,57   5K1

      Replace  R46,49,51,54     820 with short

   Comparator + input impedance change

       Replace R36,37,42,43    1k0 with 90R9

    Threshold cct

        Replace R35,38,41,44 1K0 with 1K21 ( or 1K0 1 % )

         Replace R1 5K with 500

         Replace R2 5K1 with 243

         Add 12R from + trim R1 to GND

         Replace R3 with 51R1

    Ch1 & 2  for single ended coupling to comparator       

         Remove C18,20    10 n

          Add  90R9 ( prefer 100 1 % ) from negative comparator input to gnd

    Ch3 & 4 for differential coupling to comparator

         Leave C23,25 10 n

         Replace C21,28 10 n with 90R9 ( prefer 100 1 % )



Inverting Opamp cct

     Clamp ccts

         Replace R38 1k0 with 330

         Replace R39 100 with 330

         Replace R28 1K0 with 82R5

       Opamp output cct

         Replace R31,33,35,37 49R9 with a short

         Replace R40,41,42,43   470 with 90R9

       Enable cct

          Remove C46,44,45,47    30 pf

          Remove R62,60,63,61    5K1

          Replace R54,57,59,56    820 with short

       Threshold cct

          Replace R45,47,49,50  1K0 with 243 1 %

           Add      R88,89,90,91                  243 1 %

           Replace R1 5K with 500

            Replace R2  5K1 with short or Ferrite Bead

            Replace R3 5K1 with 243

            Add 3R3 to GND from + side of R1 trim

       Ch1 & 2   Av = 6

            Replace R 8,9   82R5 with  75

       Ch3 & 4   Av = 12

             Replace R 10,11 82R5  with 200

             Replace R 19,22  124  with 61R9

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