Description: Fig50 , Filename: fig50.epsPostamp/Discriminator - First Stage Prototype Tests Burr-Brown OPA680 opamp tests Output minimum width settings 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
Postamp/Discriminator - First Stage Prototype Tests
OPA680 Opamp and Output Minimum Width Setting
Some tests of the inverting opamp circuit were done at
three gain settings using an alternative opamp, the
Burr-Brown OPA680 which is cheaper than the OPA689 used
in the previous tests.
1. Set for Gain of 6
a). The measured gain for the VTX pulse was about 8 %
low indicating that there is not enough bandwidth
available at this gain. This could lead to variation
in gain between channels.
b). The noise and crosstalk of this postamp circuit was
8 db better than the preamp, which is the same as
the single-ended ECL and the inverting OPA689 values.
Note: Correction on reported value for previous opamp
test. 40 db minus 32 db is 8 db not 12 db. The
differential ECL circuit is best at 10 db. The
inverting opamp circuit is worst at 5 db.
2. Set for Gain of 4.3
a). The measured gain for the VTX pulse was also about
8 % low.
b). The crosstalk and noise factor improved to 9 db
3. Set for Gain of 2 . [ The threshold divider resistor
at the comparator input was changed to 51.1 ohms to
match the signal range. ]
a). The measured gain was 2.6 % low. i.e within resistor
tolerance.
Fig 49 Full Scale input 2 db setting
Fig 50 12 db setting
b). The crosstalk factor stayed at 9 db.
c). Output Widths 35.32, 31.44, 26.05, 17.18 nsec
[ adding a 50 pf width adjusting capacitor
adds about 6 nsec to these numbers ]
Fig 51 Jitter versus input amplitude
d). Output Leading Edge Jitter versus input amplitude
Fig 52
Output Minimum Width Setting
The gain of two circuit was used to investigate the
output minimum width. First the threshold was adjusted for
no crosstalk. Then the minimum input for reliable output
was found.
Fig 53 signal levels at setting of 33 db , ~ 10 mv
Fig 54 Output at 33 db setting - self-triggered to
show pulse width envelope [ 50 pf ]
Fig 55 Output at 35 db setting showing output on low
signal and noise which will give widths
from one nsec up. These outputs are not
usefull since they are below the level of
the crosstalk. Any width less than 10 nsec
will not have both edges properly recorded
by the TDC.
Fig 56 The Output adjusting capacitor was changed to
30 pf so that the smallest signal of
interest has a width just over 10 nsec,
thus ensuring that all signals of interest
are recordable for riseing and falling
edges.
[ 33 db setting shown ]
Widths for 2 db 12 db 22 db 32 db 33 db
38.28, 33.62, 26.96, 14.57, 12.60 nsec
Description: Fig49 , Filename: fig49.eps
Description: Fig50 , Filename: fig50.eps
Description: Fig51 , Filename: fig51.eps
Description: Fig52 , Filename: fig52.eps
Description: Fig53 , Filename: fig53.eps
Description: Fig54 , Filename: fig54.eps
Description: Fig55 , Filename: fig55.eps
Description: Fig56 , Filename: fig56.eps