Description: Fig2 , Filename: Fig2.epsPostamp/Discriminator First Stage Prototype Tests, Part 1 this is a reposting attempt 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
E614 Postamp/Discriminator - First Stage Prototype Comparison
By investigating the proposed circuits with fast risetime pulses, some circuit changes were developed aimed mainly at reducing crosstalk. These changes were made before the following tests were undertaken.
1. There was crosstalk between the two sections of the comparator due to the enable circuit even though there are separate enable inputs. Permanently enabling both channels stops this with no observable disadvantages.
2. Lowering the impedance at both comparator input polarities to about 100 ohms seems to reduce crosstalk dramatically. This means that the threshold circuit becomes an attenuator and requires some current. The threshold trimpot cicruit was changed to provide this.
3. It was found that the series output resistor for the inverting amp stage was not needed.
Note: The capacitor which adjusts the minimum output width was removed for these
tests to more easily show the relation between input pulse width and output.
A. Characteristics of VTX Preamp Output at input to cable and at postamp input with termination consisting of 1 K and ac coupled 53.6 ohm only.
( no connection to first stage )
Fig 1. Shows Full Scale signal. [ 2 db attenuator setting in test setup ]
Cable attenuation - 412 mv input , 360 mv output = 1.33 db
Cable Delay - 19 nsec
Fig 2. Crosstalk at preamp output with channel 2 Full Scale input.
Ref 3 is Ch 1 - 3 mv vs. 412 mv 43 db
Ref 4 is Ch 3 - 4 mv vs. 412 mv 40 db
Fig 3. Crosstalk at postamp input with channel 2 Full Scale input.
Ref 3 is Ch 1 - 3 mv vs. 360 mv 41.6 db
Ref 4 is Ch 3 - 4 mv vs 360 mv 39 db
Fig 4. Noise level at preamp output and postamp input of channel 1
with Channel 2 Full Scale input to show noise relative to crosstalk.
Ref 3 Ch 1 preamp out 7 mv pk
Ref 4 Ch 1 postamp input 7 mv pk
Note: This is the noise level of the FET probe used, Tektronix P6243.
B. ECL receiver first stage with single ended coupling to the comparator input.
Channel 2 of postamp driven
Fig 5. Shows input waveform compared to stored waveform of Fig 1.
This shows good input termination even at Full Scale input.
Fig 6. Linear Amplification [ 12 db attenuator setting ]
Ch 1 comparator input - 184 mv gain 184/112 = 1.64
Ch 3 output of channel 2 from ECL to NIM translator
Math 3 inverted and scaled Ch 1 for comparison with R 2 stored input
waveform from Fig 1.
Fig 7. Saturated Amplifier. Same setup as Fig 6 with Full Scale input
[ 2db attenuator setting ]
Inverted waveform is scaled to match the stored waveform risetime.
Shows recovery time from saturation
Output saturates at 250 mv.
Fig 8. Crosstalk and Noise at comparator input of channel 1.
Ch 1 crosstalk 7 mv.
R 3 noise 8 mv pk
Ch 3 channel 2 output
Note: This is the noise level of the FET probe used, Tektronix P6243.
Fig 9. Shorted Ch 2 input showing very low crosstalk
Note: This is the noise level of the FET probe used, Tektronix P6243.
Output Pulse Width versus input amplitude measured by Timer/Counter after
threshold adjusted to give 26 nsec width at 22 db input for comparison
with inverting opamp circuit. ( set at 11.2 mv )
32 db 16.55 nsec
22 db 26.03 nsec
12 db 31.90 nsec
2 db 36.85 nsec
C. ECL receiver first stage with differential coupling to the comparator.
Channel 4 driven
Fig 10. +/- comparator input - linear amplification [ 12 db attenuator setting]
Fig 11. +/- comparator input - saturation [ Full Scale input 2db setting]
Fig.12. Channel 3 crosstalk
Fig 13. Channel 3 crosstalk - input shorted
D. Inverting Opamp first stage - Channel 1 & 2 Av = 6 - Ch 1 driven
Fig 14. Input termination compared to stored waveform
Fig 15. Comparator input at Full Scale
Fig 16. Crosstalk at Ch 2
Fig 17. Crosstalk at Ch 2 - input shorted
Linearity of Channel 1 - DSO Ch1 input, Ch 2 Comparator scaled to match M 3,
M 3 Ch 1 invert
Fig 22. Full Scale input - 298 mv/50 mv = Av = 5.96
Fig 23. 12 db setting - 150/25 = 6.0
Fig 24. 22 db setting - 60/10 = 6.0
Fig 25. 32 db setting - 60/10 = 6.0
Output Pulse Width versus input amplitude at 5 mv threshold re: input
[ set at 5mv X 6 = 30 mv ]
Output width measured by Philips PM6654C timer/counter
Fig 26. 32 db 16.5 nsec
Fig 27. 22 db 26.0 nsec
Fig 28. 12 db 31.64 nsec
Fig 29. 2 db 35.7 nsec
Output Pulse Jitter versus input amplitude
Fig 30. 32, 22, 12, 2 db
E. Inverting Opamp first stage - Channel 3 & 4 Av = 12 - Ch 4 driven
Fig 18. Input termination - clamping Full Scale input and linear input
versus stored waveform.
Fig 19. Comparator input at FullScale ( showing clamping ) and linear operation
versus stored waveform.
Fig 20 Crosstalk Ch 3
Fig 21 Crosstalk Ch 3 - input shorted
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