1. the actual gain for the VTX preamp signal at an attenuation of 10 db was 1.33.
2. At signal attenuation setting of 0 db some signal distortion/compression ( 30 % compression ) was observed indicating more input attenuation may be desired.
3. The signal monitor output was compared to the
comparator input and found to match closely when the factor of two
is taken into account.
4. Since the VTX preamp output risetime is specified as 5 nsec ( 10
- 90% ) one would expect the walk using this leading
edge discriminator to be around 5 nsec.
0 db - 10 db
1.0 nsec
0 db - 20 db
2.4 nsec
0 db - 30 db
4.5 nsec
5. Output pulse widths and leading edge jitter.
0 db
44.8 nsec ( see fig. 5 )
0.3 nsec ( see fig. 6 )
10 db
36.4 nsec ( see fig. 7 )
0.4 nsec ( see fig. 8 )
20 db
29.1 nsec ( see fig. 9 )
0.7 nsec ( see fig. 10 )
30 db
20.0 nsec ( see fig. 11 )
1.1 nsec ( see fig 12 )
6. For new design, the " 116 " IC should be replaced by an amplifier which will give a gain of around six without output saturation to give more accurate pulse widths and lower jitter.
7. The comparator circuit seems to work well.
1. the actual gain for the VTX preamp signal at an attenuation of 10 db was 0.85. ( see fig. 13 )
2. At attenuation setting of 0 db no signal distortion/compression was observed . ( see fig. 14 )
3. The signal monitor output was compared to the comparator input and found to match closely when the factor of two is taken into account. ( see fig. 15 )
4. Since the VTX preamp output risetime is specified as 5 nsec ( 10
- 90% ) one would expect the walk using this leading edge discriminator
to be around 5 nsec. ( see
fig. 16 )
0 db - 10 db
1.1 nsec
0 db - 20 db
2.8 nsec
0 db - 30 db
6.0 nsec
5. Output pulse widths and leading edge jitter.
0 db
35.5 nsec ( see fig. 17 )
0.3 nsec ( see fig. 18 )
10 db
29.5 nsec ( see fig. 19 )
0.5 nsec ( see fig. 20 )
20 db
22.3 nsec ( see fig. 21 )
0.9 nsec ( see fig. 22 )
30 db
11.9 nsec ( see fig. 23 )
2.6 nsec ( see fig 24 )
6. This circuit is not as good as the " 116 " modification, except for
lower distortion at the higher amplitudes, due to low gain. For new design,
an extra stage of EL2140 or a different circuit with more gain would give
improved results.