... | @@ -8,19 +8,23 @@ and the following one with the other logic value. But it would be |
... | @@ -8,19 +8,23 @@ and the following one with the other logic value. But it would be |
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impossible to determine when did this change occur within the sampling
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impossible to determine when did this change occur within the sampling
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period. Interpolation is required. To do this, the idea is to convert
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period. Interpolation is required. To do this, the idea is to convert
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the rising/falling edge of the pulse in a longer observable event. In
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the rising/falling edge of the pulse in a longer observable event. In
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our case, we transformed the pulse falling edge into a damped sine wave.
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our case, we transformed the pulse falling edge into a damped sine wave,
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Thanks to fitting techniques, it is possible to determine the phase of
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impulse reponse of an LC filter. Thanks to fitting techniques, it is
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this signal and, consequently, its time of arrival. When the time of
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possible to determine the phase of this signal and, consequently, its
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arrival of the different pulses are known, the delay between them can be
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time of arrival. When the time of arrival of the different pulses are
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computed by computing their time of arrival difference.
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known, the delay between them can be computed by computing their time of
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arrival difference.
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This page is dedicated to the built filter which converts the pulses
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This page is dedicated to the built filter which converts the pulses
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edges into damped sines. The filter for one channel is represented in
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edges into damped sines. The filter for one channel is represented in
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figure 1. The used operational amplifier is a LMH6624 and the schottky
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figure 1. The used operational amplifier is a LMH6624 and the schottky
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diodes are HSMS-281C-BLKG. This filter is designed to convert the
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diodes are HSMS-281C-BLKG. This filter is designed to convert the
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falling edges into damped sine. The diodes can be reversed to convert
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falling edges into damped sine. The diodes can be reversed to convert
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the rising
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the rising edges. The schematics does not represent the decoupling
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edges.
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capacitors around the operational amplifier. We used a combination of
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1uF 100nF and 1nF X7R capacitors on both the positive and negative
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inputs to do the
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job.
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![](/uploads/b0ba733fb34ff727efbf1aafdbcfef22/filter.png)
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![](/uploads/b0ba733fb34ff727efbf1aafdbcfef22/filter.png)
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*Figure 1 - Filter schematics*
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*Figure 1 - Filter schematics*
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... | @@ -44,6 +48,14 @@ addition of this resistor. |
... | @@ -44,6 +48,14 @@ addition of this resistor. |
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The actual filter is built with a nickel-zinc ferrite coil with a 1.5 mH
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The actual filter is built with a nickel-zinc ferrite coil with a 1.5 mH
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inductance and a 100 pF capacitor X7R.
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inductance and a 100 pF capacitor X7R.
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It is also mandatory to be independant of the incomming signal shape and
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level. To do that, we use CMOS gates. On one hand they will always give
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the same output once the input becomes higher than the threshold level,
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we will then always have the same damped sine shape. On the other hand,
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they clean the edge. As the LC impulse response is linked to the quality
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of the pulse, we clean then the damped sine shapes and improve the
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fitting results.
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-----
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-----
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6th of December 2016 - Nicolas Boucquey
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6th of December 2016 - Nicolas Boucquey
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