... | @@ -12,5 +12,35 @@ our case, we transformed the pulse falling edge into a damped sine wave. |
... | @@ -12,5 +12,35 @@ 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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Thanks to fitting techniques, it is possible to determine the phase of
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this signal and, consequently, its time of arrival. When the time of
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this signal and, consequently, its time of arrival. When the time of
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arrival of the different pulses are known, the delay between them can be
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arrival of the different pulses are known, the delay between them can be
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computed by computing their time of arrival difference
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computed by computing their time of arrival difference.
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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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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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falling edges into damped sine. The diodes can be reversed to convert
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the rising
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edges.
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![](/uploads/b0ba733fb34ff727efbf1aafdbcfef22/filter.png)
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*Figure 1 - Filter schematics*
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The capacitor C1 is used to realise a high-pass with the rest of the
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circuit. On the rising edge, the capacitor C1 is charged through the D1
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and R2. D2 is in off-state and nothing arrives to the filter output.
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In contrast, on the falling-edge, the pulse discharges C1 through the
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D1, R3 and the filter. The shape of the impulse arriving in the
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LC-filter depends on the voltage difference of the pulse, the fall time
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and the size of the ratio C1 to C2. The R3 value is 100 Ohm to have an
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equivalent 40 Ohm input impedance on each pulses and then avoid
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reflections.
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The operational amplifier is used as both a buffer and an amplifier. Its
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gain is set to 2. The resistor R4 is added for the amplifier stability.
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The damping factor of the filter does not seem to be affected by the
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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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inductance and a 100 pF capacitor X7R.
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