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Unfiltered
Filtered
Results
Setup | Measured Frequency (MHz) | Unfiltered Vpk-pk | Filtered Vpk-pk | Suppression factor ([Unfiltered Vpk-pk]/[Filtered Vpk-pk]) |
|---|---|---|---|---|
| Unity Amplifier (2.2M Resistors) | 27 | 7.44 | 2.16 | 3.44 |
| Unity Amplifier (100k Resistors) | 7.44 | 1.20 | 6.2 | |
| Unity Amplifier (100k Resistors + 0.1uf decoupling capacitors) | 7.5 | 2.56 | 2.93 | |
| Bypass Capacitors only (0.1uF Capacitors) | 5.92 | 3.04 | 1.95 |
The conclusion so far
So far it seems that the Unity amplifier set up is the best at suppressing EMI noise in a common mode-rejection setup. Interestingly, by reducing the resistor values the amplifier was better at suppressing the EMI noise. But adding decoupling capacitors add little to no affect (if not worsen) to the EMI suppression. My current speculation is that the lower variation on resistance allowed better resistor matching, thus improving the rejection of EMI. Next time I would like to try lower tolerance resistors and another common-mode rejection setup that uses a ferrite choke coil instead.
Button Debouncing
Abstract
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The capacitor used in this circuit is a 10000Pf capacitor:
The circuits were further modified to incorporate schmitt triggers, the schematics shows the new circuits:
In circuit 5, a TLV324IDCKR Schmitt trigger was used with an sot-23 breakout board. For Circuit 6 (using an inverting schmitt trigger), an op-amp circuit was used.
Measurements
Circuit 1: Unfiltered Switches
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By having R1=10k and R2=380k the results have definitely improved. The result is a much smoother curve, but we some oscillations are still present in the curve. The circuit could be further improved with the use of a schmitt trigger.
Circuit 5: Using the non-inverting schmitt trigger
The model used for the non-invertive schmitt trigger was the 74LVC1G17SE-7 single schmitt trigger in a SOT-353 package
Button
Strange, there is a lot of noise during the falling edge of the output.
II repeated the test using C1=1000pf and 0.2uf but the results were the same:
I suspect that either, the configuration for this circuit is incorrect or the model of the op-amp I was testing (74LVC1G17SE) was inappropriate for this application.
Circuit 6: Using an inverting schmitt trigger
The inverting schmitt trigger was made using a TLV314IDCKR Op-amp. The schematic shows the configuration:
R1=R2=R3=2.2M, Vref=VCC=5v, VEE=GND
This configuration is an asymetric schmitt trigger configuration with two seperate voltages for HIGH and LOW respectively.
For this debouncing circuit, C1=0.1uF
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Definitely a far cleaner signal than the previous configurations. It should work reliably for any switch input. I decided to try different resistor values for the debouncing circuit. So far the results are almost identical:
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