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R8 parallel capacitor #22

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opened 2023-09-19 14:34:33 +08:00 by sb10q · 2 comments
sb10q commented 2023-09-19 14:34:33 +08:00
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Prototype was found with 160pF capacitor in parallel with R8. Find out why that capacitor was there and whether we should include it.

Prototype was found with 160pF capacitor in parallel with R8. Find out why that capacitor was there and whether we should include it.
linuswck commented 2023-10-20 12:34:43 +08:00
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Doing a spice simulation on the circuit shows that this capacitor passes through high frequency components more than without. I think that should not be included. I do not know the original intention for this modification.

Point of Measurement:
Modulation Input is GND-ed
image

Frequency Response Curves (0-100MHz)
Without the capacitor connected:
image

With the capacitor connected:
image

Doing a spice simulation on the circuit shows that this capacitor passes through high frequency components more than without. I think that should not be included. I do not know the original intention for this modification. Point of Measurement: Modulation Input is GND-ed ![image](/attachments/9715c62e-6808-4cb1-a114-fe9f768ccbd6) Frequency Response Curves (0-100MHz) Without the capacitor connected: ![image](/attachments/021941e5-8415-4a6b-bd82-2d3bdd73542b) With the capacitor connected: ![image](/attachments/b47ef2e1-366f-471d-afce-c845ff8cc859)
image.png
162 KiB
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97 KiB
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164 KiB
sb10q commented 2023-10-20 16:05:23 +08:00
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I see, that makes sense. There was some work to increase the modulation bandwidth. I think the capacitor should be kept and its footprint added to the PCB.

I see, that makes sense. There was some work to increase the modulation bandwidth. I think the capacitor should be kept and its footprint added to the PCB.
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sb10q closed this issue 2024-01-23 17:18:59 +08:00
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Reference: sinara-hw/kirdy#22
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