R8 parallel capacitor #22

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opened 2023-09-19 14:34:33 +08:00 by sb10q · 2 comments
Owner

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.
Member

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)
Author
Owner

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.
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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