PAL termination problem?

Question

I have a circuit like this.

Input of circuit is PAL signal. Output of circuit whose AC coupled version.
Input

Output

But HSYNC part in the output looks like mirrored. It should be more negative than burst part.
Where is my problem? Why signal distorted?

I scoped again the signals:
Before the C1 capacitor & After the C1 capacitor

Both signals have same 1V magnitudes. But DC avarages are different from each other.
This is HSYNC zoomed:

This is CAMERA just hasn't connected to PCB(disconnected from PCB)

There is no "inverting property" on oscilloscope channels.

PCB image

Exactly what 'decoder' device is the signal going into? Please both signals on the same scope screen so we see the correlation. — Bruce Abbott, Nov 05 '19 at 08:01
Renesas are reviewing my request and will send me the datasheet if I qualify! — Bruce Abbott, Nov 05 '19 at 08:34
Do you think the problem is related to Decoder? I think, it could be a termination or impedence matching problem. — Berker Işık, Nov 05 '19 at 08:46
For your circuit to work the decoder needs to have high input impedance with DC restoration referenced to the bottom of the sync pulses. The inverted waveform seems impossible (should be the same on both sides of the capacitor, apart from DC level), but I notice the amplitude at the camera side is much too high (should only be 1Vpp if properly terminated). This may be overloading the decoder, but it's hard to tell without seeing simultaneous traces of input and output. — Bruce Abbott, Nov 05 '19 at 09:05
I've added a simultaneous measurement trace. Signals looks like inverted. — Berker Işık, Nov 05 '19 at 15:51
What are your trigger Type setting again? Is it Video? If it is, what is the polarity setting? Is it negative like in your second picture? — Justme, Nov 05 '19 at 17:17
Also cover the camera so there is no other signal than sync, colorburst and black level. — Justme, Nov 05 '19 at 17:37
As well as being inverted the signal looks noisy when connected to the PCB. Are you sure the cable is connected the correct way around? Please show a photo of the wiring. — Bruce Abbott, Nov 05 '19 at 18:16

score 1 · Answer 1 · answered Nov 05 '19 at 09:17

1

This is an issue of scope settings. You have selected inverted polarity on the scope which puts the signal upside down. Use the non inverted polarity.

answered Nov 05 '19 at 09:17

Justme

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score 0 · Answer 2 · answered Nov 06 '19 at 11:33

Unfortunately, the problem was so simple. It is a reverse connected Video connector.
Like a measurement a signal with inverted probes multimeter. This comment "This may be overloading the decoder" made me think and led.

So thanks the points you've helped

PAL termination problem?

2 Answers2