Electronics > Projects, Designs, and Technical Stuff
62.5kHz ringing Noise on signal
syntax333:
Hi,
The project that I am working on is to transmit video stream through visible light. The schematic of receiver circuit is shown in attachment.
Received signal which is transmitted through visible light is converted into voltage with help of OPA657 then I clamped the signal to ground level and finally buffered.
This schematic works in breadboard design.
However, In PCB design there is always ringing on signal which disturbs the signals color.
PCB layout is also in attachment.
62.5kHz ringing on signal is shown in DS1Z_QuickPrint135.png.
Is there any suggestions?
Thank you in advance.
stj:
interesting, the frequency falls into the range of most modern switching psu chips.
have you checked the enviroment for "contamination" ?
Andy Watson:
The ringing has a repetition rate of 62.5KHz but the frequency of the actual ringing looks to be much higher. Those high-bandwidth op-amps are very sensitive to capacitance around their inputs - you've got some "long" traces runing parallel to the ground plane. "Visible light" - does that mean that one of those inputs is connected to a photodide ? - Remember to factor the capacitance of the diode into your design.
Also, how are you probking the signal? Your oscilloscope probe will add a few pf to the circuit - it's often useful to isolate the probe by placing a 100 resistor at the probe tip. And use the short stubby probe ground clip too.
StillTrying:
Are you sure it's not coming from the 555 -9V generator, although its frequency should be about 48kHz with those values. Its 3200uF cap seems a very large, probably too large to suppress fast switching spikes.
I've just realised that 15,625*4 = 62,500 which might help to give a clue, or not, to where it's coming from.
duak:
Isn't 15,625 Hz a horizontal scan rate for a television operating on 50 Hz? Could there be a CRT or LCD display close by generating the 62.5 kHz as a multiple of 15,625 Hz? It soulds like the circuit may be sensitive to stray light of some sort.
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