I all , this is what my spdif signal looks like at the differential receiver ( FIN1002) output , just before entering the DIR9001 , what could be the reason for such ringging ?
I forgot to mention that the signal is clean at the input , and the length of the trace between the two chip is 13 mm , 0.3 mm wide , I thought the trace could do that ?
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I forgot to mention that the signal is clean at the input , and the length of the trace between the two chip is 13 mm , 0.3 mm wide , I thought the trace could do that ?
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This is the layout of the pcb , U23 is the FIN1002 , U19 is the DIR9001 , the two resistors ( 10 k) from pin 4 of the FIN1002 to gnd and vcc are recomended by John , ringing is the same with and without those resistors
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I would check the voltages on both input pins of FIN1002 with your 'scope. Could be there's considerable common-mode content on those pins. The CMRR of the FIN1002 is an unknown.
Not sure this would help, but I'd like to see a bypass cap between the Vcc and the GND pins at the FIN1002.
The input signal is pretty square with almost no ringing , the measurement is made with the same probe at the same moment , there is an 0.033uf cap on the bottom layer between vcc and ground
I am out of town today , tomorrow I will measure the noise at the FIN input and try the Nattawa mod 😉
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I am out of town today , tomorrow I will measure the noise at the FIN input and try the Nattawa mod 😉
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I agree. Such a fast IC needs decoupling. Otherwise it can easily turn into an oscillator.
Is there a ground plane in the PCB? Again, for fast circuits like this, it is highly recommended.
The long wire from the GND pin of the FIN1002, and the other supply lines, means that there is a high inductance in the supply line, so that the 33 nF capacitor probably doesn't help that much. Put a capacitor very close to the IC as suggested by nattawa.
Perhaps a slightly slower receiver, with hysteresis on the input, would be a better choice than the FIN1002.
What type of oscilloscope probe did you use? I hope it was 10X not 1x.
Where did you connect the GND of the probe?
How did you connect the GND of the probe?
Did you use a short connection like the one in the picture or did you use the long (>2-5cm) GND wire from the probe kit?
Where did you connect the GND of the probe?
How did you connect the GND of the probe?
Did you use a short connection like the one in the picture or did you use the long (>2-5cm) GND wire from the probe kit?
I will try a shorter ground for the probe ( ground is take 1 cm away from the chip with 7 cm soldered wire ) , it was in x10 ,will try 100 nf cap for decoupling too
@ JensH , any suggestion for an better receiver ?
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@ JensH , any suggestion for an better receiver ?
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No, not a specific type. You should probably try with decoupling first. It might work OK. I have seen the TI DS90LV012A used for a similar application, but I think it is probably similar to what you use already.