We're using the LM567CM/NOPB tone decoder. I have implemented on the bench fine working at 295kHz but in application the output is extremely noisy. We have used this chip successfully at lower frequencies of 40-75kHz. It should be able to lock onto frequencies up to 500kHz.
I've attached a picture of what's happening. The output TD should be locking on to the VGA signal, especially during 1ms - ~1.4ms but it isn't. I have tried several configurations for the capacitors but without any luck. All application notes are for frequencies below the 50kHz range (all that I have found anyway). In order to keep R1 within 1-10k range, I had to decrease C1-C3 to below the typical values - I'm working in the low nF ranges.
Is there anything that should be considered when working at higher frequencies?
It is noted that at high frequencies to ensure you have able decoupling on the power supply and I do.
Other than that I can't find anything that indicates design considerations for high frequency application.
Please let me know if you have any information that may be helpful.
Thanks,
