Other Parts Discussed in Thread: LMV112
We are using AFE4490 IC in our design.We are facing difficulty in passing Radiated emission test.
We have three boards in the design. The Main board with processor , AFE board with two AFE4490 IC's and LED board . The AFE board is connected to processor board with a FPC flex cable.
In AFE baord ,we are using a single 8MHz Oscillator with a clock buffer LMV112 for feeding clock for both AFE's .
In Radiated emission test , we are seeing a pattern of narrow band emission repeating exactly at 8MHz . The unit emissions crossing the limit in the band 200MHz to 500MHz . We found that the problem area is AFE board by some experiments . The Processor board operating alone has no issues .
We observed improvement around 5dB when the LED board is disconnected from the AFE board . My questions are as follows
1) AFE board is realized with 2 layer PCB - Is this OK ?
2) We are connecting LED with common Anode push pull configuration , There is no Series resistor for LED . In this case do we need supply pin 17 and pin 18 with 5V ?
Please suggest any key hardware checks and software settings we need to do to reduce emissions from the board .
Let me know if you need more information.