What may be the problem?
时间：03-23
整理：3721RD
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Hi,
I have a PCB with RF and digital on same board. Currently I am just esting the RF. The digital is not populated. One of the outputs of the RF is a reference cloack output of 90MHz (at a low level). Whenever I amplify this and then use to drive a D flip flop there is an interence in the output. I do not know how this coupled.
1) The refernce to amplifier path is around 2cms
2) There is not interference without the D flip flop.
3) The interefence reduces by 8-10 dB after shielding, but we need a reduction of 45dB.
Any thoughts on this?
BRM
I have a PCB with RF and digital on same board. Currently I am just esting the RF. The digital is not populated. One of the outputs of the RF is a reference cloack output of 90MHz (at a low level). Whenever I amplify this and then use to drive a D flip flop there is an interence in the output. I do not know how this coupled.
1) The refernce to amplifier path is around 2cms
2) There is not interference without the D flip flop.
3) The interefence reduces by 8-10 dB after shielding, but we need a reduction of 45dB.
Any thoughts on this?
BRM
It is almost impossible to guess. I need to see schematic, pcb and captures with distorted signal (at least the significant portions). PM them to me if you can.
/pisoiu
D-Flip-flop is high input impedance device, and your amplifier is probably not well match to it, so it can oscilate when it is connected to the input. Your intereference can simply be oscilating of the amplifier.
I would simply try to terminate the amplifier output/oscilator input with 50 Ohm resistor.
Maybe it is Helpful
Regards
D.