Joined: 30 April 2008
Location: AT
Posts: 6
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Dear Melexis support team,
I think I found a quite important "error" in your EVB90121 layout: As I am using a "non"-Standard-antenna (but with Impedance matching to 50 Ohms) I had to use the external enevelope detector as described in your Application notes.
But then I found out that the voltage supply at pin VDD is quite noisy because there you use it as a common pin for the output stage, the digital section and the analog receiver section.
I did a few simulations with a "real" X7R-cap. and found out that due to its limited RF-ability a ripple voltage of appr. 50-100mV peak-peak cannot be suppressed in the actual layout.
If no separate decoupling of VDD occurs at the external envelope detector I found out that the ripple at the RX pin causes wrong "1"-signals at the DOUT pin.
I suggest to use the VK200 joke only to decouple the output stage and connect the other supply lines directly to the output of the voltage regulators; maybe separated by their own L-C-combination.
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