Question
I use the 10MHz reference source with R-counter set as 1. The output from the
VCO is at 2.38GHz. The prescalar is set as 8/9 using the AD evaluation software.
I have measured without any component hanging on MUXOUT. The measured voltage
level for N-counter is only about 1V at the 10MHz locked frequency, while for
the R-counter, it is around 3V. The same amplitudes are also observed using
ADF4107.
I have also tried using the ADF4157. Same phenomenon is observed for the
N-counter voltage also, around 1V at MUXOUT. There is no such phenomenon from
the N-divider/2, R-divider nor R-divider/2 outputs. All the voltage measured
are around 3V.
Is there any possible reason for the low amplitude for N-counter?
Answer
I checked both ADF4106 and ADF4157 Muxout. The level of N-divider output was
the same. There is a difference of duty cycle between N-divider output and
R-divider output.
For R-divider output (and N divide by 2) duty cycle is 50%, for N divider
output it's much smaller - around 10%. That doesn't matter on our eval board
without any components on Muxout.
for this case,it was resolved by changing a high bandwidth oscilloscope to
measure the N counter output.