about demodulator wave ???

[super]

Dear all :
The waveform is I simulation demodulator result.
But someone told me this waveform is not correct.
I don't know why ? What is ideal waveform ?
(The input is random data not regulator 1,0,1,0....)
So somebody can tell me why ??

Thanks ....

 

[Mazz]

Some more details are needed, for example the kind of modulation, and so on.
It seems to be the output of a GMSK demodulator for a system like DECT or Bluetooth with a pseudorandom sequence applied.
if so, the only problem I see is in the average of the curve at the beginning, this can make some mistakes (usually these systems has guard time and known initial preamble and sequences to get rid of it) and maybe the bandwidth of the filter is too low (sequences like 1010 are too low in amplitude, while 11001100 are ok).
But I have gone too far maybe...

I hope it can help.
Mazz

 

[wpsch]

Besides the curve at the beginning, the signal itself don't have constant average value. It is not suitable to use this slicer circuit. Imagine after a long '0' or a long '1', the output of the RC low-pass filter will becomes too low or too high to slice the coming signal. e.g. 0000.....000000101010... Add a switch between the RC filter and the demodulated signal. Close it during preamble and open it after. Or use some other modulation with constant average value.
Sorry, not exactly answer your question...

 

[super]

The circuit is 2FSK demodulator
data rate=6.6kbps , shallenkey filter=2 order (corner=3.5k)
RC loop filter =101Hz (input to slicer to get DC)

The input signal worst case only have 2 sequence "1" or 1 sequence "0",
so it won't have long "1" or long "0" case.
I had send 6 preamble (101010) then sequences random bit data.

Is the some of slicer input amplitude can't reach maxium amplitude
or DC problem not settling or BW too slow ?
because I see amplitude some are large and some are small .

Thanks .