aaron_do wrote on Jan 19th, 2010, 11:27pm:1) Am i right in using an MSK signal to represent the half-sine pulse shaped OQPSK signal of the IEEE 802.15.4 standard?
Strictly speaking, they are different.
But for ACPR evaluation purpose, you can use MSK signal as substitution for half-sine pulse shaped OQPSK.
aaron_do wrote on Jan 19th, 2010, 11:27pm:2) How much time resolution should I use for the vpwlf file?
I use tstep=(1/Rsymb)/16 for Isig and Qsig files, here Rsymb=2Msymbol/sec.
Actually I use these files for generation of half-sine pulse shaped OQPSK by using actual vector signal generator, Agilent E4438C.
So my files for "vpwlf" are provided as tstep=(1/Rsymb)/16.
In Envelope Analysis of Cadence Spectre, first I set "envmaxstep=(1.0/2M)/16". But this setting resulted in simulation failure.
Next I set "envmaxstep=(1.0/2M)/32", this setting can finish simulation without failure. But there are still unreasonable bumps in envelope.
If I don't set "envmaxstep", simulation results in failure after very short time.
In Envelope Analysis of Agilent GoldenGate, I set Tstep=(1.0/2M)/256, because Envelope Analysis of Agilent GoldenGate is fixed time step analysis. So noise bandwidth is 512MHz.
aaron_do wrote on Jan 19th, 2010, 11:27pm:3) I need to lpf the vco output in order to remove the high orer harmonics of the carrier.
So I figured I could use a butterworth filter from the rfLib with a cutoff around 2.5 GHz and about 5th order.
Does that sound ok?
As far as LPF doesn't cause group delay distortion inside modulation bandwidth, it is ok.
But since you use behavioral VCO, so I think higher hamonics are never generated from VCO.
See the followings. Here I use I/Q-Modulator for generation of MSK or half-sine pulse shaped OQPSK.
http://www.designers-guide.org/Forum/YaBB.pl?num=1195226387http://www.designers-guide.org/Forum/YaBB.pl?num=1262000981http://www.designers-guide.org/Forum/YaBB.pl?num=1260978648http://www.designers-guide.org/Forum/YaBB.pl?num=1262828862/29#29