Hi All, I'm having trouble making an analog conversion of OFDM signal using DAC 904E from Burr Brown. The DAC works fine, I have set up a digital sine signal and when I looked at the osciloscope and spectrum analyzer it has 600mVpp and 0dBm power with good spurious performance in the baseband bandwidth that I want to use for OFDM (0-4MHz -- OFDM bandwith is 7MHz) with adequate sampling rate in 80MHz. But when I try to apply digital OFDM data into the DAC, the peak-to-peak voltage cannot reach 600mVpp and the power level is also lower. In fact, the peak-to-peak voltage is only 52mV and the power level is roughly -40dBm. I have make sure that the digital signal utilize full bit precission of the DAC. What happen here? Please help. thank you.
DAC Output Level in OFDM Signal
Started by ●February 18, 2009
Reply by ●February 18, 20092009-02-18
On Feb 18, 7:03�am, "gendruwo" <gendr...@ftml.net> wrote:> Hi All, > > I'm having trouble making an analog conversion of OFDM signal using DAC > 904E from Burr Brown. The DAC works fine, I have set up a digital sine > signal and when I looked at the osciloscope and spectrum analyzer it has > 600mVpp and 0dBm power with good spurious performance in the baseband > bandwidth that I want to use for OFDM (0-4MHz -- OFDM bandwith is 7MHz) > with adequate sampling rate in 80MHz. > > But when I try to apply digital OFDM data into the DAC, the peak-to-peak > voltage cannot reach 600mVpp and the power level is also lower. In fact, > the peak-to-peak voltage is only 52mV and the power level is roughly > -40dBm. I have make sure that the digital signal utilize full bit > precission of the DAC. > > What happen here? Please help. thank you.Do you know the PAR of your OFDM signal compared to a sine? How often does the PEAK occur in the OFDM signal? Mark
Reply by ●February 19, 20092009-02-19
<makolber@yahoo.com> wrote:>On Feb 18, 7:03�am, "gendruwo" <gendr...@ftml.net> wrote:>> I'm having trouble making an analog conversion of OFDM signal using DAC >> 904E from Burr Brown. The DAC works fine, I have set up a digital sine >> signal and when I looked at the osciloscope and spectrum analyzer it has >> 600mVpp and 0dBm power with good spurious performance in the baseband >> bandwidth that I want to use for OFDM (0-4MHz -- OFDM bandwith is 7MHz) >> with adequate sampling rate in 80MHz. >> >> But when I try to apply digital OFDM data into the DAC, the peak-to-peak >> voltage cannot reach 600mVpp and the power level is also lower. In fact, >> the peak-to-peak voltage is only 52mV and the power level is roughly >> -40dBm. I have make sure that the digital signal utilize full bit >> precission of the DAC.>> What happen here? Please help. thank you.>Do you know the PAR of your OFDM signal compared to a sine? > >How often does the PEAK occur in the OFDM signal?If I had to guess "what happened here", I'd guess that some designer on the project other than the OP decided the OFDM signal needed 40 dB of headroom. In almost all OFDM cases that would be more than the optimal amount of headroom, but the optimal amount depends upon more facts than are presented here. Steve
