Local oscillator for 22 GHz mixer

[Aalda]

Hi,
what solution use for LO at 22 GHz for upconverting OFDM signal (2,4 GHz 802.11n)? Is it possible to use Hittite chips (VCO + PLL) or DRO + PLL or something else?

Thank's

 

[tony_lth]

What is the modulation scheme for your OFDM signal?

 

[AMSA84]

What about DRO and a Gunn diode? Is the simplest way to do an oscilator.

Best regards,
Charles

 

[Aalda]

What is the modulation scheme for your OFDM signal?

standart wifi 802.11n
20 or 40 MHz channel bandwidth
56 or 114 subcarriers
0,3125 MHz spacing
64 QAM

What about DRO and a Gunn diode? Is the simplest way to do an oscilator.

Best regards,
Charles

do you have any reference or link?

 

[kh4n]

you can use hmc738 vco from hittite and a pll from adi or hittite. you probably wont need any opamp for the loop filter.
or use hmc833 or adf4350 generate 5.5ghz and multiply that with a multiplier to obtain 22ghz
but these are not cheap approaches.
PN might not depress you due to the 312.5khz carrier spacing

 

[biff44]

You are asking the wrong question. The question you might want to ask is: what phase noise do I require from my OFDM system. OFDM requires good phase noise to prevent intersymbol interference, so if the oscillator (upconverting LO on transmit side AND downconverting LO on receive side) have to be pretty good. As a minimum, they will need to be phase locked.

This paper suggests -105 dBc/Hz at 10 KHz offset, but your system needs may vary from it:


htpp://home.mit.bme.hu/~kollar/papers/Robertson.pdf

Once you know your phase noise requirements at 100 hz, 1 khz, 10 khz, 100 khz, 1 mhz....then you can read data sheets of phase locked oscillators and figure out if the will work. At lower frequencies a phase locked DRO will do fine, but by the time you get to 22 GHz, it may be all pooped out unless you get a good one.

 

[AMSA84]

Hello there,

Right now I can't tell you, maybe later.

BTW, for you to design a Gunn Oscillator based on a DRO you'll have to know how to work with: Smith Chart, Matching networks, Micro-strip lines.

 

[tony_lth]

The OFDM signal is BB modulation signal, so its phase noise is different from the 22G LO phase noise.
I had done the 22G LO signal for 128QAM, and had used the Hittite VCO even for 256QAM. But maybe the baseband is not OFDM, you can search microwave point to point telecommunications products for clues.

 

[Aalda]

I'll try Hittite's chips in configuration for direct mixer and for subharmonic mixer and I choose better solution