Use Of PLL for c and X band Signal generation.

[deepu.deep2112]

Dear All,

I am in process of designing a Local Oscillator Module which will be capable of generating c and X band signal ( 7400 MHz to 8100 MHz). I have initiated the design with a bought out 60 MHz source for my source signal generation.but converting 60 MHz into 7400 MHz to 8100 MHz,multiplication factor is so much.Mean i need to multiply almost 130 times,which is increasing the circuit complexity due to filtering and amplificatiom. Alternate approach I am thinking for generating high frequency signal through PLL and them multipling it. Is there any disadvantage I go through PLL? How much max signal I can generate from a single PLL device? Kindly guide me.

Thanks for Co-operation.

 

[afz23]

You can have a reference source at higher frequency,this will reduce N.But if you
want to use low freq reference,,then PLL is a good option for higher order N.
You can generate X-band or higher,provided you have a VCO in that
at range.Some synthesizer chips may not support RF feedback at X-band,but
you can go for a prescalar in feedback path.

 

[biff44]

I would buy a HMC764LP6CE from Hittite, hook up a 50 MHz reference oscillator to it, and call it a day.

 

[kh4n]

I would buy a HMC764LP6CE from Hittite, hook up a 50 MHz reference oscillator to it, and call it a day.

exactly !

 

[deepu.deep2112]

Kindly let me knw about the phase noise of PLL devices.As I have heard that phase noise of PLL devices is observed to be poor...i.e. in the range of 100 dBc/Hz @100Hz offset. Is it so?

 

[kh4n]

if we consider the whole frequency generation loop, PN depends on many factors such as ref clk you use, your loop filter BW, your VCO and PLL.
If you check the datasheet of HMC764LP6CE, the part biff44 suggested, its PN at 100k offset is around 120dBc/Hz. You can improve it with a better reference like an OCXO or even better depending on your budget. But the main question is, do you really need much better phase noise than 100dBc/Hz @ 100K
You can check `dean`s book` for pll basics.

 

[deepu.deep2112]

Actually I need max of -125dBc/Hz @100Hz offset not even 100KHz.
Spec for the generated LO signal around 8GHz is -80dBc/Hz @ 100Hz offset.So for that I need a better phase noise of the source.Thatswhy I am nt able to decide whether I should go for PLL or oscillator.

 

[biff44]

Actually I need max of -125dBc/Hz @100Hz offset not even 100KHz.
Spec for the generated LO signal around 8GHz is -80dBc/Hz @ 100Hz offset.So for that I need a better phase noise of the source.Thatswhy I am nt able to decide whether I should go for PLL or oscillator.

Then I suggest you hire a smart consultant to design a custom one for you

 

[Bob60]

8GHz is -80dBc/Hz @ 100Hz

Oh that is walking area of the flicker noise. Right BJT references oscillators and so on.