Welcome to EDAboard.com

Welcome to our site! EDAboard.com is an international Electronics Discussion Forum focused on EDA software, circuits, schematics, books, theory, papers, asic, pld, 8051, DSP, Network, RF, Analog Design, PCB, Service Manuals... and a whole lot more! To participate you need to register. Registration is free. Click here to register now.

How to calculate oversampling ratio in fractional n PLL?l

Status
Not open for further replies.

nani

Junior Member level 3
Joined
Mar 17, 2005
Messages
27
Helped
4
Reputation
8
Reaction score
3
Trophy points
1,283
Activity points
1,536
hi,
can any one give me the idea how to calculate oversampling ratio in fractional n pll.
 

rfsystem

Advanced Member level 3
Joined
Feb 25, 2002
Messages
914
Helped
149
Reputation
294
Reaction score
38
Trophy points
1,308
Location
Germany
Activity points
9,548
Re: fractional n pll

Oversampling does not apply to PLLs instead of A/D and D/A. There is only a factor between the loop bandwidth and the comparison frequency. This ratio is between 10 and some 1000.
 

nani

Junior Member level 3
Joined
Mar 17, 2005
Messages
27
Helped
4
Reputation
8
Reaction score
3
Trophy points
1,283
Activity points
1,536
Re: fractional n pll

hi,
rfdesign i feel u r right to certain extent,but what about fsk modulation using sigma delta fractional n freq synthesizer here we can apply the concept of oversampling.

as u said it may not be applicable when we r feeding a constant dc signal

thank u
 

pengboy

Member level 1
Joined
Jun 28, 2003
Messages
36
Helped
3
Reputation
6
Reaction score
0
Trophy points
1,286
Activity points
411
Re: fractional n pll

if you r saying about frequency modulated signal, it should be similiar to ADC.

first you should have base band signal (frequency changing with time) and the bandwidth for the baseband signal.

so the OSR is determined by signal to distortion ratio, the strucure of the sigma delta, and the baseband bandwith. even in ADC, for optimum performace, the OSR is also need to be optimized based on those .

it really needs simulation based on behaviral models to decide the OSR, the loop can be just simplified as a low pass filter following the sigma delta modulaor.

another thing is for Fractional-N, usually the crystal reference is used as the clock for the sigma delta modulator.
 

Status
Not open for further replies.

Similar threads

Part and Inventory Search

Welcome to EDABoard.com

Sponsor

Top