Welcome to EDAboard.com

Welcome to our site! EDAboard.com is an international Electronic 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 delay time in cubic predistortion?

Status
Not open for further replies.

daoyuan

Junior Member level 1
Joined
Dec 21, 2005
Messages
15
Helped
0
Reputation
0
Reaction score
0
Trophy points
1,281
Activity points
1,388
in Cubic Predistortion


delay can BE how compute
 

biff44

Advanced Member level 5
Joined
Dec 24, 2004
Messages
4,872
Helped
1,357
Reputation
2,710
Reaction score
1,038
Trophy points
1,393
Location
New England, USA
Activity points
36,704
Re: Predistortion Amp

Depends on the method used. If you are generating a distorting signal and adding it linearly to the main signal before transmit amplifier, you are adding delay so that the distorting signal vector is 180 degrees out of phase over a wide frequency range with the amplifier generated distorting signal. If it were narrowband modulation, you could get away with just a phase shifter to perform the cancelation. With wideband modulation, a phase shifter would not be able to cancel out all of the distortion frequency components simultaneously, so you generate the phase shift with a time delay.
 

daoyuan

Junior Member level 1
Joined
Dec 21, 2005
Messages
15
Helped
0
Reputation
0
Reaction score
0
Trophy points
1,281
Activity points
1,388
Predistortion Amp

"If it were narrowband modulation, you could get away with just a phase shifter to perform the cancelation. "

HOW to calculate the Delay Time
and HOW to realize ?
 

biff44

Advanced Member level 5
Joined
Dec 24, 2004
Messages
4,872
Helped
1,357
Reputation
2,710
Reaction score
1,038
Trophy points
1,393
Location
New England, USA
Activity points
36,704
Re: Predistortion Amp

Well, If I were doing it I would build a circuit with two connectors for attaching a coaxial delay line to, and in the lab I would input my modulation to the predistorter, pass the resulting signal thru the transmitter, and look at 2tone 3rd order products on a spectrum analyzer. I would then tweek the delay line length until they were nulled over the biggest portion of their bandwidth.

In practical circuits, you would probably have both amplitude, phase, and delay line lengths to fool around width until you got it right.

If you want to calculate such a thing, you would need a non-linear simulation program that could simulate both the predistorter and transmit amplifier non-linearities accurately, and you would do the same as above.

If you are up on FFT processing in something like Mathcad or Matlab, you could simulate it all to a first order there, modeling the predistorter like a nonlinear diode I-V curve, etc. Would not be very accurate though.
 

Status
Not open for further replies.

Part and Inventory Search

Welcome to EDABoard.com

Sponsor

Top