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.

Why not use square wave but sine wave as LO signal??

Status
Not open for further replies.

zhangjavier

Advanced Member level 4
Joined
Jan 10, 2005
Messages
102
Helped
0
Reputation
0
Reaction score
0
Trophy points
1,296
Activity points
757
a ideal switch operation can be get if a square LO is applied to the switching quad in a mixer. But conventionally we use a sine LO . Why?? Is it difficult to generate a high frequency square wave??
 

ahmad_abdulghany

Advanced Member level 4
Joined
Apr 12, 2005
Messages
1,206
Helped
102
Reputation
206
Reaction score
21
Trophy points
1,318
Location
San Jose, California, USA
Activity points
11,769
No, it's not difficult, but the local oscillator output is also used to be multiplied by other signals, and if it's square instad of sinusoidal, it would have different harmonics at output which will be much difficult to filter out...

I hope that this helps,
Ahmad,
 

safwatonline

Advanced Member level 4
Joined
Nov 19, 2005
Messages
1,341
Helped
219
Reputation
438
Reaction score
48
Trophy points
1,328
Location
EGYPT
Activity points
9,038
i think using square wave is the ideal case and i don't see any disadvantages in it except that it needs a Buffer from the VCO
 

flatulent

Advanced Member level 5
Joined
Jul 19, 2002
Messages
4,626
Helped
489
Reputation
980
Reaction score
150
Trophy points
1,343
Location
Middle Earth
Activity points
46,689
The problem is generating the square wave. At microwave frequencies it takes more resources (chip area, current drain, $) to make a square wave.

Overdriving the LO port of the mixer is almost as good.
 

BigBoss

Advanced Member level 5
Joined
Nov 17, 2001
Messages
5,368
Helped
1,553
Reputation
3,108
Reaction score
1,428
Trophy points
1,393
Location
Turkiye
Activity points
32,355
To get square wave, we use dividers to drive mixers. But in this case LO has to have 2X of frequency of operation.The main advantage of having square wave is to prevent 2nd harmonics and lower transient noise..
 

usrocky

Newbie level 6
Joined
Nov 13, 2006
Messages
11
Helped
0
Reputation
0
Reaction score
0
Trophy points
1,281
Activity points
1,339
how about the power of the signal?
 

estradasphere

Member level 4
Joined
May 17, 2005
Messages
78
Helped
4
Reputation
8
Reaction score
2
Trophy points
1,288
Activity points
1,900
as also flatulent said, the LO stage is not intensionally switched on/off with a sine wave. it is just difficult to obtain a square wave at high frequencies. you may use a buffer at the input of your LO port to switch your LO as abrupt as possible, but depending on your operating frequency, you'll never get a square wave as you'll always have a low pass effect due to the parasitics etc.
 

Status
Not open for further replies.

Part and Inventory Search

Welcome to EDABoard.com

Sponsor

Top