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.

Connecting balanced LO input to balanced PLL output

Status
Not open for further replies.

richas

Junior Member level 3
Joined
Jul 1, 2011
Messages
25
Helped
4
Reputation
8
Reaction score
4
Trophy points
1,283
Activity points
1,464
Hi All,
This is a newbie question I suppose. I am clocking the LO of a receiver IC with an external PLL clock generator. Both the LO input and PLL output are balanced. Can I connect the directly with decoupling capacitors?

I understand the use of a balun to convert from balanced to unbalanced but is it also used to connect balanced ports?

Thank

Rich
 

RCinFLA

Advanced Member level 2
Joined
Aug 31, 2010
Messages
605
Helped
187
Reputation
378
Reaction score
189
Trophy points
1,323
Activity points
5,791
Re: Balanced to Balanced

If inputs and outputs are both true differential drive and have compatible common mode voltage range you may not even require coupling caps.

Sometimes the outputs require D.C. supplies so a centertapped transformer is used, or two coils and coupling caps, to feed D.C. to open drain or open collector outputs.
 
  • Like
Reactions: richas

    richas

    Points: 2
    Helpful Answer Positive Rating

richas

Junior Member level 3
Joined
Jul 1, 2011
Messages
25
Helped
4
Reputation
8
Reaction score
4
Trophy points
1,283
Activity points
1,464
Re: Balanced to Balanced

Here is the input circuit from an evaluation board for this receiver, it is what I find confusing. It appears to accept a balanced LO signal and run it through a 50:50 balun to a balance input. I am not sure why.

Thanks again.

Rich


rx_input.JPG
 

BigBoss

Advanced Member level 5
Joined
Nov 17, 2001
Messages
5,364
Helped
1,553
Reputation
3,108
Reaction score
1,428
Trophy points
1,393
Location
Turkiye
Activity points
32,336
Re: Balanced to Balanced

Here is the input circuit from an evaluation board for this receiver, it is what I find confusing. It appears to accept a balanced LO signal and run it through a 50:50 balun to a balance input. I am not sure why.

Thanks again.

Rich


View attachment 58151

It's not a balanced input, unbalanced input to drive your circuit externally.
Signal generators supply generally unbalanced signals and your circuit needs a balanced input clock signal and therefore they have put a balun transformer between balanced pins and clock input.
And some matching circuit...
 

RCinFLA

Advanced Member level 2
Joined
Aug 31, 2010
Messages
605
Helped
187
Reputation
378
Reaction score
189
Trophy points
1,323
Activity points
5,791
Re: Balanced to Balanced

The circuit appears to be an application test fixture board that allows a single ended input (through coax connector symbol) or balanced input (through two test points). It would not be necessary in your actual circuit if you have a balance LO output drive.
 
  • Like
Reactions: richas

    richas

    Points: 2
    Helpful Answer Positive Rating

biff44

Advanced Member level 5
Joined
Dec 24, 2004
Messages
4,981
Helped
1,372
Reputation
2,740
Reaction score
1,042
Trophy points
1,393
Location
New England, USA
Activity points
37,501
Re: Balanced to Balanced

It looks like you can do it, but unless you can find info on both data sheets to say they can be dc connected, I would definately leave in the two series caps c20 and c24. You can throw away that transformer mess.
 
  • Like
Reactions: richas

    richas

    Points: 2
    Helpful Answer Positive Rating

vfone

Advanced Member level 5
Joined
Oct 10, 2001
Messages
5,446
Helped
1,571
Reputation
3,145
Reaction score
1,180
Trophy points
1,393
Activity points
34,590
Re: Balanced to Balanced

...the transformer and C19...
 

richas

Junior Member level 3
Joined
Jul 1, 2011
Messages
25
Helped
4
Reputation
8
Reaction score
4
Trophy points
1,283
Activity points
1,464
That makes sense. Because it is a schematic from a development board there is a lot of extra circuitry there to confuse this newbie.

Thank you
 

Status
Not open for further replies.

Part and Inventory Search

Welcome to EDABoard.com

Sponsor

Top