High speed coupling capacitor

[Ipanema]

uf coupling capacitor

hi,

Need your advice in choosing capacitors for high speed application at 3.125Gbps.

1) AC coupling / DC blocking 1uF

2) Power supply decoupling 0.1uF and 0.22uF

Pls recommend any specific model/brand that can suit my application and may I know what specs to look for in this application?

Thank you and best regards,
Ipanema

 

[IanP]

high speed coupling

For these frequecies 1µF sounds like talking about DC.
You can obviously use µFs and nFs capacitors, but more effective would be to use pFs small in size ceramic capacitors, such as, for example, from MURATA: **broken link removed**
And I have here in mind both functions: AC coupling/DC blocking and De-coupling.
Regards,
IanP

 

[Ipanema]

capacitor for high speed ac coupling + cap type

Hi Ian,

thanks for your reply. My application need at least 0.1uF of ac coupling capacitor. Are there no high frequency capacacitor for this value?

What specification should I look at for high speed application?

Regards,
Ipanema

 

[moda]

Hello,
I did use normal, Yes, normal 100NF 0402 ceramic cap for 10Gb/s 50 ohm termination, no problems at all.
It did compare it with high Freq capacitors that cost $1 with no different in performance at all!

Regards

Moda

 

[Wenye]

Hi, Ipanema

You can use multi-layer ceramic capicitor. We use 0805 for cable tv application

It need flatness response from 5MHz to 1Ghz. I think it will not cause problems in your system.


Regards,

Wenye

 

[Ipanema]

Hi,

That's surpising. According to AVX application notes :

**broken link removed**

If the signal operating frequency is above the capacitor Serial resonance frequency, the capacitor will behave inductively, which it will performs as Low Pass filter and you won't get anything at the output. Pls advice. I just read this.

Regards,
Ipenema

Added after 1 minutes:

hi moda and Wenye,

Can you pls let me know which model/brand that you use?

Regards,
Ipenema

 

[nemoium]

hi , i'm also interested in this subject,
if you find an answer ,pls tell me .
thank u very much .
my email : 51@21cn.com

 

[flushrat]

https://www.pulseresearchlab.com/products/mini/index.html

I used the 0.1uf DC block. It's good for 3.125G or above.

 

[Ipanema]

Hi,

I would use this for prototype board. So pls suggest any solderable SMT type of AC coupling caps.

Hi Flushrat,

Thanks for your info. That would make a good reference coupling cap.

Regards,
Ipanema

 

[moda]

Hi again
I know the freq graphs of normal 100NF ceramic cap but:
I did some test with VERY sensitive circuits with jitter of 10Psec for 50 ohm application and to my surprise as well I didn't had any degradation in performance for a normal ceramic cap or high price good cap for 10Gbsec systems!!!
Just use normal any brand 100NF 0402 and it will work OK, no problems.

Regards

Moda

 

[songsong]

1uF DC blocking CAP at 3.125Gbps is too large, and I think 1pF is enough.

Power supply decoupling CAP can place many values CAP shunted.

 

[moda]

To - songsong,

Sorry, this one not going to work well. I did test it with small capcitors, without good results.

Regards

Moda

 

[batdin]

I don't see what the problem is.Why not connect in parallel two capacitors-one normal 0.1uf for lower frequencies and one ceramic 100pF for higher freq.

 

[moda]

You will creat stab...

10GHz its sub milimiter harmonic waveform. and the parasitic of one 100NF cap will do the the work for you.

Regards

Moda