Continue to Site

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.

Mixer input impedance matching

Status
Not open for further replies.

Fikadu

Junior Member level 3
Joined
Feb 22, 2015
Messages
31
Helped
0
Reputation
0
Reaction score
0
Trophy points
6
Activity points
304
Hello every one,

I am trying to use ad831 RF mixer. As it is stated in the datasheet, R||C input impedance matching is suggested by showing R and C values graphical for different frequencies. My problem here is, a unit for C values is not shown there. is it in pF, uF,nF? I have attached a screenshot of the graph in the datasheet. is there any one who may understand what is unit for the C values?

Thank you very much

C_Values.JPG


Datasheet Link: https://www.analog.com/media/en/technical-documentation/data-sheets/AD831.pdf
 

Hi,

You may easily find out in your own.

Simple calculations you can do:
"3" is from the table, "150MHz" is from the table. (Somewhere in the center of the table)

3uF --> xc = 1 / ( 2 × Pi × f × c) = 1 / ( 2 × 3.14 × 150 MHz × 3uF) = 0.00035Ohms
--> 0.35m Ohms will completely short your input signal to almost zero. It is far away from 50Ohms range.
So, "3uF" can not be the correct answer.
--> You may now try with nF and pF on your own.

Also the input capacitance is given in the specification table. With units.

Klaus
 

Can Input Impedance be in uF or nF range for an RFIC ?? Answer is simple, never...
So, it will logically be pF range..
 

Klaus, thank you very much for the response.

But, still I am a little confused. The first thing is that you calculate just for C, where as we are using R and C, not only C to make 50Ohms impedance range as it is shown in datasheet. Does that work?

The second thing is, as I was trying to understand by looking in to some other applications, the input impedance should not necessarily be 50Ohms. would you correct me if I am wrong here? would you look in to the following Link? **broken link removed**

While taking frequency, capacitance and Resistance at arbitrary point in the table and calculate impedance, it doesn't make 50Ohms too.


At last, you mentioned that the input capacitance is given in the specification table with units in the datasheet. I couldn't find that one. which table you mean?

Thank you a lot

- - - Updated - - -

Can Input Impedance be in uF or nF range for an RFIC ?? Answer is simple, never...
So, it will logically be pF range..

BigbBoss,
Thank you very much for your support.
I have still doubts that I have replied to Klaus above. would you refer it back ?

Thank you a lot once again
 

BigbBoss,
Thank you very much for your support.
I have still doubts that I have replied to Klaus above. would you refer it back ?
Thank you a lot once again
Either you calculate or not, nF or uF range of capacitors are not possible by its nature..
 

Hi,

Read your post #1.
Where is the question about "R"?
The values of R with units are given in the diagram.

My post refers to this question of post #1
what is unit for the C values?

Klaus
 

Status
Not open for further replies.

Similar threads

Part and Inventory Search

Welcome to EDABoard.com

Sponsor

Back
Top