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.

Register Log in

what happens to RF choke while doing ac analysis

Status
Not open for further replies.

circuitking

Full Member level 4
Joined
Jan 8, 2018
Messages
222
Helped
1
Reputation
2
Reaction score
1
Trophy points
18
Activity points
1,950
Hi, I know how to find dc analysis (to find gm) and ac analysis (to find gain) for a given circuit (Say CS stage) when resistive load (say R)is there, i.e. Resistor is connected between Vdd and drain terminal. From this I can arrive at the conclusion that voltage gain Av=-gm*(rds//R).

IMG_20190709_193700.jpg

But what happens if I have a RF choke conected between Vdd and drain terminal. While performing AC analysis inductor (RF choke) should become open circuit which leaves drain terminal to be open and then the calculated voltage gain Av=-gm*rds. Is this correct or should we take the impedance of RF choke and include it also in the calculations?.

I also heard from a friend that there is something called RF anlysis also just like DC and AC analysis. I am wondering what that might be, anyone has any idea about it
 

BigBoss

Advanced Member level 5
Joined
Nov 17, 2001
Messages
4,809
Helped
1,455
Reputation
2,908
Reaction score
1,309
Trophy points
1,393
Location
Turkey
Activity points
29,032
RF Choke will act as Open Circuit for AC Signals and Av=-gm*rds will be as you have remarked ( Open Circuit Voltage Gain ). Another advantage of using RFC is that'll give you more Voltage Headroom for Vds ( no voltage drop on it ).These are however valid for ;

*Reactance of the RFC is sufficiently high for lowest AC frequency
*Self Resonance has never been taken into account ( it ought to be in practice )

AC Signal Analysis is general purpose and it is used very rarely in RF designs. But s-parameters analysis and especially HB analysis are used essentially in RF Circuits.
 

circuitking

Full Member level 4
Joined
Jan 8, 2018
Messages
222
Helped
1
Reputation
2
Reaction score
1
Trophy points
18
Activity points
1,950
*Self Resonance has never been taken into account ( it ought to be in practice )
Could you explain more about this ? does this mean at the self-resonance frequency the RFC will have an internal resistor and I should take that into consideration?

- - - Updated - - -

AC Signal Analysis is general purpose and it is used very rarely in RF designs. But s-parameters analysis and especially HB analysis are used essentially in RF Circuits.
Is there a recommanded procedure to perform S-parameter analysis and HB analysis, just like AC and DC analysis, to understand easily for beginners? Any good book or tutorial?
 

BigBoss

Advanced Member level 5
Joined
Nov 17, 2001
Messages
4,809
Helped
1,455
Reputation
2,908
Reaction score
1,309
Trophy points
1,393
Location
Turkey
Activity points
29,032
-Self Resonance Frequency is the functional limit of the RFC so that RFC cannot be used beyond SFR due to changing behavior of its nature.( beyond SFR, the RFC is not Inductor anymore, instead it's a dominantly capacitor )
-For s-parameters analysis and HB analysis, see the Help of the simulator which you will choose and search internet because there are lots of docs.
 

biff44

Advanced Member level 5
Joined
Dec 24, 2004
Messages
4,831
Helped
1,354
Reputation
2,704
Reaction score
1,031
Trophy points
1,393
Location
New England, USA
Activity points
36,482
do you mean "RF CHOKE", which is an inductor that deliberately has high loss, and an "INDUCTOR", which deliberately has low loss (i.e. high Q)? Makes a big difference in the answer
 

kripacharya

Banned
Joined
Dec 28, 2012
Messages
1,209
Helped
182
Reputation
360
Reaction score
175
Trophy points
1,343
Location
New Delhi
Activity points
0
do you mean "RF CHOKE", which is an inductor that deliberately has high loss, and an "INDUCTOR", which deliberately has low loss (i.e. high Q)? Makes a big difference in the answer
I believe it means high impedance at high (relevant) frequencies. Whether by inductance or not.

Usually preferrable by inductance, since DC bias gets affected if it's due to resistance.

Having said that, I do not think an element designated as an RF choke needs to be designed with hi-Q. That's more relevant for tuned circuits and such applications.
 

Status
Not open for further replies.
Toggle Sidebar

Part and Inventory Search

Welcome to EDABoard.com

Sponsor

Top