Triad RF Systems
Windfreak Technologies
 

About RF Cafe

Kirt Blattenberger - RF Cafe Webmaster

Copyright: 1996 - 2024
Webmaster:
    Kirt Blattenberger,

    BSEE - KB3UON

RF Cafe began life in 1996 as "RF Tools" in an AOL screen name web space totaling 2 MB. Its primary purpose was to provide me with ready access to commonly needed formulas and reference material while performing my work as an RF system and circuit design engineer. The World Wide Web (Internet) was largely an unknown entity at the time and bandwidth was a scarce commodity. Dial-up modems blazed along at 14.4 kbps while tying up your telephone line, and a nice lady's voice announced "You've Got Mail" when a new message arrived...

All trademarks, copyrights, patents, and other rights of ownership to images and text used on the RF Cafe website are hereby acknowledged.

My Hobby Website:

AirplanesAndRockets.com

Electronics World articles Popular Electronics articles QST articles Radio & TV News articles Radio-Craft articles Radio-Electronics articles Short Wave Craft articles Wireless World articles Google Search of RF Cafe website Sitemap Electronics Equations Mathematics Equations Equations physics Manufacturers & distributors Engineer Jobs LinkedIn Crosswords Engineering Humor Kirt's Cogitations RF Engineering Quizzes Notable Quotes App Notes Calculators Education Engineering magazine articles Engineering software Engineering smorgasbord RF Cafe Archives RF Cascade Workbook 2018 RF Symbols for Visio - Word Advertising RF Cafe Homepage Thank you for visiting RF Cafe!
Exodus Advanced Communications Best in Class RF Amplifier SSPAs

Caps in IC design - RF Cafe Forums

RF Cafe Forums closed its virtual doors in 2012 mainly due to other social media platforms dominating public commenting venues. RF Cafe Forums began sometime around August of 2003 and was quite well-attended for many years. By 2010, Facebook and Twitter were overwhelmingly dominating online personal interaction, and RF Cafe Forums activity dropped off precipitously. If the folks at phpBB would release a version with integrated sign-in from the major social media platforms, I would resurrect the RF Cafe Forums, but until then it is probably not worth the effort. Regardless, there are still lots of great posts in the archive that ware worth looking at.

Below are the old forum threads, including responses to the original posts.

-- Amateur Radio
-- Anecdotes, Gripes & Humor
-- Antennas
-- CAE, CAD, & Software
-- Circuits & Components
-- Employment & Interviews
-- Miscellany
-- Swap Shop
-- Systems
-- Test & Measurement
-- Webmaster

marko
Post subject: Caps in IC design Posted: Sun Feb 26, 2006 2:00 am

Lieutenant

Joined: Sun Feb 26, 2006 1:56 am
Posts: 3
hello....someone asked me this question and i wasn't sure about the answer. for a dc block why not pick the smallest possible capacitance value because at dc no matter what the value is the cap will be an open. the only answer i could think of was that if you pick a very small cap value and depending on your frequency of operation you have unwanted ac voltage drop across the blocking cap because small cap. value will give rise to higher impedance. is there any other reason?

marko


Top

IR
Post subject: Posted: Sun Feb 26, 2006 3:05 am

Site Admin


Joined: Mon Jun 27, 2005 2:02 pm
Posts: 373
Location: Germany
Hello marko,

For DC block capacitors, the desired thing would be a low insertion loss for the AC signal. Therefore if you will choose the lowest possible value you will get the exact opposite.

The reactance value is given by:

Xc=1/(2*pi*f*C)

For most applications a reasonable value of reactacne is between 3 to 5 ohms. When you choose the capacitor value, it is of course most important to consider the frequency of operation, ESR and the SRF of the capacitor. You should be below the SRF of the capacitor, or else the capacitor might act as inductor.

There are many technologies of capacitors: Y5V, X7R... They differ from each other by temperature range, ESR value, SRF etc.

_________________
Best regards,

- IR


Top

marko
Post subject: Now, about inductorPosted: Sun Feb 26, 2006 4:26 pm

Lieutenant

Joined: Sun Feb 26, 2006 1:56 am
Posts: 3
thanks IR for your reply....one more question about passives in IC design. i know the definition of Q in English but don't completely understand the concept, especially this point: lower Q means more lossy inductor--does this mean that if you have a very low Q then the current entering one port of inductor won't equal current at the output because the lower Q means higher resistance and capacitive coupling to substrate (current going into the substrate)? is that essence of Q: that there would loss of current?

marko


Top

IR
Post subject: Posted: Sun Feb 26, 2006 4:41 pm

Site Admin


Joined: Mon Jun 27, 2005 2:02 pm
Posts: 373
Location: Germany
Hello marko,

Just a quick overview about Q Quality Factor:

There are 2 definitions:

1. Q defined as the ratio between the energy dissipated as heat to the total energy stored in the sine wave.

2. The more modern definition, which is valid for band-pass and band-stop filters:

Q=Fo/BW

The first definition is more of the unloaded Q and can be used to answer your question:

Very low Q means that the ratio of the energy being transferred through the inductor to the energy being dissipated as heat in the inductor is high. That menas that the inductor dissipates the AC energy in the form of heat due to the internal DC resistrance of the wire.

Q=Xl/Rdc

If Rdc (DC resistance) is high then Q is low. The same applies for capacitors only, instead of Rdc there is ESR.

_________________
Best regards,

- IR


Top

marko
Post subject: Posted: Sun Feb 26, 2006 5:53 pm

Lieutenant

Joined: Sun Feb 26, 2006 1:56 am
Posts: 3
hi IR...sorry i'm bugging you...so would you say there's loss of current? i mean the heat dissipated has to be because current is turned into heat from the series resistance and hence there will loss of current...is that right?


Top

IR
Post subject: Posted: Mon Feb 27, 2006 4:03 pm

Site Admin


Joined: Mon Jun 27, 2005 2:02 pm
Posts: 373
Location: Germany
Hello marko,

There is no such thing loss of current. There is loss of Enrgy and power. Energy is being dissipated in the coil because of its associated Rdc.

By adding this resistance ot the circuit, the current through the circuit is being reduced. If the Q is high, then the power dissipation through the coil will be reduced and more current will flow through it.

_________________
Best regards,

- IR



Posted  11/12/2012
Copper Mountain Technologies - RF Cafe
ConductRF Phased Matched RF Cables - RF Cafe
LOTUS Communications Systems Modular RF Component Building Blocks - RF Cafe
 

Please Support RF Cafe by purchasing my  ridiculously low−priced products, all of which I created.

These Are Available for Free