Anatech Electronics (RF Filters) - RF Cafe
Berkeley Nucleonics Academy RF Boot Camp - RF Cafe
 

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!
everythingRF RF & Microwave Parts Database (h2) - RF Cafe

small-signal, large-signal - 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

shane
Post subject: small-signal, large-signal Posted: Wed Oct 05, 2005 2:16 pm
hi guys,

i'm a sophomore undergrad. and i've a question to ask. what's meant by small-signal and large-signal. small-signal means ac signal with small amplitude? and large-signal means ac signal with large amplitudes? this is what i thought but in a book it says 'large-signal or dc'...now i'm confused. also, is small/large signal referring to the Amplitude or Frequency? please respond....thanx

shane


Top

Guest
Post subject: Small-signal vs. Large-signalPosted: Wed Oct 05, 2005 3:13 pm
Small-signal means "small enough that the performance of the circuit doesn't depend on the amplitude of an AC signal". In other words, the circuit is essentially linear - no AC voltages are large enough to change the operating conditions.

Large-signal means "big enough that the performance of the circuit depends on the the signal amplitude". There may be harmonics or intermodulation products, a change in bias conditions, or increased power consumption.

In RF, we generally are not interested in DC amplifiers. But if we are, the definitions above still hold - if the circuit is linear, it's small signal.

Good Luck!


Top

shane
Post subject: Posted: Fri Oct 07, 2005 1:54 am
thanx...your explanation helped but still begs the questions: why large signal is same as dc. as i said earlier, a book says "....large signal or dc'...why? thanks


Top

Guest
Post subject: Small-signal/Large-SignalPosted: Fri Oct 07, 2005 7:22 pm
My previous reply was from an RF point of view. For any number of reasons, RF circuitry is almost always AC coupled - thus eliminating any question of a "DC signal". (In a previous job, one boss's definition of "DC" was "any frequency under 30 MHz". That may be a bit extreme...)

There are cases where response down to DC is needed. In this case, it's possible for either the AC signal or the DC baseline (it's still hard for me to talk about a "DC signal") to change the operating point of the circuit.

Consider an opamp output circuit with a class AB output stage, driving a small-ish load resistance, from a balanced positive and negative supply. When the output signal is centered (near ground), both output devices are carrying current. That current is the quiescent or resting current. A small deviation, AC or DC, won't change the fact that both output devices are active, and current now flows in three devices: the pull-up transistor, the pull-down transistor, and the load resistor.

Now if the input raises the output voltage enough, whether temporarily or permanently ("AC" or "DC", respectively), the pull-down transistor turns off. (That's what class AB is, after all - less than 360 degree conduction but more than 180 degrees). Now the operating point has changed, and the term "large signal" applies.

Clear yet?

Good Luck!



Posted  11/12/2012
high frequency PCB of PCBONLINE
EMC Directory
Amplifier Solutions Corporation (ASC) - RF Cafe
 

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

These Are Available for Free