The RF Class C amplifier - basics and simulations (1/2)

#147 In this video I look at the basics behind the Class C amplifier. I have a look at how it works, how it behaves and what are some things to keep in mind when designing such a circuit. And to show things off, I also try to simulate the various behaviors and effects using LTspice.
Further reading:
Radio-Frequency electronics; J. Hagen; Cap 9.1
cdn.macom.com/datasheets/MRF3...
www.analog.com/en/technical-a...
Transistor spice model source:
www.centralsemi.com/docs/csm/...
Related videos:
Class A amplifier part 1 - • The Class A amplifier ...
Class A amplifier part 2 - • The Class A amplifier ...
Class B amplifier part 1 - • The Class B amplifier ...
Class B amplifier part 2a - • The Class B amplifier ...
Class B amplifier part 2b - • The Class B amplifier ...
Class C amplifier part 1 - • The RF Class C amplifi...
Class C amplifier part 2 - • The RF Class C amplifi...
Class D audio amplifier part 1 - • The Class D audio ampl...
Class D audio amplifier part 2 - • The Class D audio ampl...
Class D audio amplifier part 3 - • The Class D audio ampl...
Class D RF amplifier part 1 - • The Class D RF amplif...
Class D RF amplifier part 2 - • The Class D RF amplifi...
Impedance Matching (1/2): • Lossless Impedance Mat...
Impedance Matching (2/2): • Lossless Impedance Mat...
Special Thanks to all my supporters on Patreon! Especially @afiskon, Ralf B., Paul Pr. Richard and Jonathan Alvarado!
If you liked this video be sure to check out my other videos and you can also subscribe to be up to date with all the new ones!
If you want to support the creation of more and better videos please consider checking out: / feszelectronics

[@johnlegros1586]

absolutely great explanation of class C behavior , am an old retired RF engineer and used this in quartz LO multipliers and even in TV output power for narrow band ( ~10 MHz bw at 800 MHz freq ) , and with an SA could get very low 3rd and 2nd harmonics , but with very long and difficult time finding the correct impedance/Q matching elements using cavities and slit couplings ...had no such fabulous simulation tools at the time , mostly the nose , experience and lot of time ....very nice return in my past , Thanks !!

[@fifaham]

Excellent work - I studied RF circuit design about 20 years ago and I keep updating myself with presentations such as yours. Thank you for your support.

[@carmelpule8493]

Brilliant and superb presentation. This gentleman knows a transistor and the power transfer requirement, Unlike many other " electronics contributors, he did not just fill a whiteboard with his handwritten notes and spend the time reading it, wavering his pen on the written sheet, describing what the unit does rather than the detail of how it works. Thank you Sir, for respecting your audience and in turn you should be highly respected. Thank you once again. .

[@sinclair8811]

Nice work, man! I hope you'll continue the topic of RF circuits :)

[@acestudioscouk-Ace-G0ACE]

Agreed, we need more RF please!

[@paulp1204]

Great video, very nice overview of the class C, and several pro tips for LTSpice as well. Your impedance matching tutorial has come in handy already! I have an old 2 transistor FM radio microphone kit that uses this amplifier, so I'll dig it out and see how they configured it. Thanks for the inspiration Fesz.

[@FesZElectronics]

This type of amplifier is quite good for FM since the wave amplitude is always constant and the frequency varies only within the limits of the various LC resonators and components.

[@wgm-en2gx]

You explained this very well. I have a basic understanding mostly from digital electronics. However, I was able to follow this video quite well.

[@josephf6785]

I am not sure how I did not know of this channel until now, but you have some great content here! This explanation was really well done, and the simulations were really concise!

[@CodeJeffo]

Excellent explanation 👍

[@user-uk5ep9hm5k]

Excellent explanation!

[@olivierconet7995]

Super well explained, I finally understand how to play with class C !

[@rubenhidalgocarrillo]

Great material, as usually. Thanks for your videos.

[@alessiocaffi5992]

Just popped out in my recommended .Very interesting and nice review. Compliments!

[@robertfindley921]

Nice refresher! I like your transistor pendulum!

[@rjordans]

Excellent tutorial again, thanks!

[@cyberphox1]

Got to be one of the best electronics channels 💪

[@chandanchandu4126]

Excellent explanation!!

[@weinihao3632]

Superb explanation!

[@dmitry.shpakov]

The best explanation ever!

[@yasirshafiullah3016]

This is super good.. Thanks Alot for explaining.. This is very interesting with simulations!

[@__--JY-Moe--__]

nice follow through presentation!! congrat's!!

[@raphaelcoti692]

Always good videos !! Keep going on man !

[@elwood.downey]

Very clear, thank you.

[@granttaylor3697]

If you are interested I can provide you with information about switching amplifiers, as that has been my main area of research for the last four years and I have invented three new classes, O, P and Q. As each switching class as in linear types have a range of very useful applications in electronics, for both RF and AF designs.

[@dmyegorov74]

Great work ! Thank you !

[@redrostream2972]

love your smarts and info my friend **

[@hedleyfurio]

Excellent as always 👍

[@rudinei_do_conto]

Obrigado pelo ótimo conteúdo, excelente vídeo... Muito sucesso ao canal. Saudações do Brazil.

[@johnwest7993]

Thank you.

[@googlem7]

Excellent 👍

[@alaricsnellpym]

Awesome! Another useful one for the radio tinkerers out there :-)

[@PepeAlipido-ph9dz]

very very good

[@joejane9977]

A fricken PLUS PLUSS thanks that was wonderfull

[@aliptera]

A transistor pendulum! I didn't know such thing exists - LOL!

[@bsuryasaradhi6816]

Gold❤️

[@R2AUK]

Thanks for the video. I think it's simpler to think about class C PA in the frequency domain. The parallel LC circuit forms a band-pass filter. The class C PA works as a switch, thus generating multiple harmonics of the original signal. These harmonics can be filtered using a corresponding band-pass filter, which creates the "frequency multiplication" effect. The waveforms at 7:30 don't show that the frequency multiplier is unreliable, but that the band-pass filter is not great, thus there are other harmonics than the desired one in the output signal.

[@FesZElectronics]

I guess that what I meant by unreliable was that if you are trying to generate very large frequency multiples, at some point the input signal is not properly multiplied, but rather the output frequency depends more on the center frequencies of the various LC circuits than the input signal frequency.

[@R2AUK]

@@FesZElectronics I'm afraid that's not quite accurate either. The harmonics will be all over the spectrum. You just need a narrow band-pass filter to filter the right one, that's it. In practice, people don't use literally an LC circuit on the collector, because that's indeed not the greats filter. Usually, you will see a 1:4 transformer that converts 50 Ohm load to 200 Ohm one on the collector and a following 7-pole LPF/BPF, or maybe a crystal filter. You can find the concrete example in the schematic for video number 17 (page 9) on my channel, although I used a MOSFET instead of a NPN transistor.

[@01masuda]

I called Ic singal(with broken tip) Spork signal. When Ic becomes spork signal, 2nd 4th sprious increases. Then Conventional AM transmitters apply simultaneous modulation to the final stage and the excitation stage.

[@LightningHelix101]

Waiting for this classy class-C to live the ideal dream of conduction angle zero.

[@MegaCadr]

Yay RF amplifiers! Could you do switch mode RF amps in the future? Especially interested in using MOSFETs and the drivers at HF.

[@tahanprahara]

How to choose the right capasitor and inductor for the load example 50ohm antena? Thank you sir

[@vincei4252]

Excellent presentation and explanation of some small details the text books gloss over and leave you scratching your head. How good is LTSpice for simulations of these types of circuits for frequencies from 7-14 MHz? 20-40 meters ?

[@FesZElectronics]

In general the simulation result is only as good as the component models that you are using - if various parasitic elements are removed to get a simpler design, then the observed behaviors will differ from realty.

[@kocheltree]

Won't your blocking capacitor change the impedance that needs to be matched in going from the 500 ohms to the 50 ohms or is it a negligible value?

[@acestudioscouk-Ace-G0ACE]

Really interesting and useful, thank-you. Now I know what the Q factor is.... I used to think it was something to do with James Bond 007!

[@grigus1]

Thanks for another great video! I'm wondering, how a class-C amplifier behaves in spread-spectrum RF systems? Like Wifi, Bluetooth, etc

[@blockcamp]

WiFi and Bluetooth both require large bandwidths and that's not something class c can support.

[@geertas]

in many class C amplifier the Capacitor which is parallel with the coil on the collector is omitted. Can you explain why that is?

[@aitorsierra]

Hi @FesZ Electronics. In the case of 2.5v I have obtained different results with Eff2 and with the same values and the same circuit. Could it be something related to the numerical resolution of LTspice ?. Could you please share your LTspice file ?. Thanks

[@FesZElectronics]

Hello Aitor! One thing I think was not mentioned clearly in the video was that in the transient simulation setup, I set a stop time at 500us and a start time at 300us - the idea here being that I wanted to exclude any start-up behaviors. What exactly was the efficiency you obtained (and what was the reference in the video)? Another thing that might be different was the spice model used for the transistor - I will add it in the description. Regarding file sharing, I restrict this to certain tier of Patrons, in an effort to thank them for their contribution.

[@hanangonen8732]

Very good explanation ...as usual . Can you make a video about yourself ...knoledge resorces,education ...are you working as an hw engineer or electronics is just an hobby ...

[@stark9397]

Hİ, can you make a video about avalanche transistor or diode? Fmmt417 is a good avalanche transistor and it has .spice file but I can't use it in marx generator. Even though the transistor goes into avalanche mode, it turns off in a short time and I can't get the output voltage. Thank you for the videos and useful information :)

[@briant4326]

Really appreciate the fantastic video thank you. Just one basic thing I'm hung up on. I've read that sometimes LC circuits are used as filters. So they have infinite impedance (when parallel) at resonate frequencies. Does that not apply here? It doesn't seem that the transistor is operating as if it has infinite impedance in the collector. So i'm confused as far as when to treat it like a filter versus when to treat it like an oscillator. Anyways thank you.

[@FesZElectronics]

It does work as a filter here as well, its just that you need to consider that the LC is also in parallel with the load R; so at resonance, the equivalent impedance of the whole group (parallel RLC) is R (the LC is infinite as you mentioned); and at any other frequency the impedance is lower because of there reactive behavior of the LC group.

[@ltlt6117]

Hi i made a common emmiter amplifier for 200mhz signal with 2× gain I can amplify a 50 mv p-p to 100mv p-p but I can't do it for 2v to 4v p-p Why what values should be change???

[@panjisetyonugroho5219]

Can you teach us how to simulate input and output impedance of amplifier ?

[@fullwaverecked]

Nice video. At least five volts? Q factor recommended. What is the max Q for class C? Thanks! You have a new subscriber. Cheers from Utah!

[@FesZElectronics]

Q is dimensionless (its a Q of 5); or did the 5V refer to something else? I don't think there is theoretical limit to the Q value other than real life - very high Q means very little inductance and a large capacitance - you need very large current pulses to drive it; also components have tolerance - if you have a very large Q, you can simply miss the desired operating frequency under specific conditions (temperature for example will impact component values)

[@fullwaverecked]

@@FesZElectronics That is spot on. I mistakenly assumed 5 was volts...

[@Thamer03]

What is the name of the program you are using it is really cool

[@FesZElectronics]

Its LTspice - its a free circuit simulator program. I use it in most of my videos.

[@pawank.patidar]

Great sir, please make video fm radio antenna signal amplifier for weak Signals . How to build please guide us.

[@rjameslower]

What if replace RLC oscilador with a xtal ?

[@biswajit681]

Could you make video on 3 phase BLDC motor control methods

[@FesZElectronics]

I may cover this at some point, but it is not currently in plan...

[@ElectronicaJE]

[@visualnetwork3773]

Why did you switch the transistor fron 2222 to 2219 ?

[@FesZElectronics]

It was capable of delivering higher power, so it was also more resistant to misuse.

[@troy6882]

Education and we know aaaaaaaa.😁it's working good timing!... ...that took a lot off direction correction including electron roll on a dead half line??..😳WTH!.🤣.

[@ibrahamdavide4556]

PLEASE MY FRIEND YOUR SPEECH FOR STUDENTS JUST . IF YOU CAN EXPLAIN FOR US . HOW CAN WE MAKE TANK CIRCUIT ? WHICH IS PART FROM YOUR AMPLIFIER CIRCUIT . MY SWEET GREETINGS FOR YOU

[@TWOSU_NEWS]

My brain hurts

[@imadsalem1446]

What is simulator name

[@FesZElectronics]

Its LTspice - this is what I use in all my videos

[@fullwaverecked]

So class C not so good for guitar amp?

[@FesZElectronics]

Most likely not, but you can try it - in the simulator at least; it might create some interesting sound effects. I did a video a long time ago about how audio files can be imported and exported into LTspice. kzbin.info/www/bejne/o5WtnmCKr9d1qaM

[@fullwaverecked]

@@FesZElectronics I'll check it out. BTW, I'm interested in low wattage (2 - 12 watts) guitar amp builds. Thanks for responding and keep up the great work!

[@fullwaverecked]

I don't know why RF is so hard to wrap my poor brain around... 😵‍💫

[@bradleyberthold4606]

I believe in real Class-C amps they just put a very large inductor in the collector, to keep it operating in continuous current mode, and then the output has the LC matching which acts also like a filter to get the required frequency (you put in a PI filter) (see an example at kzbin.info/www/bejne/nJ29m3Wnnsh6iqc&ab_channel=MahendranC). Having the "LC tank" in the collector is too difficult to get a good signal since the load will load down it's Q and then you get discontinuous operation.....all the real schematics I've ever seen for Class C, don't use a LC tank in the collector, they use a large inductor in the collector for continuous current, and then the output network is a matching network connected to a filter which will give you the frequency of interest - the input frequency is what determines the real frequency of operation more than anything. Class C is basically a "DC - DC converter" that doesn't rectify the signal and has a filter at the frequency of interest instead of a super low pass filter.

[@cheifreal]

So a class c is the hit and mis engine of the rf world. Makes since ta me.

[@jimlahey5354]

He hasn't slept in 6 days

[@fullwaverecked]

Large amounts of distortion is a crappy guitarist's dream. Just speaking for myself. 😎