Its really great that you're explaining transistor biasing and why it has to be the way it is for [amplifiers]. I am deep into building my first superhet receiver and I would like to know how a bipolar transistor is supposed to be biased to make an amplifier stage into an RF mixer. I know RF mixing ("multiplying") happens when a device is non-linear. But what I would like to know is where is the "happy place" for an RF mixer. Maybe a mini series on bipolar transistors used to heterodyne?
@IMSAIGuy3 жыл бұрын
I haven't looked at it but try this: www.nxp.com/docs/en/application-note/AN238.pdf
@markjacobsen3023 жыл бұрын
@@IMSAIGuy Thats pretty cool and I think it will be useful. But I still would like to see how you explain it in a video. If you don't want to that's ok. I understand. But I do enjoy watching your vids and I really get a lot from the way you explain things because of your teaching method. I don't know - but I hope you decide to make one about this.
@absurdengineering Жыл бұрын
Transistors are non-linear enough that they will heterodyne whether you want them or not without taking special precautions. Various biasing schemes then control how much signal you get out, and that’s the big deal. If you feed any two frequencies to any common single-transistor amplifier, you get their modulation products in the output. It takes some work for transistors not to do that :)
@PapasDino3 жыл бұрын
I find the easy way to keep the amplifier types straight is to look for the common AC signal ground which then gives you the "common" type. Nice explanations!
@RicardoPenders3 жыл бұрын
Thank you for explaining what common emitter means, I knew what it was and what it did but I didn't get the common thing, English isn't my first language but now I understand what it exactly means, I very much appreciate that.
@joedambrosia6896 Жыл бұрын
Incredible! Thank you!
@rmwagar818 Жыл бұрын
I am a 75 year old hobbyist and I learn much from your videos on every subject and I practice with your circuits, I would like to know what Input capacitor you use on the input in the circuit, is it one of your favorite .01 thank you
@IMSAIGuy Жыл бұрын
depends on the frequency. for high frequency 0.01 or 0.1 is fine. for audio circuits you might need 10uf
@RexxSchneider2 жыл бұрын
Transistors don't have a "linear region". The base-emitter voltage vs collector current transfer characteristic is always exponential so you're wasting your time trying to find a linear portion. You might as well bias the collector so that you can have a symmetric swing both positive and negative before clipping occurs. Without any feedback, you'll always have harmonic distortion from this biasing arrangement.
@SheikhN-bible-syndrome Жыл бұрын
So then what has to be added and where?
@RexxSchneider Жыл бұрын
@@SheikhN-bible-syndrome You need some form of negative feedback to reduce the inherent distortion. That could take the form of an emitter resistor (between the emitter and ground). A value for that resistor such that about 250mV is dropped across it will reduce the distortion (and gain) by a factor of about 10. Either instead of an emitter resistor or in addition to it, you can replace the biasing resistor from supply to base with a feedback resistor from the collector to base. Using a resistor about half the value of the one replaced will retain the biasing approximately, but will reduce gain and distortion appreciably.
@AdrianBoyko3 жыл бұрын
Very helpful!
@lucaacciarri84885 ай бұрын
is there an AC input signal on the left side of the capacitor? thanks for these great videos
@IMSAIGuy5 ай бұрын
yes, it is an AC amplifier
@stevehunt21252 жыл бұрын
I’m a bit confused. In your first video you showed it saturating with a base voltage of about 0.9V but you’re biasing it at 4V. Huh?
@davidh1187 Жыл бұрын
The 4v "Happy Place" was on the output not the input so he adjusted the voltage at the base to achieve a 4v output. What was not explained was that the active Vb zone (from approx 560mV to 890mV), limits the amplitude of the input AC signal before distortion occurs. In video 1 he used 1v amplitude (so we could see the start and end points) but since the active range is about 330mV (890-560), the amplitude of the input signal has to drop to less than 330mV or the output will be clipped. Setting the bias point to produce a 4v output was simply to put Vb in the center of the 'Active' zone. Note I have edited this a few times as I am still learning and then observing what actually happens through experiment :)