Really well explained. I do find jfets quite tricky to get my head around and I'm using this video as a supplementary aid to my textbook coverage of this section. I don't know why this video appears 7th on the list when I enter 'jfet biasing' in my UA-cam search. It should appear at number 1. Nice video. I look forward to watching your other videos.
You are certainly not the first person to comment on the fact that many of my videos are buried in the recommendations. I guess "the algorithm" doesn't like the fact that I haven't monetized my channel, don't have sensationalist titles, and there are no mentions of celebrities! Who knows... Anyway, glad you liked it, and in case you are not aware of them, be sure to download my free textbooks on the subject (links in video description).
Pretty much, assuming it's using self bias and the manufacturer didn't optimize the device for something other than a small signal amplifier. It will also work for P channel and DE-MOSFETs.
Thank you. I have questions but probably worth waiting for the amplifier sections. The text is excellent, by the way. The question that keeps getting in the way of me listening to you is about the size of the Gate resistor and noise in an audio signal path. Would we use Fets in Audio HiFi, Are there pros and cons on noise?
Replay starting at 16:00. What I drew is a quick sketch of the self bias curve which can be found in my Semiconductor Devices text (a free Open Educational Resource, see download links in the video description above). You would simply read the value of 0.38 off of the vertical axis, and then multiply that by Idss to find Id. The graph is, in fact, the curve of an equation that is derived in the text. If you wanted to, you could plug all of the values into the equation, but the graph version is a bit quicker.
Good afternoon! This is a best material about JFET, that i found in Internet. But maybe I’m wrong, and it seems to me that the x-axis should be not value (Gm0)*Rs, but value (Gm*Rs). Is the Gm0 constanse for this transistor? I should not understand last graph.
gm0 is a constant. It's the value of gm at Vgs = 0V. gm0 helps define the steepness of the curve. The x-axis is indeed gm0 * Rs. This curve is derived in chapter 10 of my free Semiconductor Devices text (see download link in video description).
Good question. Stability for JFETs is a little more complicated than it is for BJTs. In a BJT, gain is dependent on r'e, which in turn is dependent on Ic. Thus, if you have high Ic stability, then you also have high gain stability (which is the target). For JFETs, gm is analogous to r'e, but it does not have the same sort of relation with Id. Therefore, high stability for Id does not necessarily mean high stability for gain. Thus, we have to be careful what we're asking about here. It turns out that self bias is a special case of what I call combination bias in the Semiconductor Devices text (and which voltage divider bias is a single supply variation of). In general, combination bias achieves a more stable Id than self bias, and using a proper design, can achieve higher gain stability. Unfortunately, one of the downfalls of the voltage divider configuration is that the divider resistors produce a decreased input impedance. In actual practice, a self bias circuit may have all the stability that is needed, and uses a minimal configuration.
@@ElectronicswithProfessorFiore Hi, Thanks for answering this complicated task. Yes input voltage bias network decreases the input impedance. In my mind i was thinking about the old 600 Ohm audio transmission standard. A input biasnetwork with maybe a 1M and 200K voltage divider is negligible when the signalsource is 600 Ohm. But of course with a selfbias setup you dont have to worry so much about the impedance of the signalsource, unless the signal comes from a function generator with 50 Ohm output impedance 😉
Really well explained. I do find jfets quite tricky to get my head around and I'm using this video as a supplementary aid to my textbook coverage of this section. I don't know why this video appears 7th on the list when I enter 'jfet biasing' in my UA-cam search. It should appear at number 1. Nice video. I look forward to watching your other videos.
You are certainly not the first person to comment on the fact that many of my videos are buried in the recommendations. I guess "the algorithm" doesn't like the fact that I haven't monetized my channel, don't have sensationalist titles, and there are no mentions of celebrities! Who knows...
Anyway, glad you liked it, and in case you are not aware of them, be sure to download my free textbooks on the subject (links in video description).
Can the self biasing graph on page 280 of the text be used for biasing any n-channel JFET on the market, regardless of datasheet specs?
Pretty much, assuming it's using self bias and the manufacturer didn't optimize the device for something other than a small signal amplifier. It will also work for P channel and DE-MOSFETs.
Thank you. I have questions but probably worth waiting for the amplifier sections. The text is excellent, by the way. The question that keeps getting in the way of me listening to you is about the size of the Gate resistor and noise in an audio signal path. Would we use Fets in Audio HiFi, Are there pros and cons on noise?
Yes, we use FETs in audio circuits. The gate resistor can be large, but it's not in-line with the signal, it's in parallel.
@@ElectronicswithProfessorFiore Ugh! Of course it is. Thank you.
Still confused as to how you know Id = .38. What equation was used to find this value?
Replay starting at 16:00. What I drew is a quick sketch of the self bias curve which can be found in my Semiconductor Devices text (a free Open Educational Resource, see download links in the video description above). You would simply read the value of 0.38 off of the vertical axis, and then multiply that by Idss to find Id. The graph is, in fact, the curve of an equation that is derived in the text. If you wanted to, you could plug all of the values into the equation, but the graph version is a bit quicker.
Good afternoon! This is a best material about JFET, that i found in Internet. But maybe I’m wrong, and it seems to me that the x-axis should be not value (Gm0)*Rs, but value (Gm*Rs). Is the Gm0 constanse for this transistor? I should not understand last graph.
gm0 is a constant. It's the value of gm at Vgs = 0V. gm0 helps define the steepness of the curve. The x-axis is indeed gm0 * Rs. This curve is derived in chapter 10 of my free Semiconductor Devices text (see download link in video description).
how did you get 3.8
See my reply to Sachems64, below.
Is a voltage divider bias setup more stable than a self bias setup?
Good question. Stability for JFETs is a little more complicated than it is for BJTs. In a BJT, gain is dependent on r'e, which in turn is dependent on Ic. Thus, if you have high Ic stability, then you also have high gain stability (which is the target). For JFETs, gm is analogous to r'e, but it does not have the same sort of relation with Id. Therefore, high stability for Id does not necessarily mean high stability for gain. Thus, we have to be careful what we're asking about here. It turns out that self bias is a special case of what I call combination bias in the Semiconductor Devices text (and which voltage divider bias is a single supply variation of). In general, combination bias achieves a more stable Id than self bias, and using a proper design, can achieve higher gain stability. Unfortunately, one of the downfalls of the voltage divider configuration is that the divider resistors produce a decreased input impedance. In actual practice, a self bias circuit may have all the stability that is needed, and uses a minimal configuration.
@@ElectronicswithProfessorFiore Hi, Thanks for answering this complicated task. Yes input voltage bias network decreases the input impedance. In my mind i was thinking about the old 600 Ohm audio transmission standard. A input biasnetwork with maybe a 1M and 200K voltage divider is negligible when the signalsource is 600 Ohm. But of course with a selfbias setup you dont have to worry so much about the impedance of the signalsource, unless the signal comes from a function generator with 50 Ohm output impedance 😉
@@royrogers7644 600 ohm audio... Now you're taking me back to the old days. Kind of glad that we moved past that!