#1705

Рет қаралды 8,905

IMSAI Guy

7 ай бұрын

Episode 1705
use your NPN backwards!
PIN Diode Switching: • #934 PIN Diode Switching
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Пікірлер: 57

@absurdengineering 7 ай бұрын

Common base configuration works great for digital level shifting. Put the base at Vthreshold+/-0.6V, drive input into the emitter. Then the output is a unipolar current sink that’s active on one side of the threshold voltage. A complementary common base pair can be then followed by current amplifiers that swing the output up and down. Those amps can be clamped to prevent saturation to keep them fast. It’s just one of the many ways of doing it for sure though.

@manitoba-op4jx 7 ай бұрын

what an excellent idea. communicated well, too. i'm going to use this in my 8086 projects!

@ke9tv 7 ай бұрын

The low input impedance is nasty, but so is the temperature dependence of r_e. So the gain is not stable with temperature ad needs to be controlled with feedback somewhere. (In a cascode, the feedback is degenerative.) You should definitely cover cascodes. Cascodes are definitely a Swiss Army Knife transistor circuit. They're essential for high voltage . You use a series of common-base amplifiers at successively higher base voltages to get around limitations of Vce and Vcb. They stabilize current mirrors, because they remove the Early effect by holding the collector voltage of the output transistor constant. They're essential to high-frequency operation, by being Miller killers. If you look at the internals of an OTA like the CA3080 or the LM13700, you'll see veritable towers of cascodes. Both collectors and emitters are supplied by Wilson mirrors (cascodes!) and the differential amp is a cluster of six transistors (a matched pair of Darlingtons driving common-base amps). All to keep the current gains stable and predictable. Cascodes are all--around "make BJT's behave" circuits. And they're the principal use of common-base amps. Back in the day, a 'cascode' was a specialized vacuum tube (@glasslinger might explain it as a 'GlassFET'!) that usually had five grids: control, screen, a grounded grid, a second screen and a suppressor. The effect was the same - the second grid-screen pair was a "grounded-grid amplifier" which is about the same thing as a common-gate amplifier on an FET. You'd usually find them packaged along with a triode, because the other application of the pentagrid was as a mixer, and it was convenient to have the local oscillator in the same device. The other place that common-base circuits used to appear was in receiver input circuits, where the low input impedance was easier to match to the receiving antenna. (It's a lot easier to match 50 ohms to 26 ohms than to infinity!) But now most preamps use FET's instead, in an entirely different configuration. Up in the microwave region, the commonest input circuit uses a dual-gate MOSFET, which is essentially an FET cascode in a single transistor.

@IMSAIGuy 7 ай бұрын

yes, I should do a cascode. I did one: kzbin.info/www/bejne/d4G4maBoqdh2n6csi=SdkCeh4Mkm8rLsHR and covered one in microphone preamps: kzbin.info/www/bejne/qHuaeHRtp6apY7Msi=PXb1YRXd1-4t33Ly

@IMSAIGuy 7 ай бұрын

Even at HF you see a lot of dual gate FETs on the input preamp connected to the antenna, designed in ham radios. usually the thing you have to replace when too much static electricity zaps the front end.

@stamasd8500 7 ай бұрын

@@IMSAIGuy haha yeah I remember hunting 40673s to build better input stages for my ham rig back in the day

@IMSAIGuy 7 ай бұрын

I've seen dual gate mosfet preamp with the two gates tied together. makes no sense to me

@stamasd8500 7 ай бұрын

@@IMSAIGuy gets a little more gain per stage, at the price of negating the benefit of the cascode configuration. I never used them that way.

@fredflintstone8048 7 ай бұрын

I've always struggled fully understanding common base transistor amplifier circuits. Common emitter, common collector, no problem. Thanks for explaining the circuit in a way that's helpful to me.

@eevibessite 7 ай бұрын

kzbin.info/www/bejne/gqPElZV-ibGJhrs

@Soundfactory24 7 ай бұрын

Such common base circuits are often found in old RF circuits (70s), mostly with germanium transistors. The transit frequency could therefore be used effectively.

@dhpbear2 7 ай бұрын

I 'm surprised the transistor's small-signal gain (hFE) doesn't affect the overall gain. Now that I see, in this configuration, that the input current *EQUALS* the output current!

@IMSAIGuy 7 ай бұрын

yes, very different from the typical transistor stuff.

@PapasDino 7 ай бұрын

I like your "wiggle" description so much I use it teaching classes now and how I think about stuff at the workbench as well. TNX! 73 - Dino KLØS

@rfburns5601 7 ай бұрын

My trade school memories: Common collector - unity voltage gain - has current gain Common emitter - more voltage gain than current gain Common base - more current gain than voltage gain?? But hey, I'm getting old. I do remember common base is like grounded grid - low input impedance and self neutralizing. That's why these are almost always seen in vhf fm receivers as an rf amp. Low input impedance - ideal for antenna coupling, self neutralizing - less likely to oscillate and reduces local oscillator coupling to antenna. I remember as a student getting hung on identifying CC,CE, or CB amps is that the common element is at SIGNAL ground, not necessarily bias voltage ground. For example common collector amps, the collector is at signal ground through the power supply.

@IMSAIGuy 7 ай бұрын

common base has unity current gain www.electronics-tutorials.ws/amplifier/common-base-amplifier.html

@stamasd8500 7 ай бұрын

@@IMSAIGuy actually the current gain is a little sub-unity; the output (collector) current will be the input (emitter) current minus the base current.

@IMSAIGuy 7 ай бұрын

beta/(beta+1)

@bayareapianist 7 ай бұрын

I remembered reading this in an old book. When HF transistors were expensive and germanium Tr's were slow, CB circuits were mostly used at the RF side since CB has a lowest capacitance to ground. It was before JFET time and pocket radios had to use germanium Tr's due to their lower voltage drop.

@stamasd8500 7 ай бұрын

@@bayareapianist even early Si transistors were used mostly in common base configurations in RF - no Miller effect means they could be used at reasonable frequencies. But the low input impedance means they had to be used with tuned circuits on the input (and output) so they were narrowband. I remember using BF173s that way. Wideband RF amplifiers had to wait until better transistors came along.

@deepblueskyshine 7 ай бұрын

Back in the days this was a very common first stage RF amplifier.

@eevibessite 7 ай бұрын

kzbin.info/www/bejne/gqPElZV-ibGJhrs

@christopherventer6391 3 ай бұрын

A version of this configuration is used in Spectrasonics microphone preamps and was used in their consoles back in the 60s. The reason why is the guy who designed them worked on missile guidance systems so he was drawing on his knowledge of high frequency amplifiers. As a result, they are really good at handling transients, actually. This was the type of console they had at the record plant and was used on some of the later Jimi Hendrix recordings as well as John Lennon records. Nowadays they make them in 500 series modules and they sound awesome.

@tlmoller 4 ай бұрын

This is very common with an emitter follower before and after. Give very low distortion and good high frequency response.

@richiet7933 5 ай бұрын

The Bob Ross of electronics :)

@allanpatterson7653 5 ай бұрын

Used in the CRT color gun for RGB to drive cathodes with video beam.

@CarlosChavez-gs1ld 7 ай бұрын

THAT is a calculator.✅ I owned an HP-41CX for many years. Those buttons NEVER fail! 😍 I have built and worked on a number of amplifiers in my life, and I MAY have studied the common base amplifier back in the day, but I don't remember it at at this point. When I saw the circuit, I was sure you had smoked something interesting- until you explained it- well done. The reason it was so hard for me to "get" this circuit, is because I always think of the input to any amplifier being the BASE of a transistor. You could title this video "Using a transistor emitter as the input to an amplifier". YES- the input and output impedances are not ideal, but the circuit is an interesting one anyway. That Rigol scope looks half was decent.

@IMSAIGuy 7 ай бұрын

Rigol: kzbin.info/www/bejne/m5LSeYyNjrGFjJIsi=KoQ7Ub13rt-fCOH-

@massriver 7 ай бұрын

Input signal high. Gain is going from double to half over input.

@robinbrowne5419 7 ай бұрын

When I first saw the thumbnail I thought What kind of weird wizardry is that. But now it makes sense so thanks for the fun and informative video 👍⛄

@fer_fdi 7 ай бұрын

Nice!

@JonDeth 3 ай бұрын

I'm assuming you're using the conventional current path standard intentionally. I'll never be a fan of it lol. It's useful in analyzing existing circuit architecture in some cases, but when learning fundamental topology and the quantum mechanics of devices, I have always favored the electron path standard. It makes unique designs from the ground up much easier to understand and produce in my experience.

@sneakerNetTeckie6630 4 ай бұрын

What do you by wiggles? Other than that great video.

@KeritechElectronics 7 ай бұрын

Don't turn it around or the electrons will fall out! :D

@haraldlonn898 7 ай бұрын

How is the clipping when you over power the transistor. Thinking of distortion like when you use tubes or bulbs? Great info. Thanks

@eevibessite 7 ай бұрын

kzbin.info/www/bejne/gqPElZV-ibGJhrs

@SeanPorio 5 ай бұрын

I’ve seen this used in a microphone preamp in a really old mixer… unbalanced ofc 😵‍💫

@rdormer 7 ай бұрын

Student here. I tried to build this but it's really confusing how - where does the input go? Where do I attach the scope probes? I built it as I understand the schematic but I'm getting nothing out of it, just a flat line. And what's an mf? Is that a microfarad?

@IMSAIGuy 7 ай бұрын

input on left, output on right, uf is microfarad. did you use both +V and -V it needs the negative voltage

@rdormer 7 ай бұрын

@@IMSAIGuy Thank you!