transistors
I'm pretty new to circuits, and still don't know exactly how transistors work, but when I search up a tutorial for circuits that include Transistors, they all have in the title, "One Transistor This", "One Transistor That".
Is there any specific reasoning behind that?
What is so special about Transistors?
Why not include "2 Capacitors"?
Example, I searched up "One Transistor FM Receiver", I know that's a little cheaty, but WHY do all these video's have it in the titles?
NMOS connected in diode configuration:
simulate this circuit – Schematic created using CircuitLab
Since Gate and Drain are shorted, the following saturation condition always holds:
$$V_{DS}>V_{GS}-V_T$$
This means that once \$V_{DS}>V_T\$ the transistor both begins to conduct and enters saturation.
In saturation (after substitution \$V_{GS}=V_{DS}\$ for diode mode):
$$I_{DS}=\mu C_{ox} \frac{W}{2L} (V_{DS}-V_T)^2$$
The equivalent resistance of this device is:
$$R=\frac {V_{DS}}{I_{DS}}=\frac{2L}{W} \frac{1}{\mu C_{ox}} \frac{V_{DS}}{(V_{DS}-V_T)^2}$$
Now you can see that the equivalent resistance can be controlled by changing the dimensions of the transistor (\$W\$, \$L\$).
However, this resistance is not constant - it depends on the applied bias. This is bad, but it is not that you have too many alternatives in integrated circuits (you can implement precision resisters by various techniques, but they are usually costly).
On the positive side - there are many application which do not require precision in resistances.
Can you implement a big resistor with diode connected transistor? Yes. There are two approaches:
However, "big" resistor in integrated circuit is not the same as big resistor as discrete component - in integrated circuit all resistances are relatively low.
Your question distills to "how should I use transistors?" and the answer fills whole books. Distributors carry tens of thousands of different transistors to meet the needs of designers. As a consequence, I don't believe you can create an infographic that is complete, correct, and useful at the same time.
What I can give you is a set of heuristics:
Choose...
...a BJT when:
you need a current amplifier¹
you have power to burn, so the required base current doesn't bother you
the "bottom leg" of the transistor can get pulled above the "top leg," and you need this path to not conduct when that happens, as it would in a MOSFET due to the body diode
you need to exploit the C-B or E-B diode²
...a JFET when:
you only need small-signal amplification³
the base current of a BJT would be a problem in your application⁴
you need a voltage-controlled resistance
you need higher transconductance or lower flicker noise than you'd get with a MOSFET
you need a small, discrete, low-component-count constant current source
...a MOSFET when:
you need a switch⁵
you need higher input impedance than a BJT, and can't find an IGBT that fits the bill
you can't find a JFET studly enough to control the power your circuit needs⁶
you were looking at JFETs, but then realized you needed enhancement mode operation⁷
you want to exploit the inherent body diode as a feature, rather than consider it a problem to cope with⁸
...an IGBT when:
I've largely ignored transistor combinations above, because once you start combining transistors, the possibilities literally become infinite. Today you have a range from Darlington pairs to billion-transistor ICs, with new circuit arrangements being designed all the time.
There are many, many more types of transistors, but for the most part, you want to figure out all the above before moving on to them. The others are usually derivatives of the above classes, so without the initial grounding, you will have no basis to select one of the exotics. Examples:
Need to exploit the fact that a BJT's base is light-sensitive when not encapsulated? Okay, that's a phototransistor.
Need multiple emitters or collectors on your BJT? Sure, no problem, that’s easy to create in silicon; it’s often useful and therefore often seen at the custom silicon level.
Need a BJT, but a whole lot faster? Okay, we just won't use doped silicon for everything, we'll combine materials into a heterojunction transistor.
Need to pack transistors in even tighter than normal, but running into trouble with the short channel effect? Okay, we'll give you a FinFET.
Need something that works kinda like a diode, and kinda like a BJT? Okay, we'll blur the lines for you and give you a UJT.
Need something like an IGBT but with lower loss and higher current gain? A SiC junction transistor might be what you're looking for.
Footnotes
You can also make voltage amplifiers with bipolars, of course.
Small-signal BJTs make great low-leakage diodes.
JFET-like power devices exist, such as Infineon's CoolSIC, but they're relatively new and exotic, thus expensive.
This is why there are so many JFET-input op-amps.
All the other transistor types can act as a switch, too, but MOSFETs excel at this.
A power MOSFET isn't quite the same thing as a power JFET,³ and it isn't the only alternative, but it is often the simplest, cheapest alternative.
JFETs are inherently depletion-mode devices, only.
One my answers here at EE.SE shows such a circuit.
Best Answer
Once upon a time, transistors were likely to be the most expensive part in a simple amplifier or oscillator design. Even today, a discrete transistor is likely to be 2 to 10 times as expensive as a discrete resistor or capacitor.
So a "one transistor" circuit was roughly half as expensive to build as a "two transistor" circuit. And cost was an important reason to prefer circuits with fewer transistors.