(4) Transistors, Logic gates, EM spectrum, electrochemistry half cells

BJT vs FET transistors. Transistor as electronic switch. Analog switches; switching speeds
Transistor as "back to back diodes",
Braitten, Bardeen and Shockley, Bell Labs, 1949
doping silicon crystal: column 5: phosphorus for n-type, column 3: boron for p-type

BJT thickness 1 micron of base region; emitter more doped than collector;
AZ: electrons moving across E-B junction can diffuse across base to collector and then move up; a few holes go the opposite direction. See energy vs distance curve for another POV.
What happens if base is too thick? recombination...

Wikipedia: To minimize the percentage of carriers that recombine before reaching the collector–base junction, the transistor's base region must be thin enough that carriers can diffuse across it in much less time than the semiconductor's minority carrier lifetime. In particular, the thickness of the base must be much less than the diffusion length of the electrons.
common emitter inverter; Ic/Ib current gain = 100
emitter follower circuit: a GFI solenoid in the follower.

phototransistor and photons releasing electrons in base.
2N4401 and heat sink.

FETs: better saturation voltage, better freq response. High input impedance.

Horowitz and Hill, The Art of Electronics

ref: Digital Design from Zero to One, John Wiley & Sons, 1996.
Logic Noise Margins
for example the TTL (bipolar junction transistor logic family 7400 series)
Vcc the supply voltage is guaranteed between 4.75 and 5.25 v; below 4.75 chips may not work as advertised; above Vcc-max 7.0 volts chips may be permanently damaged.
Logic LO = 0 = FALSE = inactive = open switch is between 0v and 0.8v
Logic HI= 1= TRUE = active = closed switch is above 2.2v up to 5.0v
Region in TTL between 0.8 and 2.2 is "not allowed"
Noise Margin represents the advantage of digital or analog representation; a digital recording can be faithfully reproduced, whereas reproduction of an analog "master tape" will always be degraded...

To change from LO to HI the voltage of the TTL logic gate must pass through the noise margin region--as quickly as possible--nanoseconds. An voltage between 0.8 and 2.2 must be "converted" to 0 or 1, from its metastable region. TTL chip mfgrs make chips that have stable outputs only for logic 0 or logic 1... same for any other chip family...

Base 2 numbers, hexidecimal representation: 0 1 2 3 4 5 6 7 8 9 A B C D E F
in base 2, C = 1 1 0 0
in C++ code for IAR editor hex code is 0xCF = decimal 12*16 + 15 = 207

Combinatorial Logic: logic gates "without memory" circuits without feedback.

7400 series hex inverters: input hysteresis 7414,
open collector output 7406...interface between voltage levels, drive LEDs...

0 0 0    0
0 0 1    0
0 1 0    0
0 1 1    1
1 0 0    0
1 0 1    0
1 1 0    1
1 1 1    0

Realize as "Sum of Products" AND to OR two-level circuit

: logic circuits with memory, with feedback.
Set Reset Latch with output Q
S R   Q
0 0    no change: the memory state! 
0 1    0 (RESET)
1 0    1 (SET Q to logical 1)
1 1    not allowed!

toggle flip flops


states, and Finite state machines.

instructions: source, function, destination.

Coding, functions, interrupts.

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Electromagnetic radiation spectrum:
power lines, radio, microwave/radar, infrared, visible, ultraviolet, x-rays, gamma rays, cosmic rays.

half cells of electrochemistry

Reference for BMEs:
G. Bendek & F. Villars, Physics with Illustrative Examples from Medicine and Biology:
vol 3, Electricity and Magnetism