Week 2 – Analog Basics¶
This week was an introduction to how analog electronics actually works at a physical level, and how that connects to digital logic.
We started with the water analogy for electricity. Voltage is like water pressure, current is like the flow rate, and resistance is like a narrow section of pipe. Ground is where everything returns. This made it easier to think about circuits as something physical instead of abstract math.
Water Analogy¶
The main takeaway is that higher voltage means more “push,” and resistance limits how much current can flow. Ohm’s Law connects all three, even though we did not go deep into heavy math. Seeing the water analogy applied to transistors was quite helpful.
Passive components¶
After that, we looked at passive components.
Resistors simply reduce current. Capacitors store charge and respond differently depending on how fast a signal changes. Inductors resist changes in current and behave differently at different frequencies. They help smooth out power fluctuations.
The important idea was that capacitors prefer fast-changing signals and inductors prefer slow-changing ones. This will be important to remember when we deal with filtering and signal shaping.
Then we moved into transistors. We talked about NMOS and PMOS and how they act like controllable switches. The water analogy helped again here: a transistor is like a valve that opens or closes depending on a control signal. This is the bridge between analog behavior and digital logic. These images show how
CMOS and Logic¶
We reviewed binary logic and truth tables. A high voltage represents 1 and a low voltage represents 0. From there we looked at AND, OR, and NOT gates. What was useful was seeing how those gates are actually built from NMOS and PMOS transistors.
AND must be all on, OR at least one on, and NOT is opposite.
Instead of thinking of logic as abstract symbols, we traced how the transistors physically connect to either VDD or ground depending on the input combination.
After that, we were introduced to SPICE simulation. SPICE lets us define components in a text-based netlist and simulate how the circuit behaves before physically building it. This is important because it prevents mistakes and helps visualize how signals change over time.
We also briefly discussed clock distribution and why timing matters in digital systems, and we ended with Schmitt triggers. A Schmitt trigger adds hysteresis so noisy signals do not rapidly flip between 0 and 1 near the threshold. That was a good reminder that real-world signals are messy.
Homework Documentation¶
I recreated the AND transistor circuit in tinkercad: https://www.tinkercad.com/things/jEwkAW2N5mF-initial-and-gate-working?sharecode=Vz_vHeraA1JmpQHJuZ1WRbpvBTL80jUjtiYLZPOCcRk
Which I derived from the example circuit:
I ran the transistor AND gate circuit with tinkercad simulation and confirmed that the circuit only goes high when A&B are high.
I then added an inverter to reverse the logic, so that it only goes low when the inputs are both high.
https://www.tinkercad.com/things/acPrx2Yq05V-and-gate-with-inverter?sharecode=5hB4TD1tf38xydDiYf61zBRZ2aQfQ26FtDmnH9F2Dzg
MODIFY NETLIST: I’m not ready to modify the gate netlist. I don’t fully understand how the parts are assigned and don’t know how to run the spice simulation yet. I’m hoping after the next class it’ll click more and I can do this. I can see what a transistor model is written as:
I can see what basic components are written as:
Final Reflection
The most useful part for me was seeing how logic gates are actually constructed from transistors and then verifying that behavior in simulation, and I hope to get more into this so the “logic” sinks in!