EE 2115-01 - Lec 11 - 2026_09_18

Overview

Hiren Trada explains comparator operation through the rule that the output switches to the positive rail when V+ exceeds V− and to the negative rail when V− exceeds V+. He compares resistor pull-ups with complementary transistor switching, introduces CMOS inverter operation, and analyzes an LTspice comparator with ±5 V rails and a 100 mV, 1 kHz sine-wave input; the class concludes with semiconductor manufacturing career paths at companies including TSMC, Intel, Samsung, and Micron.

Key takeaways

A comparator's output is determined by input ordering: V+ greater than V− selects the positive rail, and V− greater than V+ selects the negative rail.
Comparator inputs control the output decision, but the output's energy comes from the external power supply, not from the input signal.
A continuously conducting pull-up resistor wastes steady-state power; complementary push-pull switches reduce that loss by keeping one switch off while the other is on.
A CMOS inverter pairs P-channel and N-channel MOSFETs so a low input produces a high output and a high input produces a low output.
With ±5 V supplies, VIN+ grounded, and a 100 mV, 1 kHz sine wave on VIN−, the comparator produces a rail-to-rail square wave, positive during negative input half-cycles and negative during positive half-cycles.
Semiconductor fabrication offers cross-disciplinary career opportunities, but facilities require major capital investment, with ASML EUV lithography machines costing approximately $180 million to $300 million.

Chapters

0:00 Quiz Timing and the Importance of Dual Power Supplies

Hiren Trada says quizzes will likely occur weekly on Wednesdays, with confirmation about the first quiz to come by announcement.
The class reviews dual power supplies, a foundation for understanding comparators and op amps.

1:19 Comparator Inputs Select Between Positive and Negative Rails

When V+ exceeds V−, the comparator output switches to the positive supply rail; when V− exceeds V+, it switches to the negative rail.
Comparator input terminals make the decision, while separate power-supply terminals provide the energy and voltage levels available at the output.
The input difference can be very small, such as 1 mV versus 2 mV, while the output switches to system-level supply voltages.

4:47 How an Internal Switch Produces Comparator Output

A decision-making circuit controls a semiconductor switch according to the relative input voltages.
In the illustrated pull-up arrangement, the output connects to VCC through a resistor when the lower switch is off.
When V− exceeds V+, the switch turns on and connects the output to the negative rail, VE.

8:36 Complementary Switches Replace the Pull-Up Resistor

A pull-up resistor continuously dissipates power in the described circuit because current flows through it at steady state.
Replacing the resistor with a complementary transistor switch reduces steady-state power loss: one switch is on while the other is off.
The paired switches form a push-pull output stage that selects between supply rails.

12:30 BJT, MOSFET, and CMOS Inverter Basics

Bipolar junction transistors use PNP or NPN semiconductor structures and conduct through both positive and negative charge carriers.
MOSFETs are available as N-channel and P-channel devices; pairing complementary N-channel and P-channel transistors forms CMOS.
A CMOS inverter applies the same input to both transistor gates: low input turns on the P-channel device and pulls the output high, while high input turns on the N-channel device and pulls it low.

19:00 LTspice Comparator Simulation with a Sine-Wave Input

The simulation uses a dual supply with a grounded midpoint, setting VCC to +5 V and VE to −5 V.
VIN+ is held at 0 V while VIN− receives a 100 mV sine wave at 1 kHz, so it alternates above and below the reference.
A sine wave repeats 1,000 times per second in this example and has peaks of +100 mV and −100 mV.

25:00 Predicting the ±5 V Comparator Square-Wave Output

The comparator output is a two-level waveform, switching between +5 V and −5 V rather than following the sine-wave shape.
With VIN+ at 0 V, a positive VIN− makes V− greater and drives the output to −5 V; a negative VIN− drives the output to +5 V.
Because the input sine wave spends equal time above and below zero, the output is a square wave with equal high and low durations.
LTspice plots the input and output over a 3 ms interval, and students are expected to run the simulations themselves.

35:20 Semiconductor Manufacturing Careers and Campus Cleanroom

Trada describes Cal Poly's cleanroom as a semiconductor fabrication facility and notes that related interdisciplinary classes have limited seats and are typically offered once a year.
He points to hiring and manufacturing activity at TSMC in Arizona, Intel in Arizona and Ohio, Samsung in Texas, and Micron in Idaho.
Semiconductor manufacturing employs engineers, technicians, and supply-chain workers across engineering and scientific fields.
Extreme ultraviolet lithography machines made by Dutch company ASML cost roughly $180 million to $300 million each, illustrating the scale of investment in fabrication facilities.

Summary, takeaways, and chapters were generated by AI from the video's transcript and may contain errors. The video belongs to its creator, Hiren Trada.