Transistors 101

In my last issue on binary format, I mentioned that transistors are the building blocks of modern computers. That's a specific purpose, though. In a broader sense, transistors are the fundamental building blocks of modern electronics, enabling a wide range of devices, from computers and smartphones to medical devices and automobiles. Transistors are like the LEGO bricks of modern electronics—small, simple pieces that build up to incredible things. The latest smartphones have billions of these incredibly tiny components.

They are tiny electronic switches that make digital logic and processing possible by controlling an electrical signal representing the two states—on and off. These two states naturally map to the binary values 1 and 0, respectively.

Modern transistors in digital electronics mainly consist of three parts: gate, source, and drain. When voltage is applied to the gate, it creates an electric field, opening a path between the source and the drain.

What exactly do they do?

Although transistors are versatile devices with various applications, they fundamentally act as either high-speed switches, the heart of digital devices, or signal boosters, amplifying sounds and radio waves in everyday electronics. However, the two primary uses for transistors are switching and amplification.

Switching, in general, refers to turning signals on and off extremely quickly. A simple example you see every day is when the screen turns on instantly when you press the power button on your smartphone – that's transistors switching on the display. This is a primary function in all digital circuits, like CPUs, GPUs, RAM, memory etc.

Amplification, on the other hand, is the process of making a weak signal stronger. For example, speaking into the microphone on your phone creates a tiny electrical signal. Transistors in the microphone circuitry amplify this weak signal so that it can be clearly understood by the person on the other end of the call or recorded correctly. This use case is prevalent in camera sensors, microphones, radios, etc.

Beyond switching and amplification, transistors are also used for signal modulation (4G/5G/Wi-Fi), voltage regulation (battery management), clock generation, signal conversion (ADC/DAC), light sensing (ambient light detection), filtering, and motor control (haptics)—all essential in smartphones.

Why are transistors important?

Think about the device you're using to read this right now. Its power, its portability, its very existence? You can thank the humble transistor. These tiny components have become the foundation of the digital revolution. Their importance boils down to their incredible size, astonishing speed, minimal power consumption, and remarkable reliability.

Before transistors, bulky machines like vacuum tubes – think of a light bulb – powered electronics. Transistors made it possible to shrink computers the size of rooms into something that fits your pocket: your phone. They can operate on incredibly low power, making the devices truly portable—you need not always be tethered to a power source, after all. The lightning speed with which they switch electrical signals makes them excel at complex processing and communication. Plus, they work with the reliability of clockwork -- your laptop or phone might crash occasionally, but it’s rarely because a transistor failed. It’s usually software or a temporary glitch. The transistors themselves keep going.

Add their low cost of mass production, and you have the pulse of the modern digital civilisation.