The 741 op amp is one of the most famous and popular ICs with hundreds of millions sold since its invention in 1968 by famous IC designer Dave Fullagar. In this article, I look at the silicon die for the 741, discuss how it works, and explain how circuits are built from silicon. I started with a 741 op amp that was packaged in a metal can (above). Cutting the top off with a hacksaw reveals the tiny silicon die (below), connected to the pins by fine wires.
Why op amps are important
Op amps are a key component in analog circuits. An op amp takes two input voltages, subtracts them, multiplies the difference by a huge value (100,000 or more), and outputs the result as a voltage. If you’ve studied analog circuits, op amps will be familiar to you, but otherwise this may seem like a bizarre and pointless device. How often do you need to subtract two voltages? And why amplify by such a huge factor: will a 1 volt input result in lightning shooting from the op amp? The answer is feedback: by using a feedback signal, the output becomes a sensible value and the high amplification makes the circuit performance stable.
Op amps are used as amplifiers, filters, integrators, differentiators, and many other circuits. Op amps are all around you: your computer’s power supply uses op amps for regulation. Your cell phone uses op amps for filtering and amplifying audio signals, camera signals, and the broadcast cell signal.
The structure of the integrated circuit
NPN transistors inside the IC
Transistors are the key components in a chip. If you’ve studied electronics, you’ve probably seen a diagram of a NPN transistor like the one below, showing the collector (C), base (B), and emitter (E) of the transistor, The transistor is illustrated as a sandwich of P silicon in between two symmetric layers of N silicon; the N-P-N layers make a NPN transistor. It turns out that transistors on a chip look nothing like this, and the base often isn’t even in the middle!
For more detail: Understanding silicon circuits: inside the ubiquitous 741 op amp