1. Magic smoke is real and you need to embrace it.
Every integrated circuit or electronic component operates using a little-known mystical wonder. We call it the “magic smoke.” This smoke is ethereal, sublime and not completely understood by the scientific method.
Practically, however, it is a distinct and critical part of the component. There is no class that you can take and no book that you can read about magic smoke, but its effects are well-known in the industry.
Magic smoke works like this:
- It is sealed into the component at manufacture.
- The component operates as long as the magic smoke is contained inside of the component.
- If the magic smoke is ever allowed out of the component, the component will no longer function (Figure 1).
- Much like a can of worms, you can’t put magic smoke back into the component.
Therefore, by the observed effects of magic smoke, you can conclude that it is essential to component operation. Common causes of magic smoke release include (but are not limited to) overvoltage stressing, overcurrent stressing, reversed
supply, overheating or incorrect wiring.
2. You’ll never be alone when you work in isolation.
Many electronic systems have multiple different supply “zones.” For example, in a compressor circuit, there will be a high-voltage zone that is several hundred volts to supply power to the motor and a low-voltage
zone where the control circuits live and work. To improve the reliability of these systems, designers use a concept called isolation.
Isolation is a way to transport data and power between high- and low-voltage circuits while preventing hazardous or uncontrolled transient current from flowing in between the two. Isolation protects circuits and
helps them withstand high-voltage surges that would damage equipment or harm humans – even smart humans like analog engineers. Most sane lab practices require that you not be alone in the lab when working on systems that operate at
potentially dangerous high voltages. So if you are working in isolation, grab a buddy and stay safe!
3. Pease Isn’t a Typo.
One of the
greatest legends of analog design was the late Bob Pease. He’s credited with
developing more than 20 integrated circuits, many of them used for decades in the
industry. Bob chronicled his design experiences in a column called “Pease Porridge,”
which ran monthly in Electronic Design magazine (Figure 2 shows one of Bob’s quips, signed with his initials, RAP). He
also hosted the semiconductor industry’s first online webcast, tailored specifically
for analog design engineers.
4. Clocks Are No Good at Telling Time.
Clocks are possibly the most ironically named analog components because a clock won’t give you the time of day. A “clock” is in reality an oscillator typically used to generate a consistent, stable frequency. Clocks
can be a key element of analog design because of interference to and from the clock signal. A clock signal propagating across a board adds noise and accumulates delay. Meanwhile, the clock signal induces noise onto other nets on the board.
Clocks can be messy if not done properly, so it is critical that you understand the purpose of oscillators, generators, buffers and jitter
cleaners in order to optimize your system.
5. There Is a Lot of Drawing Involved for a Field This Technical.
Analog design engineers love to draw. We love to pick up dry erase markers and draw squiggly lines all over a white board. We draw in a language unique to us and undecipherable to the uninitiated (Figure 3). Every major component in a system has its own special symbol, ranging from simple resistors
and capacitors up to complicated blocks like analog-to-digital converters (ADCs) and digital-to-analog converters (DACs). These symbols bring meaning and functionality to a circuit long before anything physical is actually made and provide
a platform for discussion, starting with the phrase “And this is how it works …”
6. V = IR Is Always the Answer.
It is humorous how useful simple concepts can be. Analog design is home to some very complicated integrated circuits: sigma-delta ADCs, RF amplifiers, digital isolators, etc. Yet the most common design equation is
Ohm’s law, a relationship that most people learn in high school or even earlier.
Ohm’s law states that V = IR, or that voltage is equal to current times resistance. Undoubtedly, most of you are rolling your eyes at the fact that I just wasted a whole sentence to describe Ohm’s law, which
everyone already knows.
Let’s take a look at some examples of analog design that don’t require a doctorate in mathematics to solve:
- Current shunt amplifier: A 10mΩ resistor (R) is placed in line with a current up to 10A (I), and the 0-0.1V (V) is
amplified and measured.
- In a precision DAC, at a 5mA (I) load the output drops by 120mV (V), meaning that the output impedance (resistance) is about
24Ω (R).
- In a motor gate driver, a MOSFET overcurrent monitor trips at 0.5V (V), meaning that a MOSFET with an on-resistance of 20mΩ (R) has an
overcurrent threshold of 25 A (I).