Glossary

51 terms that recur across the curriculum. Skim before starting; refer back as needed.

ACK

An acknowledge bit (SDA LOW on the 9th clock)

In I²C, the receiver pulls SDA LOW after a byte to acknowledge it was received.

attenuation

ADC setting that changes the measurable voltage range

Higher attenuation allows measuring higher voltages but may reduce linearity/accuracy.

back-EMF

Voltage a coil generates that opposes the change in its current

By Faraday's law, a changing current in an inductor or motor winding induces a voltage that fights the change. In motors it rises with speed and is used to sense rotor position in sensorless drives.

bathtub curve

Failure rate over a product's life: high, flat, then high again

It combines a falling infant-mortality region, a long flat region of random failures, and a rising wear-out region, tracing a bathtub shape. Burn-in screens out the early-failure population before shipping.

boundary scan

Testing board interconnects by shifting bits through chip pins

Cells around each I/O pin form a shift register accessed over JTAG, letting you drive and read pin states to find opens and shorts between chips without physical probes. Standardized as IEEE 1149.1.

buck converter

A switching regulator that steps voltage down efficiently

It rapidly switches an inductor to step the input voltage down while stepping current up, wasting little power as heat. Far more efficient than an LDO for large drops, at the cost of switching noise and more parts.

bus termination

Resistors at the ends of a bus to absorb reflections

On fast or long lines (CAN, RS-485, high-speed buses) a resistor matched to the line's characteristic impedance is placed at each end so signal energy is absorbed rather than reflected back as ringing. CAN uses ~120 Ω at both ends.

CAN dominant/recessive

CAN bus bit states: dominant (0) overrides recessive (1)

Recessive is the idle state held by the bus; a dominant bit actively drives CAN+ and CAN− apart, sourcing current through the terminators. Because dominant always wins on a shared wire, it enables collision-free bitwise arbitration.

characteristic impedance

The impedance a transmission line presents to a signal (e.g. 50 Ω, 120 Ω)

Set by the geometry and dielectric of a trace or cable, not its length. Matching the source and termination to this value prevents reflections; a CAN pair is ~120 Ω and most coax is 50 Ω.

Clarke transform

Maps three-phase quantities onto two stationary axes (α, β)

It collapses the three 120°-apart phase signals into an equivalent two-axis (αβ) stationary frame, simplifying three-phase math. It is the first step before the Park transform in field-oriented control.

CMRR

Common-mode rejection ratio: how well a differential amp ignores common-mode signals

CMRR is the ratio of differential gain to common-mode gain, often in dB. A high CMRR lets you recover a small differential signal riding on a large shared noise voltage, like EMI picked up equally by both wires.

common-mode voltage

The voltage both inputs share, relative to ground

For a differential pair it is the average of the two inputs, (V+ + V−)/2. Receivers and op-amps only tolerate a limited common-mode range, and a good design rejects this part while amplifying the difference.

DAQ

Data acquisition: sampling real-world signals into a computer

A DAQ system conditions sensor signals, digitizes them with ADCs, and timestamps them for logging or analysis. On an ESP32 the ADC plus a sample timer is a small DAQ front end.

decoupling capacitor

A cap next to a chip that supplies fast current spikes

Also called a bypass cap, it sits across the power pins to shunt switching noise to ground and provide instantaneous charge the supply can't deliver quickly enough. Place it as close to the IC power pins as possible.

deep sleep

ESP32 power mode that consumes microamps

In deep sleep, the CPU stops, RAM is lost (unless using RTC memory), and only RTC peripherals run. Wake sources include timer, GPIO, or touch.

differential signaling

Sending data as the difference between two complementary wires

The same signal is driven on two conductors in opposite polarity (e.g. CAN, RS-485, USB, Ethernet). Noise couples nearly equally into both wires as common mode, so the receiver subtracts it out, giving strong noise immunity.

dropout voltage

The minimum input-to-output difference a regulator needs to regulate

Below this headroom an LDO can no longer hold its output and it simply tracks the input minus dropout. A 3.3 V LDO with 200 mV dropout needs at least ~3.5 V in to stay in regulation.

duty cycle

Fraction of time the PWM signal is HIGH

Duty cycle controls average power: 25% duty means HIGH for 1/4 of each period.

EMC

Electromagnetic compatibility: coexisting without interference

A system's ability to function in its electromagnetic environment without emitting too much noise (emissions) or being upset by it (immunity). EMC compliance is required for most products to ship.

EMI

Electromagnetic interference: unwanted coupled electrical noise

Energy radiated or conducted from one circuit that disturbs another, from sources like switching supplies, fast edges, or external radio. Managed with shielding, filtering, good return paths, and slower edges.

ESL

Equivalent series inductance: a capacitor's internal inductance

The parasitic inductance of a real capacitor's leads and plates. ESL sets the self-resonant frequency above which the part stops looking capacitive, which is why small high-frequency caps are paired with bulk caps.

ESR

Equivalent series resistance: a capacitor's internal resistance

Real capacitors behave like an ideal cap in series with a small resistance. ESR limits how much ripple current a cap can absorb and causes self-heating; low-ESR caps are needed for switching-supply output filtering.

field-oriented control

Motor control that splits stator current into torque and flux parts

Also called vector control, FOC transforms the three-phase currents into two orthogonal components (one setting magnetic flux, one setting torque) so they can be regulated independently for smooth, efficient drive.

floating

An input with no defined HIGH/LOW state

Floating inputs pick up noise and randomly flip. Always use pull-ups or pull-downs.

FMEA

Failure Mode and Effects Analysis: list how a design can fail

A structured review of each component and function, recording its possible failure modes, their causes, and their effects on the system. It drives design changes and is often scored with a Risk Priority Number.

ground bounce

A momentary shift in the local ground reference during fast switching

When many outputs switch at once, the current spike through the inductance of the ground path develops a voltage, so the chip's ground briefly differs from the board ground. This can cause false logic levels and glitches.

ground loop

Two points meant to share a ground end up at different potentials

When current flows in the conductor joining two grounds, its voltage drop makes the two 'grounds' differ, injecting noise or hum. Common in audio and multi-board systems; fixed by single-point grounding or isolation.

HALT

Highly Accelerated Life Test: stress a product to find weak points

A reliability test that applies escalating temperature, vibration, and voltage extremes well beyond normal use to provoke failures fast. The goal is to expose design and process weaknesses, not to predict field life.

JTAG

A standard debug/test port for chips and boards (IEEE 1149.1)

A four-or-five-wire serial interface to an on-chip Test Access Port that reaches internal registers without touching the system buses. Used for boundary scan, flashing, and live debugging.

Kelvin (4-wire) sensing

Measuring resistance with separate force and sense wires

One pair of wires carries the test current and a second pair senses voltage right at the device, so lead and contact resistance drop out of the reading. Essential for accurately measuring very small resistances like shunts.

LDO

Low-dropout regulator: a linear regulator that works with little headroom

An LDO regulates output even when the input is only slightly above the target (small dropout voltage). It is quiet and simple but burns the voltage difference as heat, so it is inefficient when stepping down a lot.

LSB

Least significant bit: the smallest step a converter resolves

One LSB is the voltage represented by a single code change, equal to the full-scale range divided by 2^bits. It sets a converter's resolution; an n-bit ADC's quantization error is about ±½ LSB.

NACK

A no-acknowledge bit (SDA HIGH on the 9th clock)

In I²C, NACK often means 'no device responded' or 'stop sending me data'.

Ohm's Law

V = I × R (voltage equals current times resistance)

The fundamental relationship in DC circuits. If you know any two of voltage, current, or resistance, you can calculate the third.

open-drain

Outputs can pull LOW, but need pull-ups for HIGH

I²C uses open-drain so multiple devices can share a wire safely. No device actively drives HIGH; pull-up resistors do that.

Park transform

Rotates the αβ frame to align with the rotor (d, q axes)

It turns the stationary αβ quantities into a rotating direct/quadrature (dq) frame that spins with the rotor, so sinusoidal AC values become near-DC and easy to regulate with simple PI controllers.

PDN

Power distribution network: everything delivering power to the chips

The regulators, planes, traces, and decoupling caps that move clean, stable voltage from the source to each load. PDN design targets low impedance across frequency so switching loads don't sag or ring the rail.

power

P = V × I (watts)

Power is energy per unit time. In electronics, P = V × I. High power means heat: components have maximum power ratings.

power budget

Calculating total energy consumption over time

Sum (current × time) for each mode (active, sleep, transmit). Critical for battery-powered devices.

pull-up

A resistor that makes an input read HIGH by default

A pull-up (external or internal) prevents a GPIO input from floating. For a button-to-GND wiring, enable an internal pull-up or add ~10kΩ to 3.3V.

quantization

Rounding a continuous value into discrete steps

ADCs quantize voltages into integer codes; PWM duty also quantizes into timer steps.

quiescent current

The current a part draws just to stay powered, with no load

Often written Iq, this is the regulator's or chip's own housekeeping current. Low Iq is critical in battery designs where the device spends most of its life sleeping.

RC time constant

τ = R × C (how fast a capacitor charges/discharges)

After one time constant (τ), a capacitor charges to ~63% of the final voltage. After 5τ, it's essentially fully charged.

return path

The route current takes back to its source through ground

Every signal current must return to its source, usually through the ground plane directly under the trace at high frequency. A broken or detoured return path increases loop area, raising EMI and crosstalk.

rise time

Time for a signal to go from 10% to 90% of its final value

Measured on a rising edge, usually between the 10% and 90% points. Fast rise times carry high-frequency content, which drives ringing, reflections, and EMI on poorly terminated lines.

RPN

Risk Priority Number: FMEA score = severity × occurrence × detection

Each failure mode is rated 1–10 on how bad it is, how likely it is, and how hard it is to detect, then the three are multiplied. Higher RPN flags which failures to mitigate first.

slew rate

How fast a voltage can change, in volts per microsecond

The maximum rate of change an amplifier or driver output can produce (V/µs). Too low a slew rate distorts fast signals; deliberately slowing edges is also used to reduce EMI.

strapping pin

A GPIO that affects boot mode on reset

Some ESP32 pins are sampled on reset to decide boot configuration. External circuits (like buttons) can accidentally force a bad boot mode.

transceiver

A chip that both transmits and receives on a bus

It converts a controller's logic-level TX/RX signals into the bus's physical levels and back, such as a CAN or RS-485 transceiver driving a differential pair. It handles drive strength, common-mode range, and fault protection.

voltage divider

Two resistors in series create a fraction of the input voltage

V_out = V_in × (R2 / (R1 + R2)). Used for level shifting, sensor scaling, and battery monitoring.

Weibull distribution

A flexible failure-time distribution used in reliability

Its shape parameter k tells you the failure mode: k<1 is early-life (infant mortality), k=1 is constant random failure, and k>1 is wear-out. Fitting field data to it predicts how failure rate changes over time.