The characterization report

Why one page

A datasheetDatasheet The manufacturer's document for a chip: pinout, limits, typical performance, and the reference circuit you should start from. Glossary entry is a characterizationCharacterization Measuring what your instrument actually does, such as its noise floor, bandwidth, and rejection, instead of assuming the datasheet. Related: Noise floorNoise floor What your instrument records when the input is shorted or connected to a perfectly quiet source; everything smaller than this is invisible to you. , PhantomPhantom A physical stand-in for tissue, such as saline gelatin with embedded wires, used to test an instrument against known signals. , Common-mode rejection ratio (CMRR)Common-mode rejection ratio (CMRR) How much better an amplifier responds to a difference between its inputs than to a signal shared by both, in decibels; 100 dB means 100,000 times. . Glossary entry report written by the manufacturer. Yours is the same thing, written by you, about the whole system: chip, board, cables, electrodesElectrode The conductor that turns ion currents in tissue into electron currents in a wire; its chemistry and contact quality set the noise you live with. Related: Silver/silver-chloride (Ag/AgCl)Silver/silver-chloride (Ag/AgCl) The standard electrode material for biopotentials, because its chemistry produces a stable, low-noise, low-drift interface with salty gel. , Electrode impedanceElectrode impedance How hard it is to push current through the skin-electrode contact, typically 5 to 50 kilohms with gel and megohms dry, higher at low frequencies. , Half-cell potentialHalf-cell potential The DC voltage that appears wherever a metal meets an electrolyte; two electrodes with different half-cell potentials produce an offset that can swamp the signal. . Glossary entry. It is one page because that is what anyone will read, and because if you cannot state what your instrument does in one page, you do not yet know. Every row is a number, the conditions under which you measured it, and a pointer to the plot.

The template

INSTRUMENT: 8-channel EEG amplifier, rev B          DATE: 2026-11-02   AUTHOR: ...
Configuration: ADS1299, gain 24, 250 SPS, internal reference, bias drive on,
               inputs via 2.2 kΩ series + touch-proof connectors, Ag/AgCl cups with Ten20.

Metric                       Value            Conditions / method                          Plot
Input-referred noise         0.92 µV RMS      inputs shorted at connector, 60 s, 0.5–40 Hz  fig1
Noise with electrodes        2.1 µV RMS       in phantom, dipoles off, 60 s, 0.5–40 Hz      fig1
Noise spectrum shape         1/f below 3 Hz   Welch, 4 s windows                             fig2
Bandwidth (−3 dB)            0.3 – 64 Hz      phantom dipole sweep, 10 µA                    fig3
Gain accuracy                +1.8 %           10 µA at 10 Hz vs. forward-model prediction    fig3
CMRR, bias drive off         78 dB            100 mV 60 Hz on phantom vs. reference          fig4
CMRR, bias drive on          104 dB           same                                           fig4
Crosstalk, adjacent channel  −68 dB           20 Hz on dipole 1, ch2 vs ch1                  fig5
Input range (linear)         ±180 mV          amplitude sweep to 1 % deviation               fig6
Sample drop rate             0 in 150,000     10 min, frame counter                          n/a
Battery life                 9.5 h            3×AA, streaming over Wi-Fi                     n/a
Known limitations: 1/f noise dominates below 2 Hz; CMRR falls to 84 dB at 180 Hz;
                   channel 6 shows 0.4 µV more noise than others (suspect input resistor).

Rules for each row

A number with units. “Low noise” is not a row. “0.92 µV RMS” is.

Conditions sufficient to repeat it. Bandwidth, duration, what the inputs were connected to, the gainGain How many times an amplifier multiplies its input; 1000× turns 50 microvolts into 50 millivolts, enough for an ADC to see. Related: Instrumentation amplifierInstrumentation amplifier A precision differential amplifier with very high input impedance and high CMRR, built from three op-amps and sold as a single chip such as the INA128 or AD8232. . Glossary entry and rate. Someone with your board and your notes should get your number.

A plot for every number that has a shape. Noise gets a trace and a spectrumSpectrum A plot of how much of a signal lives at each frequency. Related: Fast Fourier transform (FFT)Fast Fourier transform (FFT) The algorithm that breaks a stretch of signal into the sinusoids that would add up to it, giving amplitude and phase at each frequency. , Power spectral density (PSD)Power spectral density (PSD) The spectrum expressed as power per hertz, the standard way to quantify how strong alpha is. . Glossary entry. Bandwidth gets the sweep. CMRRCommon-mode rejection ratio (CMRR) How much better an amplifier responds to a difference between its inputs than to a signal shared by both, in decibels; 100 dB means 100,000 times. Related: Common-mode signalCommon-mode signal A voltage that appears equally on both inputs of a differential amplifier, such as 60 Hz hum picked up by the whole body. , Electrode impedanceElectrode impedance How hard it is to push current through the skin-electrode contact, typically 5 to 50 kilohms with gel and megohms dry, higher at low frequencies. . Glossary entry gets the injected and recorded spectra on one axis. Plots go on a second page or in an appendix; the first page stays one page.

Comparison to the spec. Where the datasheetDatasheet The manufacturer's document for a chip: pinout, limits, typical performance, and the reference circuit you should start from. Glossary entry claims a number, put it in a column and compare. Your CMRRCommon-mode rejection ratio (CMRR) How much better an amplifier responds to a difference between its inputs than to a signal shared by both, in decibels; 100 dB means 100,000 times. Related: Common-mode signalCommon-mode signal A voltage that appears equally on both inputs of a differential amplifier, such as 60 Hz hum picked up by the whole body. , Electrode impedanceElectrode impedance How hard it is to push current through the skin-electrode contact, typically 5 to 50 kilohms with gel and megohms dry, higher at low frequencies. . Glossary entry will be lower than the chip’s because the electrodesElectrode The conductor that turns ion currents in tissue into electron currents in a wire; its chemistry and contact quality set the noise you live with. Related: Silver/silver-chloride (Ag/AgCl)Silver/silver-chloride (Ag/AgCl) The standard electrode material for biopotentials, because its chemistry produces a stable, low-noise, low-drift interface with salty gel. , Electrode impedanceElectrode impedance How hard it is to push current through the skin-electrode contact, typically 5 to 50 kilohms with gel and megohms dry, higher at low frequencies. , Half-cell potentialHalf-cell potential The DC voltage that appears wherever a metal meets an electrolyte; two electrodes with different half-cell potentials produce an offset that can swamp the signal. . Glossary entry are in the loop; say so.

Known limitations, honestly. The row that impresses a reviewer is the one where you found something wrong and characterized it instead of hiding it.

What it is for

It is what you send a professor when you ask to join their lab, instead of “I’m interested in BCIBrain-computer interface (BCI) A system that turns measured brain activity into control of something outside the body, from a cursor to a wheelchair to a speech synthesizer. Related: DecoderDecoder The algorithm that maps neural signals to intended actions, such as a classifier or a Kalman filter. , Closed loopClosed loop A system in which the output feeds back to influence the input, such as a user adjusting their brain activity while watching the cursor it controls. . Glossary entry.” It is what you bring to Blackrock or Ripple when you ask for a tour. It is the verificationVerification Testing that the device meets its requirements; did you build what you specified. Related: ValidationValidation Testing that the device meets the user's need in real use; did you specify the right thing. . Glossary entry section of the mock design history file in Phase 5. It is the appendix of your first poster. And it is the habit that, more than any other, marks the difference between people who make things that work on the bench and people who make instruments.