Phaselocke: Lock-In Amplifier
Measurement, Noise & the Lab arc, page 135 of 193. Back to The Pixelated Physics Universe
Who they are
Phaselocke has one line, and says it often: “Buried in noise. locked in anyway.”
Phaselocke is a character of the Measurement, Noise & the Lab arc: drawn in pixels, ruled by one piece of real physics, and never allowed to break it.
The physics
Lock-in detection multiplies the signal by a reference at fref and low-pass filters, recovering a signal buried far below broadband noise.
$$ \begin{gathered} V_{\text{out}} = \tfrac{1}{2} V_s V_r \cos\theta \end{gathered} $$
| Symbol | Meaning | SI unit |
|---|---|---|
| $V_{\text{out}}$ | low-pass filtered output | V^2 |
| $V_s$ | signal amplitude at f_ref | V |
| $V_r$ | reference amplitude | V |
| $\theta$ | phase difference between signal and reference | — |
Sources
Crossovers
Phaselocke meets Thermican (Bolometer Time Constant). Thermican's slow time constant limits how fast her bolometer can respond. Phaselocke chops the signal at a frequency she can follow and pulls it out of the drift with a lock-in.
Phaselocke meets Aliasyne (Nyquist Sampling Aliasing). Aliasyne warns that sampling below twice the highest frequency folds signals into false ones. Phaselocke's lock-in depends on careful filtering that keeps unwanted frequencies out of the band.
Phaselocke meets Flickermoth (1/f Pink Noise). Flickermoth's 1/f noise grows at low frequencies. Phaselocke dodges it by moving the signal up to a reference frequency where the noise is lower.
Wear the lore
Concept keywords: Lock-In Amplifier, Phaselocke, Measurement, Noise & the Lab, physics lore, Pixelated Physics