Table 1.
Noise contributions of the photodiode dark current, the integrated op−amp input noise, the free op−amp input noise, and Johnson noise from feedback resistors. The addition of the noises in quadrature predicts the total instrument noise, 5.67 μV. After instrument noise, the RMS noise contributions of illumination and physiological sources are tabulated in−vitro (lobster) and in−vivo (rat) and compared to the peak amplitudes of the stimulus−evoked optical changes. The standard errors for these measurements are large due to variability of signal strength and illumination intensity from trial to trial, but values give the reader a general idea of each source’s noise generation.
| Noise source | RMS Contribution (Δf = 500Hz), μV | Quantity in Circuit | ||
|---|---|---|---|---|
| PD Op amp (UDT−555UV), Input Noise Voltage | 0.45 | 1 | ||
| PD (UDT−555UV/LN), Dark Current Noise | 0.91 | 1 | ||
| Op amp (TL074), Input Noise Voltage | 4.00 | 2 | ||
| 1 Mohm Resistor Johnson Noise | 2.88 | 4 | ||
| Total Expected Instrument Noise in Quadrature | 5.67 μV | |||
| Measured Instrument Noise | 4.53 μV | |||
| Noise Source | LED | LD | ||
| Lobster, In−vitro | μV | dI/I × 10−4 | μV | dI/I × 10−4 |
| Emitter (shot, speckle) RMS Noise | 114.1 | 0.70 | 190.0 | 9.55 |
| Peak Signal Size In−vitro | 128.6 ± 34.2 | 1.15 ± 0.34 | 48.1 ± 12.7 | 1.83 ± 0.46 |
| Rat, In−vivo | μV | dI/I × 10−4 | μV | dI/I × 10−4 |
| Emitter (shot, speckle) RMS Noise | 77.4 ± 22.0 | 0.64 ± 0.17 | 225.5 ± 111.5 | 3.51 ± 0.91 |
| Cardiac RMS Noise (3Hz) | 215.0 ± 72.2 | 1.82 ± 0.60 | 106.6 ± 48.5 | 1.72 ± 0.64 |
| Respiration RMS Noise (1Hz) | 182.1 ± 3.6 | 1.55 ± 0.02 | 56.5 ± 6.0 | 1.08 ± 0.08 |
| Mayer Waves RMS Noise (0.0 to 0.4Hz) | 616.8 ± 401.0 | 5.22 ± 3.37 | 550.3 ± 482.2 | 8.26 ± 7.19 |
| Total Noise Measured In−vivo | 824.0 ± 325.8 | 6.98 ± 2.72 | 680.7 ± 446.0 | 10.7 ± 6.2 |
| Peak Signal Size In−vivo | 381.7 ± 262.1 | 3.35 ± 2.19 | 162.3 ± 64.7 | 2.97 ± 0.66 |