A low-noise optically isolated preamplifier for use with extracellular microelectrodes

Circuit Models and Experimental Noise Measurements of Micropipette Amplifiers for Extracellular Neural Recordings from Live Animals

“…This model is based on previous studies which examine the various physical phenomena attributed to noise generated in extracellular recording [8, 13, 19, 20, 49–56]. Our goal is to provide a unified yet simple mathematical model to help understand the important noise factors for neural recordings.…”

“…Z p is the equivalent impedance between the amplifier input and power line. For this reason, the amplifier front-end should be carefully designed to eliminate any electronic ground loops [8, 13] to avoid coupling environmental noise to the amplifier. Thus, in our model the impedance of Z p is assumed to be larger than Z in   ( Z p ≫ Z in ).…”

“…However, these models are largely based on the use of metal electrodes, such as tungsten, platinum, or titanium nitride electrodes, not glass micropipettes. Metal electrodes generally have better noise performance than glass micropipette electrodes [13, 19, 20]. For example, Millar and Barnett [13] reported that there is 65  μ V peak-to-peak thermal noise generated from a 1 MΩ glass micropipette over a recording frequency range between 100 Hz to 8 kHz, while a tungsten electrode in the same condition usually shows a noise level of ~20–50  μ V peak-to-peak.…”

“…Metal electrodes generally have better noise performance than glass micropipette electrodes [13, 19, 20]. For example, Millar and Barnett [13] reported that there is 65  μ V peak-to-peak thermal noise generated from a 1 MΩ glass micropipette over a recording frequency range between 100 Hz to 8 kHz, while a tungsten electrode in the same condition usually shows a noise level of ~20–50  μ V peak-to-peak. The reason that noise generated from a metal electrode is less than that of a glass micropipette is because the impedance of a metal electrode is largely capacitive [21], resulting in a smaller real component (resistance) to generate thermal noise.…”

“…For example, most of the studies [10–12, 14–18] only described intrinsic noise generated by the amplifiers themselves. Chae et al [9], Budai [8] and Millar and Barnett [13] discussed the additional noise of power-line interference but noise of biological origins and noise generated from electrodes were not included in their models. Yang et al [19] and Lopez et al [20] included both biological and electrode noise but their models are for metal electrodes only.…”