Biomedical Engineering Reference
In-Depth Information
FIgURE 7.5:
Data from neural recording in the rat motor cortex at a depth of 1.66 µm during implan-
tation surgery. Inset shows two distinct neurons recorded by single probe.
confirm the biocompatibility of the electrode material. However, because of the adaptability of the
fabrication process, other metals such as platinum may be readily incorporated.
7.2 aMPlIFICaTIoN
The next step in the signal processing chain is amplification. Because of the very small signal levels
(microvolts) the amplification needs to be done very close to the frontend. The design of the head-
stage, that is, the connector that links the electrodes and the cables to the amplifier is critical. Imped-
ance matching must be carefully controlled, and most designs use separate ground and reference.
The amplifiers have gains of 40-70 dB, a frequency response between 0.1 Hz and 10 kHz,
and are therefore AC coupled. One of the most important requirements is high common mode
rejection because of the large electrical artifacts normally present (60 Hz interference and other
electrical noises). In rack-mounted instrumentation, the amplifiers are well within the technol-
ogy envelope and several manufacturers provide excellent instruments (Tucker-Davis Technologies,
Plexon, Grass, Biosemi, Axon, Alpha-Omega). The difficulty is in portable designs. We present
briefly below an analog amplifier we have developed at the University of Florida (Harris).
7.2.1 Integrated Bioamplifier
The custom amplifier consists of two stages: a low-noise 40-dB preamplifier and a second-stage 40-
dB amplifier that were fabricated in the 0.6-µm AMI complementary metal oxide semiconductor
