Low size, low power, and wearable bio-signal recording systems require acquisition front-ends with high common-mode rejection for interference suppression and adjustable gain to provide an optimum signal level to a cascading analog-to-digital stage. This thesis presents the realization of microcontroller operated double-differential (DD) recording setup with automatic gain control (AGC) and automatic balance control, which can adjust the magnitude of recorded bio-potential signal to a target level and reject common-mode interference for full-bandwidth recording without filtering. Microcontroller code realizes the automatic control method of gain and balance adjustment by detecting, computing, and varying parameters to set timing clock pulses, which determine the gain magnitude and balance state. The automatic balance control compensates for imbalance in electrode interface impedance. The double-differential amplifier is implemented using two integrated variable gain amplifiers (ASIC) and one adder. Measured results of the variable gain amplifiers fabricated in 0.35 £gm CMOS technology show an input spot noise of 169 nV/¡ÔHz, a NEF below 10, and a circuit active area of 0.017 mm2 with a power consumption of 1.44 £gW. Measured results of the double-differential amplifier setup confirm interference suppression of 25.7 dB, tunable gain range of 39.6 dB, and 239 nV/¡ÔHz noise assuming ¡Ó10% interface mismatch. Practical measured examples incorporating the chips confirm gain control suitable for bio-potential recording and interference suppression in a balanced DD arrangement for electrocardiogram and electromyogram recording.

A well documented laboratory setup, leech preparation process, and bio-potential data recording process are needed. Repeatability and quality data recordings are essential and thus dictate the requirements of the laboratory setup and processes listed above. Advances in technology have both helped and hindered this development. While very precise equipment is required to record the low voltage bio-potentials, noisy electronic equipment and wires surrounding the work area provide high levels of interference. Proper laboratory setup and data recording processes, however, limit the unwanted interference. Quality data can only be recorded from a properly handled and prepared leech subject. Proper setup and procedures result in quality recordings which lend a clean signal for furthering the understanding of nerve functionality. The electrophysiology lab at California Polytechnic State University in San Luis Obispo is an example of a proven lab setup for high quality signal capture.