Home medical equipment becomes increasingly popular as VLSI fabrication technology advances. However, there are two important factors for realizing a miniaturized biochip: low noise [1] and low power. Firstly, physiological signals are very susceptible to interference while the amplitude of the signal is only a few millivolts or less. If the circuit cannot reject noise effectively, it is hard to amplify the signal and obtain the output voltage of the recording system accurately. Secondly, it is not convenient to replace the batteries frequently when using the portable measurement instrument for the patients. This thesis is focused on the measurement of physiological signals, such as electrocardiography (ECG) [2], electroneurogram (ENG) [3] and electromyography (EMG) [4] , and designing an all-in-one recording system to measure the different physiological signals in a chip. For this purpose, a programmable multi-parameter system for recording of the wide range of physiological signals is designed. The system provides two types of input transconductance stages, BiCMOS and CMOS. BiCMOS amplifiers provide high gain , low noise [5] and low offset voltage suitable for the small amplitude of the physiological signal. On the other hand, CMOS amplifiers provide practically infinite input impedance and ultra-low leakage current. The system also provides three selectable amplifier modes: (a) double-differential amplifier, (b) single-differential amplifier in channel 1, (c) single-differential amplifier in channel 2. The double-differential amplifier provides a high common-mode rejection and adjustable gain for each channel to further reduce common-mode interference. The single-differential amplifier (channel 1 or channel 2) in the recording system are also accessible as differential-input and single-ended output channels. Moreover, the system provides an offset compensation structure to prevent the amplifier from exceeding the input range. The offset compensation system can selectively be turned off to reduce the power consumption.

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.