ABSTRACT
The noise considered in this chapter provides one limitation to the precision of biomedical measurements. Other factors that limit resolution are the distortion caused by signal conditioning system nonlinearity and quantization in the analog-to-digital conversion (ADC) of input signals. The degree to which a biosignal is resolvable can be determined by the signal-to-noise ratio at the output of the signal conditioning system. The noise in this chapter is considered to arise in a circuit, measurement system, or electrode from completely random processes. Although any physical quantity can be "noisy,” this chapter will generally consider only completely random noise voltages and currents; these will be defined as being stationary (the physical process giving rise to the noise does not change with time) and having zero mean (zero additive dc components). An unwanted dc component accompanying a noise source in practice can be from an electrochemical EMF arising in a recording electrode or from amplifier dc offset voltage or bias current. The reduction of unwanted dc components will not be treated here.
