4.1 Requirements for A-D converters

The primary purpose for the analog signal conditioning circuitry is to modify the sensor output into a form that can be optimally converted to a discrete time digital data stream by the data acquisition system. Some important input requirements of most data acquisition systems are:

1. The input signal must be a voltage waveform. The process of converting the sensor output to a voltage can also be used to reduce unwanted signals, i.e., noise.
2. The dynamic range of the input signal should be at or near the dynamic range of the data acquisition system (usually equal to the voltage reference level, Vref, or 2*Vref). This is important in maximizing the resolution of the analog to digital converter (ADC).
3. The source impedance, , of the input signal should be low enough so that changes in the input impedance, , of the data acquisition system do not affect the input signal.
4. The bandwidth of the input signal must be limited to less than half of the sampling rate of the analog to digital conversion.