The following points are worth noting:

1. The larger the number of bits, the better is the resolution. However this must be traded for a higher cost and usually a lower throughput for the system.

2. In analog to digital conversion, the output will be a digital code which may be a straight-forward binary representation of the signal, i.e., a Binary Code(BC), or it may be a Binary Coded Decimal (BCD). Since the conversion of a decimal number of BCD form is much easier, the BCD code is often used. In BCD code a decimal number such as 999 will be represented as 1001 1001 1001. For unipolar magnitude (signals which do not oscillate beween positive and negative valuees) only the magnitude needs to be converted. For bipolar signals (which oscillate between positive and negative), the sign of the signal also needs to be converted. The leading digit of the digital code is meant for this purpose. The resolution of conversion itself is specified in terms of bits (a binary digit of 0 or 1). For instance, 12-bit resolution with BCD digital code implies approximately 11000 accuracy of conversion.

The circuit that accomplishes AD conversion is usually preceded by a sample-and-hold (SH) circuit. In a SH circuit the analog voltage is sampled for a duration called the acquisition time that corresponds roughly to the reciprocal of the sampling frequency. At the end of the acquisition time the circuit status changes from `sample' to `hold' and the analog voltage corresponding to the latest instant of time is stored as voltage drop across a capacitor. In practice, the SH circuit can slow down data acquisition owing to the need for a finite time for S-H transition. This time is called aperture time. The reverse transition H-S once again corresponds to the acquisition time. The capacitor response to being charged can be controlled by the current capability of the amplifier driving it. The action of the AD converter (ADC) comes into play when the SH circuit is in the `hold' state.