TABLE OF CONTENTS Often the choice of the data converter is the cornerstone of the entire design. As we have seen in the previous sections, a converter can have many specifications. Now that we have gone over what those specifications mean and how to read a data sheet we are ready to proceed to the next step. How, then, do you determine which converter best suits your needs?
The most obvious parameters that we may need to specify the converter are the resolution and sample rate. Remember that the resolution of converter and the accuracy may not be the same. Quite often it is really the accuracy that is required.
For ADCs when we think of sample rate, we generally mean the maximum frequency. However, when the sample rate is reduced, the hold time requirements of the hold capacitors in the SHA section of the ADC increase proportionally. This can lead to errors if the sample rate is slow enough for the droop rate of the SHA to allow the sampled voltage to decay till it is out of the error band before the next sample period. While the droop rate of ADCs with internal SHAs is typically not specified, a minimum sample rate will be. This effect is dependent on the architecture of the ADC. Successive approximation ADCs rarely have this problem but pipelined architectures often do.
How the ADC is to be used may also effect the part selection. Pipelined ADCs and
