8

AN314REV1

AN314

Figure 7. 8-input, Single-ended, Multiple Input Range, Multiplexed System

The circuit shown in Figure 7 is similar to the differential circuit except there is no need to convert the single-ended

input signal to differential. As mentioned previously, there will be a loss of approximately 6 dB in noise performance

using the single-ended input device, since the full-scale input is half that of the differential device. As illustrated, not

every input may need a buffer and if the source impedance is very low, better performance may be obtained without

a buffer. In order to maintain DC accuracy, the series resistance in the unbuffered inputs needs to be kept very low.

The key in this configuration is to keep the impedance between the ACOM pin of the ADC and the source signal as

low as possible. Any current flowing in this return path will result in errors since there is no common-mode rejection

with a single-ended device.