AN314REV1

5

AN314

of approximately 6 dB in the full-scale signal-to-noise ratio. This is because the full-scale input range of the differ-

ential input devices is twice that of the single ended devices. For example the CS5560/70/80 has a differential input

range of 8.192 volts (±4.096) while the CS5561/71/81 has a full-scale input range of 4.096 volts (±2.048). For an

equivalent internal noise, this means the full-scale input-to-noise ratio improves by 6 dB when using the differential

input devices. Of course, in order to take advantage of the differential device, the signal being converted needs to

be a true differential signal that utilizes the full-scale range. Otherwise, a single-ended-to-differential conversion cir-

cuit would need to be designed using a low-noise op-amp such as illustrated in Figure 5.

Figure 5. Single-ended-to-differential Conversion Circuit

If the decision is made to use a differential input ADC then the MUX will need to be a dual-pole device. Otherwise,

for simpler implementations with less stringent noise performance requirements, a single-ended input device can

be used with a single-pole MUX.

±10.107 V

Single

Ended

Input

±4.096 V

Differential

Output

½ CS3004

20k

88.7k

20k

20k

½ CS3004

+

-

+

-

10k