Cirrus Logic AN314 - Manual (Page 5)

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