Cirrus Logic AN300 REV1 - Manual (Page 10)

10 AN300REV1
AN300
Figures 13 and 14 illustrate the noise performance of the CS3001/2 amplifiers. Figure 13 illustrates the extreme
low-frequency noise performance of the CS3001/2. This plot is based upon a real measurement taken over an 18
hour period. Have you ever seen a data sheet for an operational amplifier from another vendor show a plot of noise
below 0.1 Hz? Unlikely, because 0.1 Hz is arbitrarily considered the point of transition between examining the
effects of 1/f noise versus the effects of offset drift due to temperature changes. This plot is possible for the
CS3001/2/11/12 series amplifiers from Cirrus Logic only because of the very low drift due to chopping along with
low-noise performance.
Figure 13. CS3001/02 Low-frequency Noise (Measured)
Figure 14 illustrates the noise behavior of the CS3001/2 as the frequency increases above 2 kHz. The CS3001/2
devices are designed to be used for low frequency (less than 2 kHz) applications. The CS3001/2 design achieves
a significant reduction in power consumption by lowering the operating current of the last amplifier stage. This com-
promise causes the noise in the device to rise at frequencies above 2 kHz. This noise can be removed by filtering.
Some delta-sigma A/D converters have digital filters that can remove the noise above 2 kHz.
Figure 14. CS3001/02 Wideband Noise