CS5321 datasheet(22/38 Pages) CIRRUS

22 / 38 page

CS5320/21/22

DS454PP1

2.8 Performance

Figure 22, 23 and 24 illustrate the spectral perfor-

mance of the CS5321/22 and CS5320/22 chipsets

when operating from a 1.024 MHz master clock.

Ten 1024 point FFTs were averaged to produce the

plots.

Figure 22 illustrates the chip set with a 100 Hz,

-20 dB input signal. The sample rate was set at 1

kHz. Dynamic range is 122 dB.

The dynamic range calculated by the test soft-ware

is reduced somewhat in Figures 23 and 24 because

of jitter in the signal test oscillator. Jitter in the

100 Hz signal source is interpreted by the signal

processing software to be increased noise.

The choice of master clock frequency will affect

performance. The CS5320/21 will exhibit the best

Signal/ Distortion performance with slower modu-

lator sampling clock rates as slower sample rates

allow more time for amplifier settling.

For lowest offset drift, the CS5320/21 should be

operated with MCLK = 1.024 MHz and HBR = 1.

Slower modulator sampling clock rates will exhibit

more offset drift. Changing MCLK to 512 kHz

(HBR = 1) or changing HBR to zero (MCLK =

1.024 MHz) will cause the drift rate to double. Off-

set drift is not linear over temperature so it is diffi-

cult to specify an exact drift rate. Offset drift

characteristics vary from part to part and will vary

as the power supply voltages vary. Therefore, if the

CS5320/21 is to be used in precision dc measure-

ment applications where offset drift is to be mini-

mized, the power supplies should be well

regulated. The CS5320/21 will exhibit about

6 ppm/°C of offset drift with MCLK = 1 and HBR

= 1.

Gain drift of the CS5320/21 itself is about

5 ppm/°C and is not affected by either modulator

sample rate or by power supply variation.

Figure 22. 1024 Point FFT Plot with -20 dB Input, 100

Hz Input, ten averages

Dynamic Range = 122.0 dB

HBR = 1

OFST = 0

LPWR = 0

500

-20

-40

-60

-80

-100

-120

-140

-160

-180

Figure 23. 1024 Point FFT Plot with Full Scale Input,

100 Hz Input, HBR = 1, ten averages

S/D = 116.0 dB

S/N = 118.4 dB

S/N+D = 114.2 dB

HBR = 1

OFST = 0

LPWR = 0

500

-20

-40

-60

-80

-100

-120

-140

-160

-180

see text

Figure 24. 1024 Point FFT Plot with Full Scale Input,

100 Hz Input, HBR = 0, ten averages

500

-20

-40

-60

-80

-100

-120

-140

-160

-180

S/D = 122.7 dB

S/N = 117.1 dB

S/N+D = 116.4 dB

HBR = 0

OFST = 0

LPWR = 0

see text

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