CS5101A datasheet(27/40 Pages) CIRRUS

27 / 40 page

at high signal frequencies due to nonlinearities in

the internal MOS switches. Dynamic signals

cause ac current to flow through the switches

connecting the capacitor array to the analog input

pin in the track mode. Nonlinear on-resistance in

the switches causes a nonlinear voltage drop.

This effect worsens with increased signal fre-

quency and slew rate. This distortion is negligible

at signal levels below -10 dB of full-scale.

Noise

An A/D converter’s noise can be described like

that of any other analog component. However,

the converter’s output is in digital form so any

filtering of its noise must be performed in the

digital domain. Digitized samples of analog in-

puts are often considered individual, static snap-

shots in time with no uncertainty or noise. In

reality, the result of each conversion depends on

the analog input level and the instantaneous value

of noise sources in the ADC. If sequential sam-

ples from the ADC are treated as a "waveform",

simple filtering can be implemented in software

to improve noise performance with minimal proc-

essing overhead.

All analog circuitry in the CS5101A and

CS5102A is wideband in order to achieve fast

conversions and high throughput. Wideband

noise in the CS5101A and CS5102A integrates to

µV rms in unipolar mode (70 µV rms in bipo-

lar mode). This is approximately 1/2 LSB rms

with a 4.5V reference in both modes. Figure 21

Figure 18. CS5101A FFT (SSC Mode, 1-Channel)

Input Frequency (kHz)

-130

-120

-110

-100

-90

-80

-70

-60

-50

-40

-30

-20

-10

Signal Level

Reletive To

Full Scale

(dB)

Figure 17. CS5101A FFT (SSC Mode, 1-Channel)

Input Frequency (kHz)

-130

-120

-110

-100

-90

-80

-70

-60

-50

-40

-30

-20

-10

Signal Level

Relative to

Full Scale

(dB)

Input Frequency (kHz)

-130

-120

-110

-100

-90

-80

-70

-60

-50

-40

-30

-20

-10

Signal Level

Reletive To

Full Scale

(dB)

S/N+D: 92.01 dB

S/D: 101.8 dB

Figure 19. CS5102A FFT (SSC Mode, 1-Channel)

Input Frequency (kHz)

-130

-120

-110

-100

-90

-80

-70

-60

-50

-40

-30

-20

-10

Signal Level

Relative to

Full Scale

(dB)

Figure 20. CS5102A FFT (SSC Mode, 1-Channel)

S/(N+D): 91.06 dB

S/D: 100.5 dB

TA = 138 °C

S/(N+D): 91.71 dB

S/D: 101.6 dB

S/(N+D): 92.01 dB

S/D: 101.8 dB

S/(N+D): 92.00dB

S/D: 101.6 dB

TA = 138 °C

CS5101A CS5102A

DS45F2

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