CS5351 查看數據表（PDF） - Cirrus Logic

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CS5351

108 dB, 192 kHz, Multi-bit Audio A/D Converter

Cirrus Logic 

CS5351

4.4 Analog Connections

The analog modulator samples the input at 6.144 MHz. The digital filter will reject signals within the stop-

band of the filter. However, there is no rejection for input signals which are (n × 6.144 MHz) the digital pass-

band frequency, where n=0,1,2,...Refer to Figure 24 which shows the suggested filter that will attenuate any

noise energy at 6.144 MHz, in addition to providing the optimum source impedance for the modulators. The

use of capacitors which have a large voltage coefficient (such as general purpose ceramics) must be avoid-

ed since these can degrade signal linearity.

100 kΩ

100 kΩ

1 μF

100 kΩ

634 Ω

470 pF

C0G

-

91 Ω

+

2700 pF

C0G

100 kΩ

1 μF

-

+

1 μF

0.01 μF

+

-

91 Ω

470 pF

C0G

634 Ω

2700 pF

C0G

Figure 24. CS5351 Recommended Analog Input Buffer

CS5351

AINL

VQ1

VQ3

VQ2

AINR

4.5 High-Pass Filter and DC Offset Calibration

The operational amplifiers in the input circuitry driving the CS5351 may generate a small DC offset into the

A/D converter. The CS5351 includes a high pass filter after the decimator to remove any DC offset which

could result in recording a DC level, possibly yielding "clicks" when switching between devices in a multi-

channel system.

The high pass filter continuously subtracts a measure of the DC offset from the output of the decimation

filter. If the HPF pin is taken high during normal operation, the current value of the DC offset register is frozen

and this DC offset will continue to be subtracted from the conversion result. This feature makes it possible

to perform a system DC offset calibration by:

Running the CS5351 with the high pass filter enabled until the filter settles. See the Digital Filter Character-

istics for filter settling time.

Disabling the high pass filter and freezing the stored DC offset.

A system calibration performed in this way will eliminate offsets anywhere in the signal path between the

calibration point and the CS5351.

18

DS565F2

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