CS42448 datasheet(29/64 Pages) CIRRUS

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DS648F2

CS42448

4.3.5

Line-Level Outputs and Filtering

The CS42448 contains on-chip buffer amplifiers capable of producing line-level differential as well as sin-

gle-ended outputs on AOUT1-AOUT8. These amplifiers are biased to a quiescent DC level of approxi-

mately VQ.

The delta-sigma conversion process produces high-frequency noise beyond the audio passband, most of

which is removed by the on-chip analog filters. The remaining out-of-band noise can be attenuated using

an off-chip low-pass filter.

See “DAC Output Filter” on page 56 for recommended output filter. The active filter configuration accounts

for the normally differing AC loads on the AOUTx+ and AOUTx- differential output pins. Also shown is a

passive filter configuration which minimizes costs and the number of components.

Figure 13 shows the full-scale analog output levels. All outputs are internally biased to VQ, approximately

VA/2.

4.3.6

Digital Volume Control

Each DAC’s output level is controlled via the Volume Control registers operating over the range of 0 to

-127.5 dB attenuation with 0.5 dB resolution. See “AOUTX Volume Control (Addresses 08h- 0Fh)” on

page 49. Volume control changes are programmable to ramp in increments of 0.125 dB at the rate con-

trolled by the SZC[1:0] bits in the Digital Volume Control register. See “Transition Control (Address 06h)”

on page 47.

Each output can be independently muted via mute control bits in the register “DAC Channel Mute (Ad-

dress 07h)” on page 49. When enabled, each AOUTx_MUTE bit attenuates the corresponding DAC to its

maximum value (-127.5 dB). When the AOUTx_MUTE bit is disabled, the corresponding DAC returns to

the attenuation level set in the Volume Control register. The attenuation is ramped up and down at the

rate specified by the SZC[1:0] bits.

4.3.7

De-Emphasis Filter

The CS42448 includes on-chip digital de-emphasis optimized for a sample rate of 44.1 kHz. The filter re-

sponse is shown in Figure 14. The de-emphasis feature is included to accommodate audio recordings

that utilize 50/15

μs pre-emphasis equalization as a means of noise reduction.

AOUTx+

AOUTx-

Full-Scale Differential Output Level =

(AOUTx+) - (AOUTx-) = 6.5 VPP = 2.3 VRMS

4.125 V

2.5 V

0.875 V

5.0 V

4.125 V

2.5 V

0.875 V

Figure 13. Full-Scale Output

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