CS47L24 datasheet(68/256 Pages) CIRRUS

68 / 256 page

CS47L24

Rev 4.1

LOW PASS / HIGH PASS DIGITAL FILTER (LHPF)

The digital core provides four Low Pass Filter (LPF) / High Pass Filter (HPF) processing blocks as illustrated in Figure 20.

A 4-input mixer is associated with each filter. The 4 input sources are selectable in each case, and independent volume

control is provided for each path. Each Low/High Pass Filter (LHPF) block supports 1 output.

The Low Pass Filter / High Pass Filter can be used to remove unwanted ‘out of band’ noise from a signal path. Each filter

can be configured either as a Low Pass filter or High Pass filter.

CS47L24 supports 4 LHPF blocks, ie. n = 1, 2, 3 or 4

LHPFnMIX_VOL2

LHPFnMIX_VOL3

LHPFnMIX_VOL4

LHPFnMIX_VOL1

LHPFnMIX_SRC1

LHPFnMIX_SRC3

LHPFnMIX_SRC4

LHPFnMIX_SRC2

LHPF1 (60h)

LHPF2 (61h)

LHPF3 (62h)

LHPF4 (63h)

LHPF

Low-Pass filter (LPF) /

High-Pass filter (HPF)

Figure 20 Digital Core LPF/HPF Blocks

The LHPF1, LHPF2, LHPF3 and LHPF4 mixer control registers (see Figure 20) are located at register addresses R2304

(900h) through to R2335 (91Fh).

The full list of digital mixer control registers is provided in the “Register Map” section (Register R1600 through to R3000).

Generic register definitions are provided in Table 7.

The *_SRCn registers select the input source(s) for the respective LHPF processing blocks. Note that the selected input

source(s) must be configured for the same sample rate as the LHPF to which they are connected. Sample rate

conversion functions are available to support flexible interconnectivity -

see “Asynchronous Sample Rate Converter

(ASRC)

” and “Isochronous Sample Rate Converter (ISRC)”.

The bracketed numbers in Figure 20,

e.g.,”(60h)” indicate the corresponding *_SRCn register setting for selection of that

signal as an input to another digital core function.

The sample rate for the LHPF function is configured using the FX_RATE register - see Table 21. Note that the EQ, DRC

and LHPF functions must all be configured for the same sample rate.

The LHPF function supports audio sample rates in the range 8kHz to 192kHz. When the DRC is enabled, the maximum

sample rate for the EQ, DRC and LHPF functions is 96kHz.

Sample rate conversion is required when routing the LHPF signal paths to any signal chain that is asynchronous and/or

configured for a different sample rate.

The control registers associated with the LHPF functions are described in Table 15.

The cut-off frequencies for the LHPF blocks are set using the coefficients held in registers R3777, R3781, R3785 and

R3789 for LHPF1, LHPF2, LHPF3 and LHPF4 respectively. These coefficients are derived using tools provided in Cirrus

Logic

’s WISCE™ evaluation board control software; please contact your local Cirrus Logic representative for more

details.

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