Datasheet

-1

C1 C2 C3 C4

LM49370

SNAS356D –FEBRUARY 2007–REVISED MARCH 2012

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DAC PATH COMPENSATION FIR CONFIGURATION REGISTERS

To allow for compensation of roll off in the DAC and analog filter sections an FIR compensation filter is applied to

the DAC input data at the original sample rate. Since the DAC can operate at different over sampling ratios the

FIR compensation filter is programmable. By default the filter applies approx 2dB of compensation at 20kHz. 5

taps is sufficient to allow passband equalization and ripple cancellation to around +/0.01dB.

The filter can also be used for precise digital gain and simple tone controls although a DSP or CPU should be

used for more powerful tone control if required. As the FIR filter must always be phase linear, the coefficients are

symmetrical. Coefficients C0, C1, and C2 are programmable, C3 is equal to C1 and C4 is equal to C0. The

maximum power of this filter must not exceed that of the examples given below:

Figure 24. FIR Consumption Filter Taps

Sample Rate DAC_MODE C0 C1 C2 C3 C4

48kHz 00 334 –2291 26984 –2291 343

48kHz 01 61 –371 25699 –371 61

For DAC_MODE = '00 and '01', the defaults should be sufficient; but for DAC_MODE = '10' and '11', care should

be taken to ensure the widest bandwidth is available without requiring such a large attenuation at DC that inband

noise becomes audible.

Table 39. Compensation Filter C0 LSBs (0x20h)

Bits Field Description

7:0 C0_LSB Bits 7:0 of C0[15:0]

Table 40. Compensation Filter C0 MSBs (0x21h)

Bits Field Description

7:0 C0_MSB Bits 15:8 of C0[15:0]

Table 41. Compensation Filter C1 LSBs (0x22h)

Bits Field Description

7:0 C1_LSB Bits 7:0 of C1[15:0]

Table 42. Compensation Filter C1 MSBs (0x23h)

Bits Field Description

7:0 C1_MSB Bits 15:8 of C1[15:0]

Table 43. Compensation Filter C2 LSBs (0x24h)

Bits Field Description

7:0 C2_LSB Bits 7:0 of C2[15:0]

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