PCM1865DBT datasheet(39/115 Pages) TI

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HPF

LPF

HPF

Decimation

Filter

DSP#1

DSP#2

Energysense Loss of

Signal Flag

SGIDET _CH_ Mode[7 :0]

Signal Resume /

Present Flag

Control Voltage

Change Flag

Main ADC

Secondary

ADC

LOSS Level

RESUME Level

PCM1861, PCM1863, PCM1865

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SLAS831C – MARCH 2014 – REVISED AUGUST 2014

Figure 34. Dual Thresholds for Energysense

As both thresholds are DSP based, their coefficients are stored in virtual coefficient space that is programmed

through the device register map.

For example, to change the resume threshold value to –30dB (0x040C37):

Write 0x00 0x01 ; # change to register page 1

Write 0x02 0x2D ; # write the memory address of resume threshold

Write 0x04 0x04 ; # bit[23:15]

Write 0x05 0x0C ; # bit[15:8]

Write 0x06 0x37 ; # bit[7:0]

Write 0x01 0x01 ; # execute write operation

8.14.2.5 Frequency Response of the Secondary ADC

The natural response of the secondary ADC is not flat by frequency. However, the frequency response can be

flattened, so that all frequencies are equally sensitive to the energystar detector by modifying the LPF/HPF

biquads in the DSP.

An example of the code required is shown in Table 16.

8.14.3 Programming Various Coefficients for Energysense

Programming the DSP coefficients for the Energysense secondary ADC is done through the indirect virtual

programming registers in Page1. The Low Pass Filter (LPF) and High Pass filter (HPF) coefficients can be

written to flatten out the frequency response, as well as the Energysense Loss and Resume thresholds. Visually,

one can imagine the DSP flow as shown in Figure 35.

Figure 35. Energysense process flow

To flatten out the response of the secondary ADC, so that all frequencies are detected evenly, the following

biquads should be written to the virtual DSP memory, using the techniques discussed in Programming DSP

Coefficients.

Table 16. Secondary ADC Biquad Coefficients at 48kHz

Sampling

Coefficient

Virtual RAM Address

LPF_B0:

0x20

LPF_B1:

0x21

LPF_B2:

0x22

LPF_A1:

0x23

LPF_A2:

0x24

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PCM1865DBT Datasheet(PDF) 39 Page - Texas Instruments

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