TAS3103ADBT datasheet(114/154 Pages) TI2

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3−51

When updating multiple TAS3103As with dither seeds, timing should be taken into account. The recommended seed

update process is to load all TAS3103As with their seed values in less time than the minimum LFSR cycle time of

496.5 ms, and use the same set of seeds for all TAS3103As. Each TAS3103A immediately begins running, starting

at the state set by the new seed, on receiving the new seed. The sequential delivery, in time, of the seeds to the

multiple TAS3103As ensures that the TAS3103As do not all start with their new seeds at the same time, and the

completion of the process in less than 496.5 ms ensures that previously programmed TAS3103As are not repeating

the cycle at the same time that another TAS3103A is being programmed with the same seed set—causing correlation

between the dither data streams of the two TAS3103As.

CAUTION: The state of the digital audio processor may prevent the loading of a new

I2C-commanded dither seed value. Anytime a new seed is loaded into the TAS3103A via

an I2C write transaction to address 0xC7, it must be followed by an I2C read transaction

to address 0xC7 to verify that the new seed value was accepted. If the new seed was not

accepted, the write-read sequence must be repeated.

3.9.2

Dither Mix Options

In Figure 3−31, it is seen that the two LFSRs are logically combined to produce a triangular probability distribution.

This distribution is then sampled at six different points in time by the DAP processing clock to create six statistically

independent data streams. Sampling the LSFR outputs at different points in time within an audio sample period

(1/LRCLK) ensures that the six dither data streams are uncorrelated. The six uncorrelated dither data streams are

then routed through mixers. Each pair of mixer outputs is then applied to a summation block. It is noted in Figure 3−31

that each of the three mixer pairs has the same set of coefficients (set by I2C subaddress 0xC6). If the coefficients

for both mixers are set to 1, a quadratic distribution is obtained. If either coefficient is set to 0, a triangular distribution

is obtained. If both coefficients are set to 0, dither is disabled.

3.9.3

Dither Gain Mixers

Figure 3−31 shows the peak magnitude of the triangular distribution to be

±16 in the 48-bit DAP word (25.23 format).

The peak magnitude of the quadratic dither data is twice this, or

±32. Figure 3−32 shows the position of this peak

magnitude value in reference to the DAP 48-bit data word. Table 3−8 lists the mixer gains required to position the

dither data stream at the LSB of the output data word for different data sample word sizes.

Table 3−8. Mixer Gain Setting for LSB Dither Data Insertion

DISTRIBUTION

MIXER GAIN COEFFICIENT

DISTRIBUTION

32-BIT SAMPLE

24-BIT SAMPLE

20-BIT SAMPLE

18-BIT SAMPLE

16-BIT SAMPLE

Triangular

2−19

2−11

2−7

2−5

2−3

Quadratic

2−20

2−12

2−8

2−6

2−4

TAS3103ADBT Datasheet(PDF) 114 Page - Texas Instruments

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