TDA7406 datasheet(24/64 Pages) STMICROELECTRONICS

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Description of the audioprocessor part

TDA7406

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cutoff frequencies are not equal but shifted by the factor 1.125 to get a flat frequency

response (see Figure 14).

Figure 14.

Subwoofer Application with Lowpass @ 80/120/160Hz and HighPass @

90/135/180Hz

4.8

Spectrum analyzer

A fully integrated seven band spectrum analyzer with programmable quality factor is present

in the IC (Figure 15).

The spectrum analyzer consists of seven band pass filters with a rectifier and sample

capacitor which stores the maximum peak signal level since the last read cycle. This peak

signal level can be read by a microprocessor at the SAout pin. To allow easy interfacing to a

microprocessor analog port, the output voltage at this pin is referred to device ground.

The microprocessor starts a read cycle when there is a clock edge going negative at the

SAclk input. On the following positive clock edges, the peak signal level for the band pass

filters is subsequently switched to SAout. Each analog output data is valid after the time

tSAdel.

A reset of the sample capacitors is induced whenever SAclk remains high for the time tintres.

Note that a proper reset requires the clock signal SAclk to be held at high potential. Figure 15

shows the block diagram and Figure 16 illustrates the read cycle timing of the spectrum

analyzer.

The spectrum analyzer minimum repeat time is 50ms.

4.8.1

Spectrum Analyzer Filters

Each filter is realized as a switched capacitor with a 2nd order frequency response. The

center frequency of the filter stages are: 62,157, 396, 1K, 2.51K, 6.34k and 16kHz. It is

possible to choose between two different filter quality factors: 1.8 and 3.5.

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