TDA7406T datasheet(17/49 Pages) STMICROELECTRONICS

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TDA7406T

2.8 Spectrum analyzer

A fully integrated seven band spectrum analyzer with programmable quality factor is present in the IC (Figure

13).

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 SA clk 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 13 shows the block diagram and Figure

14 illustrates the read cycle timing of the spectrum analyzer.

The spectrum analyzer minimum repeat time is 50ms.

2.8.1 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.

Figure 13. Spectrum analyzer block diagram

Figure 14. Timing spectrum analyzer

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