TDA7406T Datasheet, PDF (17/49 Pages) STMicroelectronics – CAR RADIO SIGNAL PROCESSOR

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 SA_out 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 SA_out.
Each analog output data is valid after the time t_SAdel.
A reset of the sample capacitors is induced whenever SA_clk remains high for the time t_intres. Note that a proper
reset requires the clock signal SA_clk 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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