TDA7406 Datasheet, PDF (24/64 Pages) STMicroelectronics – Car radio signal processor

Description of the audioprocessor part
TDA7406
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
0.0
-10.0
-20.0
dB
-30.0
-40.0
-50.0
10.0
100.0
1.0K
Hz
10.0K
4.8
4.8.1
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 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 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.
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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