Datasheet

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Default Bass-Boost Transfer Function 48 kHz Mode

1 10 100 1000 10000 100000

Frequency (Hz)

–0.5

–1

–1.5

–2

–2.5

–3

–3.5

Gain (dB)

TSC2301

SLAS371D – SEPTEMBER 2002 – REVISED AUGUST 2004

N0 = N3 = 27618 D1 = D4 = 32130

N1 = N4 = -27033 D2 = D5 = -31505

N2 = N5 = 26461

which implements the bass-boost transfer function shown in Figure 77 , having a 3-dB attenuation for signals

above approximately 150 Hz when operating at a 48-kHz sampling rate. All coefficients are represented by 16-bit

twos complement integers with values ranging from -32768 to 32767.

Figure 77. Transfer Function of Default Bass-Boost Filter Coefficients at 48-kHz Sampling Rate

Audio ADC

The audio ADC consists of a 4th order multi-bit analog delta-sigma modulator, followed by a digital decimation

filter. The digital output data is then passed to the bus interface for transmission back to the CPU.

The analog modulator is a fully differential switched-capacitor design with multi-bit quantizer and dynamic

element matching to avoid mismatch errors. The modulator operates at an oversampling ratio of 128 for all

sample rates. The input to the ADC is filtered by a single-pole analog filter with -3-dB point at approximately 500

kHz for antialiasing. This analog filter uses a single off-chip 1 nF cap per ADC (at the AFILT pins) and on-chip

resistor.

The digital decimation filter block includes a high-pass IIR filter for the purpose of removing any dc or

sub-audio-frequency component from the signal. Since such a low frequency filter can have significant settling

time, the filter has an adjustable cutoff frequency, in order to allow the host to set a faster settling time initially,

then later switch it back to a level that does not affect the audio band. The settings for this high-pass filter are:

HPF -3-dB frequency: 0.000019 Fs (0.912 Hz at Fs = 48 kHz)

0.000078 Fs (3.744 Hz at Fs = 48 kHz)

0.1 Fs (4.8 kHz at Fs = 48 kHz)

The filter block provides an audio passband ripple of +/-0.03 dB over a passband from 0 Hz to 0.454 sampling

frequency (Fs), and 70-dB minimum stopband attenuation from 0.548 Fs to 64 Fs.