TSC2101_07 Datasheet, PDF (25/93 Pages) Texas Instruments – AUDIO CODEC WITH INTEGRATED HEADPHONE, SPEAKER AMPLIFIER AND TOUCH SCREEN CONTROLLER

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Table 1. AGC Settings
TSC2101
SLAS392D− JUNE 2003 − REVISED MAY 2005
MIC HEADSET INPUT
MIC HANDSET INPUT
BIT
CONTROL
REGISTER
BIT
CONTROL
REGISTER
AGC enable
D0
01H
D0
1EH
Target gain
D7−D5
01H
D7−D5
1EH
Time constants (attack and decay time)
D4−D1
01H
D4−D1
1EH
Noise threshold
D13−D11
24H
D13−D11
24H
Noise threshold flag
D11
04H
D11
04H
Hysteresis
D10−D9
1DH
D10−D9
1DH
Debounce time (normal to silence mode)
D8−D6
26H
D8−D6
26H
Debounce time (silence to normal mode)
D5−D3
26H
D5−D3
26H
Max PGA applicable
D15−D9
26H
D15−D9
26H
Gain applied by AGC
D15−D8
01H
D15−D8
1EH
Saturation flag
D0
04H
D0
04H
Clip stepping disable
D3
06H
D3
06H
NOTE^: All settings shown in Table 1 are located in Page 2 of control registers.
CELL-PHONE INPUT
BIT
CONTROL
REGISTER
D0
24H
D7−D5
24H
D4−D1
24H
D13−D11
24H
D14
24H
D10−D9
24H
D8−D6
27H
D5−D3
27H
D15−D9
27H
D14−D8
1FH
D7
1FH
D8
24H
Stereo Audio DAC
Each channel of the stereo audio DAC consists of a digital audio processing block, a digital interpolation filter,
digital delta-sigma modulator, and an analog reconstruction filter. The DAC is designed to provide enhanced
performance at low sample rates through increased oversampling and image filtering, thereby keeping
quantization noise generated within the delta-sigma modulator and signal images strongly suppressed within
the audio band to beyond 20 kHz. This is realized by keeping the upsampled rate constant at 128 x Fsref and
changing the oversampling ratio as the input sample rate is changed. For Fsref of 48 kHz, the digital delta−sigma
modulator always operates at a rate of 6.144 MHz. This ensures that quantization noise generated within the
delta-sigma modulator stays within the frequency band below 20 kHz at all sample rates. Similarly, for Fsref
rate of 44.1 kHz, the digital delta-sigma modulator always operates at a rate of 5.6448 MHz.
Digital Audio Processing
The DAC channel consists of optional filters for de-emphasis and bass, treble, midrange level adjustment, or
speaker equalization. The de-emphasis function is only available for sample rates of 32 kHz, 44.1 kHz, and 48
kHz. The transfer function consists of a pole with time constant of 50ms and a zero with time constant of 15ms.
Frequency response plots are given in the Audio Codec Filter Frequency Responses section of this data sheet.
The DAC digital effects processing block consists of a fourth order digital IIR filter with programmable
coefficients (one set per channel). The filter is implemented as cascade of two biquad sections with frequency
response given by:
ǒ Ǔǒ Ǔ ^{N0 ) 2 N1 z*1 ) N2 z*2}
N3 ) 2 N4 z^*1 ) N5 z^*2
32768 * 2 D1 z^*1 * D2 z^*2 32768 * 2 D4 z^*1 * D5 z^*2
The N and D coefficients are fully programmable, and the entire filter can be enabled or bypassed. The
coefficients for this filter implement a variety of sound effects, with bass-boost or treble boost being the most
commonly used in portable audio applications. The default N and D coefficients in the part are given by:
N0 = N3 = 27619
N1 = N4 = −27034
N2 = N5 = 26461
D1 = D4 = 32131
D2 = D5 = −31506
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