Datasheet

TSC2101
SLAS392D JUNE 2003 REVISED MAY 2005
www.ti.com
25
Table 1. AGC Settings
MIC HEADSET INPUT MIC HANDSET INPUT CELL-PHONE INPUT
BIT
CONTROL
REGISTER
BIT
CONTROL
REGISTER
BIT
CONTROL
REGISTER
AGC enable D0 01H D0 1EH D0 24H
Target gain D7D5 01H D7D5 1EH D7D5 24H
Time constants (attack and decay time) D4D1 01H D4D1 1EH D4D1 24H
Noise threshold D13D11 24H D13D11 24H D13D11 24H
Noise threshold flag D11 04H D11 04H D14 24H
Hysteresis D10D9 1DH D10D9 1DH D10D9 24H
Debounce time (normal to silence mode) D8D6 26H D8D6 26H D8D6 27H
Debounce time (silence to normal mode) D5D3 26H D5D3 26H D5D3 27H
Max PGA applicable D15D9 26H D15D9 26H D15D9 27H
Gain applied by AGC D15D8 01H D15D8 1EH D14D8 1FH
Saturation flag D0 04H D0 04H D7 1FH
Clip stepping disable D3 06H D3 06H D8 24H
NOTE
:
All settings shown in Table 1 are located in Page 2 of control registers.
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 deltasigma
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
N0 ) 2 N1 z
*1
) N2 z
*2
32768 * 2 D1 z
*1
* D2 z
*2
Ǔǒ
N3 ) 2 N4 z
*1
) N5 z
*2
32768 * 2 D4 z
*1
* D5 z
*2
Ǔ
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