TSC2117 datasheet(30/192 Pages) TI

30 / 192 page

TSC2117

Low-Power Audio Codec With Embedded miniDSP, Stereo Class-D

Speaker Amplifier, and Smart Four-Wire Touch-Screen Controller

SLAS550A – APRIL 2009 – REVISED JUNE 2009

www.ti.com

Noise threshold is a reference level. If the input speech average value falls below the noise threshold,

the AGC considers it as a silence and hence brings down the gain to 0 dB in steps of 0.5 dB every sample

period and sets the noise-threshold flag. The gain stays at 0 dB unless the input speech signal average

rises above the noise-threshold setting. This ensures that noise is not amplified in the absence of speech.

The noise-threshold level in the AGC algorithm is programmable from –30 dB to –90 dB for the

microphone input. When the AGC noise threshold is set to –70 dB, –80 db, or –90 dB, the microphone

input maximum PGA applicable setting must be greater than or equal to 11.5 dB, 21.5 dB, or 31.5 dB,

respectively. This operation includes debounce and hysteresis to prevent the AGC gain from cycling

between high gain and 0 dB when signals are near the noise threshold level. When the noise-threshold

flag is set, the status of the gain applied by the AGC and the saturation flag should be ignored.

Programming the noise debounce is done by writing to page 0/register 91, bits D4–D0. Programming the

signal debounce is done by writing to page 0/register 92, bits D3–D0.

Max PGA applicable allows the user to restrict maximum gain applied by AGC. This can be used for

limiting PGA gain in situations where environmental noise is greater than the programmed noise threshold.

Microphone input maximum PGA can be programmed from 0 dB to 59.5 dB in steps of 0.5 dB.

Programming the maximum PGA gain allowed by the AGC is done by writing to page 0/register 88,

bits D6–D0.

See Table 5-15 for various AGC programming options. AGC can be used only if the microphone input is

routed to the ADC channel.

Table 5-15. AGC Settings(1)

CONTROL REGISTER

BIT

FUNCTION

D5 (Read-only)

AGC saturation flag

D3 (Read-only)

ADC saturation flag

D6 (Read-only)

Signal to level setting of noise threshold

AGC enable

D6–D4

Target level

D7–D6

Hysteresis

D5–D1

Noise threshold

D6–D0

Maximum PGA applicable

D7–D0

Time constants (attack time)

D7–D0

Time constants (decay time)

D4–D0

Debounce time (noise)

D3–D0

Debounce time (signal)

D7–D0 (Read-only)

Gain applied by AGC

(1)

All registers shown in this table are located on page 0.

APPLICATION INFORMATION

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