CS6403 datasheet(26/54 Pages) CIRRUS

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Automatic Gain Control (AGC)

By default, automatic gain-control is provided in

the far-end receive path (see Figure 3). This

AGC provides dynamic gain changes to keep the

signal strength at the near-end output the same

for weak and strong far-end input signals.

The

AGC may be disabled either via AGCD:

SSI_CR1.10, or by setting the volume control to

level 10.

Real-time controls

The GPIN pins allow real-time control over

common functions such as mute, volume control,

half-duplex control, and echo canceller status.

GPIN3 controls the microphone gain stage status

at reset and mute after reset (see Table 4).

GPIN2, GPIN1, and GPIN0 work in concert to

implement volume control, half-duplex dis-

able/enable, and filter coefficient control.

GPIN3

GPIN3 controls two chip functions: microphone

gain stage and mute.

Immediately after reset,

GPIN3 is sampled and, if high, the 26dB micro-

p h o n e ga in sta g e is disa bled.

With the

microphone gain disabled, full scale input is 1

Vp. With the microphone gain enabled, full scale

is 50 mVp.

1 ms after reset, a change in the state of GPIN3

will mute the transmit path (send all zeroes out

SDO), and set the receive path full on. So, if

GPIN3 was high at reset, setting it low will mute

the microphone.

Restoring the state of GPIN3

will unmute the microphone.

GPIN2/1/0

GPIN2/1/0 act in concert to encode eight states

as described by Table 5 in the pin description

section. These pins are meant to be driven by a

microcontroller or other digital device to allow

user control of the echo canceller.

To enter a

state, the user must apply the appropriate value

at GPIN2/1/0 for 375

µS (3 samples) before the

change will take effect. For example, to increase

the SPKROUT volume by one step, GPIN2/1/0

needs to be: 110.

Applying 110 to GPIN2/1/0

for 375

µS (or longer) will cause the volume to

be raised by 3dB. To again raise the volume by

3dB, the system would have to change state

away from 110 to another state for 375

µS (100

is a don’t care state), then switch back to 110 for

at least 375

µS.

Half-Duplex Disable (011,111)

In some applications, the half-duplex mode of

the CS6403 may be unnecessary or undesirable.

In these cases, the GPIN pins may be used to

d i sab le the half-duplex mode by sett ing

GPIN2/1/0 to either 011 or 111.

Half-Duplex Enable (000)

This state is on by default when the CS6403 is

reset. If the half- duplex mode is disabled using

the 011 or 111 setting, it can be restored by set-

ting GPIN2/1/0 to 000.

Clear Coefficients (001)

Clearing the coefficients of the adaptive filter ef-

fectively disables the echo canceller. This will

force the CS6403 to operate in half- duplex

mode unless half-duplex mode is disabled as de-

scribed above. Clear Coefficients is maintained

only as long as 001 is applied to the GPIN2/1/0

pins.

GPIN3

(at reset)

GPIN3

(1ms after reset)

Action

26 dB enable, no mute

26 dB enable, mute

26 dB disable, mute

26 dB disable, no mute

Table 4. Mute Controls.

CS6403

DS192PP6

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