Cirrus Logic CDB6422 - Manual (Page 13)

CDB6422
DS295DB2 13
acoustic coupling between AO and APO to -9dB (a
design target).
In a desktop speakerphone, the acoustic coupling is
typically altered by adjusting the mic preamp gain.
In a hands-free car kit, the acoustic coupling is typ-
ically altered by adjusting the speaker and mic po-
sition.
For this exercise, NIN4 should be set to ‘ACTIVE’,
and there should be no signal connected to
NIN_RCA.
1) Configure the CS6422 from RESET with the
following:
reg 0: 57a0 (d7a0 if the internal mic preamp
is used) -- RVol = +9dB
reg 1: 26a2 -- TVol = +12dB
reg 5: 003a -- NSdt = -12dB
2) Adjust the speaker/mic position until the sys-
tem is just on the verge of howling. At this
point the loop gain is approximately equal to
0dB. The above register configuration sets a
gain of +9dB between APO and AO. When the
speaker and mic are placed such that the system
is on the verge of howling, the coupling be-
tween AO and APO is approximately -9dB.
3) In the desktop telephone application (where the
speaker and microphone are not mobile), adjust
the mic preamp gain until the system is just on
the verge of howling.
4.3 Jumper configuration:
Acoustic input using external microphone and in-
ternal mic preamp:
AIN1 = MIC
MIC_BIAS = ENABLED
AIN2 = ACTIVE
AIN3 = FIXED
AIN4 = 0dB
AIN5 = ACTIVE
AIN6 = ON
AIN7 = ON
(Alternate) Acoustic input using AIN_RCA with
no mic bias and internal mic preamp disabled:
AIN1 = RCA
MIC_BIAS = DISABLED
AIN2 = ACTIVE
AIN3 = FIXED
AIN4 = 0dB
AIN5 = ACTIVE
AIN6 = OFF
AIN7 = OFF
-- NOTE: 'Mic' bit in Register 0 should be '0' for
this configuration!
Acoustic output using 3-pole Butterworth filter and
speaker driver set to 0dB (1/4 Watt into 4 ohms).
AOUT1 = ACTIVE
AOUT2 = 3-POLES
AOUT3 = FIXED
AOUT4 = 0dB
AOUT5 = GAINED
AOUT6 = AC
SPEAKER_GAIN = 0dB
Network input (input source varies based on sce-
nario):
NIN1 = ACTIVE
NIN2 = FIXED
NIN3 = 0dB
NIN4 = ACTIVE, POTS(DAA), or CODEC de-
pending on signal source
Network output using 3-pole Butterworth filter:
NOUT1 = ACTIVE
NOUT2 = 3-POLE
NOUT3 = FIXED
NOUT4 = 0dB
NOUT5 = GAINED
NOUT6 = AC
Other Jumper Settings:
HDR94 "RUN" installed
HDR90 "uC" installed
HDR86 "DTMF_TX" installed