U4091BM-N Datasheet, PDF (19/38 Pages) ATMEL Corporation – PROGRAMMABLE TELEPHONE AUDIO PROCESSOR

4-point Sensing
U4091BM-N
In 4-point sensing mode, the receive- and the transmit-sensing path include additional
CLOGs (Calculated Logarithmical amplifiers). The block MODECON compares the
detector output signals and decides whether receive-, transmit- or idle mode has to be
activated. Depending on the mode decision, MODECON generates a differential voltage
to control AFSCON.
The MODECON block has seven inputs:
• The output of the transmit log (LOGT) the comparison of LOGT, CLOGR
• The output of the receive clog (CLOGR) - designated I1
• The output of the transmit clog (CLOGT) the comparison of CLOGT, LOGR
• The output of the receive log (LOGR) - designated I2
• The output of the transmit background-noise monitor (BNMT) - designated I3
• The output of the receive background-noise monitor (BNMR) - designated I4
• The output of the dial-tone detector
The differential output (AFST, AFSR) of the block MODECON controls AFSCON. The
effect of I1-I4 in Table 9.
Table 9. Mode Decision for Signal Sensing
Input
I1
I2
I3
I4
T
T
S
X
T
R
Y
Y
R
T
Y
Y
R
R
X
S
T
T
N
X
T
R
N
N
R
T
N
N
R
R
X
N
Note: X = do not care; Y = I3 and I4 are not both noise.
Output
Mode
Transmit
Change mode
Change mode
Receive
Idle
Idle
Idle
Idle
LOGT > CLOGR
LOGT < CLOGR
LOGR < CLOGT
LOGR > CLOGT
BNMT detects speech
BNMT detects noise
BNMR detects speech
BNMR detects noise
I1 = T
I1 = R
I2 = T
I2 = R
I3 = S
I3 = N
I4 = S
I4 = N
19
4666B–CORD–08/04