U4091BM-RFNY Atmel, U4091BM-RFNY Datasheet - Page 19

• Manufacturer Part Number: U4091BM-RFNY
• Description: IC PROG PHONE AUDIO PROC 44SSOP
• Manufacturer: Atmel

Specifications of U4091BM-RFNY

• Function: Telephone Audio Processor
• Number Of Circuits: 1
• Voltage - Supply: 3.1 V ~ 3.5 V
• Power (watts): 900mW
• Operating Temperature: -25°C ~ 75°C
• Mounting Type: Surface Mount
• Package / Case: 44-SSOP
• Includes: Speaker Amplifier
• For Use With: DEMOBOARD-U4091BM - BOARD DEMO FOR U4091BM
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant
• Current - Supply: -
• Interface: -

12.1
12.2
12.3
4872B–CORD–01/11
Dial-tone Detector
Background Noise Monitors
4-point Sensing
The dial-tone detector is a comparator with one side connected to the speaker amplifier input
and the other to VM with a 35-mV offset (see
mode, and the incoming signal is greater than 35mV (25mV
change thus disabling the receive idle mode. This circuit prevents the dial tone (which would
be considered as continuous noise) from fading away as the circuit would have the tendency
to switch to idle mode. By disabling the receive idle mode, the dial tone remains at the nor-
mally expected full level.
This circuit distinguishes speech (which consists of bursts) from background noise (a relatively
constant signal level). There are two background-noise monitors, one for the receive path and
the other for the transmit path. The receive background-noise monitor is operated on by the
receive level detector, while the transmit background noise monitor is operated on by the
transmit level detector (see
storing a DC voltage representative of the respective noise levels in capacitors at CBNMR and
CBNMT. The voltages at these pins have slow rise times (determined by the internal current
source and an external capacitor), but fast decay times. If the signal at TLDR (or TLDT)
changes slowly, the voltage at BNMR (or BNMT) will remain more positive than the voltage at
the non-inverting input of the monitor's output comparator. When speech is present, the volt-
age at the non-inverting input of the comparator will rise more quickly than the voltage at the
inverting input (due to the burst characteristic of speech), causing its output to change. This
output is sensed by the mode-control block.
In 4-point-sensing mode, the receive- and the transmit-sensing paths include additional
CLOGs (calculated logarithmic amplifiers). The block MODECON compares the detector out-
put 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 differential output (AFST, AFSR) of the block MODECON controls AFSCON. The effect of
I1-I4 in
• 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
Table 12-1 on page
20.
Figure 12-6 on page
Figure 12-5 on page
22). They monitor the background noise by
Atmel U4091BM-R
rms
), the comparator’s output will
22). If the circuit is in idle
19