TEA1098 Philips Semiconductors, TEA1098 Datasheet - Page 14

• Manufacturer Part Number: TEA1098
• Description: Speech and handsfree IC
• Manufacturer: Philips Semiconductors

Philips Semiconductors
D
Signal and noise envelope detectors: pins TSEN, TENV,
TNOI, RSEN, RENV and RNOI
The strength of signal level and background noise in both
channels is monitored by signal envelope detectors and
noise envelope detectors respectively. The outputs of the
envelope detectors provide inputs to the decision logic.
The signal and noise envelope detectors are shown in
Fig.10.
For the transmit channel, the signal between pin TXIN and
pin TSEN is amplified by 40 dB. For the receive channel,
the signal between pin HFRX and pin RSEN is amplified
by 0 dB.
The signals between pin TSEN and pin TENV, and
between pin RSEN and pin RENV are logarithmically
compressed and buffered.
The sensitivity of the envelope detectors is set by
resistors R
series with these two resistors block any DC component
and form a first-order high-pass filter.
1999 Oct 14
handbook, full pagewidth
UPLEX CONTROLLER
Speech and handsfree IC
Pin numbers in parenthesis apply to the TEA1098H. Pin numbers not in parenthesis apply to the TEA1098TV.
TSEN
from
microphone
amplifier
DUPLEX CONTROLLER
and R
RSEN
TSEN
8 (4)
LOG
. The capacitors connected in
R TSEN
C TSEN
Fig.10 Signal and noise envelope detectors.
TENV
7 (3)
C TENV
to logic
TNOI
6 (2)
C TNOI
14
from
loudspeaker
amplifier
In the basic application, (see Fig.19), it is assumed that
V
and R
capacitors C
the cut-off frequency is at 160 Hz.
The buffer amplifiers feeding the compressed signals to
pins TENV and RENV have a maximum source current of
120 A and a maximum sink current of 1 A. Capacitors
C
detectors. In the basic application, the value of both
capacitors is 470 nF. Because of the logarithmic
compression, each 6 dB signal increase means an 18 mV
increase on the signal envelopes at pins TENV or RENV
(room temperature). Thus, timings can be expressed in
dB/ms. At room temperature, the 120 A sourced current
corresponds to a maximum signal envelope rise-slope of
85 dB/ms, which is sufficient to track normal speech
signals. The 1 A current sunk by pin TENV or pin RENV
corresponds to a maximum fall-slope of 0.7 dB/ms. This is
sufficient for a smooth envelope and also eliminates the
effect of echoes on switching behaviour.
TXIN
TENV
= 1 mV (RMS) and V
TSEN
and C
RSEN
10 (6)
and R
LOG
TSEN
RENV
R RSEN
C RSEN
RSEN
and C
set the timing of both signal envelope
both have a value of 10 k . When
RSEN
RENV
11 (7)
HFRX
both have a value of 100 nF,
C RENV
= 100 mV (RMS) nominal
to logic
RNOI
Product specification
9 (5)
TEA1098
C RNOI
MGL344