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PDF TEA1085T Data sheet ( Hoja de datos )
| Número de pieza | TEA1085T | |
| Descripción | Listening-in circuit for line-powered telephone sets | |
| Fabricantes | NXP Semiconductors | |
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INTEGRATED CIRCUITS
DATA SHEET
TEA1085; TEA1085A
Listening-in circuit for line-powered
telephone sets
Preliminary specification
File under Integrated Circuits, IC03A
March 1992
1 page  
Philips Semiconductors
Listening-in circuit for line-powered
telephone sets
PIN CONFIGURATION
SYMBOL PIN
DESCRIPTION
VSS
SUP
1 negative supply
2 positive supply
SDC
3 supply amplifier decoupling
SREF
4 supply reference input
LSI1
5 loudspeaker amplifier input 1
LSI2
6 loudspeaker amplifier input 2
GSC2
7 logic input 2 for gain select
GSC1
8 logic input 1 for gain select
LAI−
9 Larsen limiter preamplifier inverting
input
LAI+
10 Larsen limiter preamplifier
non-inverting input
QLA
11 Larsen limiter preamplifier output
LLC 12 Larsen limiter capacitor
THL2
13 Larsen limiter residual threshold level
THL1
14 Larsen limiter attack delay threshold
level
DTI 15 Larsen limiter detector input
DCA
16 Larsen limiter detector current
adjustment
SIC 17 Larsen limiter current stabilizer
VA 18 VBB voltage adjustment
PD 19 power-down input
MUTE
20 MUTE input
QLS1
21 loudspeaker amplifier output 1
QLS2
22 loudspeaker amplifier output 2
DLC
23 dynamic limiter capacitor
VBB 24 stabilized supply decoupling
Preliminary specification
TEA1085; TEA1085A
handbook, halfpage
VSS 1
SUP 2
24 VBB
23 DLC
SDC 3
22 QLS2
SREF 4
21 QLS1
LSI1 5
20 MUTE
LSI2 6 TEA1085 19 PD
GSC2 7 TEA1085A 18 VA
GSC1 8
17 SIC
LAI− 9
16 DCA
LAI+ 10
15 DTI
QLA 11
14 THL1
LLC 12
13 THL2
MLA415
Fig.2 Pin configuration.
March 1992
5
5 Page 
Philips Semiconductors
Listening-in circuit for line-powered
telephone sets
Preliminary specification
TEA1085; TEA1085A
Larsen limiter detector (DTI and DCA) pins 15 and 16
The QLA output signal is AC coupled to the detector input
DTI. DTI is biased by potential divider R30 and R31. The
voltage applied to DTI of the Larsen level limiter is
converted into a current for further processing in this
circuit. Current adjustment is achieved using the network
connected between DCA and VBB (see Fig.8).
The equation for DC current is:
IDCA = R-----3----0R-----+3----0R-----3----1- × VBB × R-----3----2-----+1----R-----3----3-
The equation for AC current is:
iDCA = -VR----D-3--T-3--I for f > 12-- π R33 C25
In the basic application:
R30 = 100 kΩ, R31 = 220 kΩ, R33 = 500 Ω, R32 = 100 kΩ
and C25 = 330 nF
This results in IDCA = 11 µA and the equation:
-i-D----C---A-- = 2 (mA/V)
VDTI
High-pass filter
A third order high-pass filter is created between the
microphone input voltage and the current flowing into
DCA. The cut-off frequencies (see Fig.9) of the three
sections are:
f1 = -2---π----R-----e-1--g--C-----2----4- where Req = R-R----33----00-----+×----RR-----33----11-
f2 = 2----π----R-----3-1--3----C-----2---4--
f3 = 2----π----R-----2-1--6----C-----2---3-- = 1/(2πR25C22 )
Where: R25 = R26 and C22 = C23
The filter reduces the sensitivity of the system to own
speech.
Normal speech is in the frequency range 300 Hz to
3400 Hz, however, the Larsen signal normally occurs at a
frequency > 3 kHz.
With the component values as used in the basic
application (see Fig.16); f1 = 500 Hz, f2 = 1 kHz and
f3 = 3 kHz
handbook, halfgpage
20 log go
(dB)
0
f1 f2 f3
20 log f
6 dB per octave
12 dB per octave
18 dB per octave
speech
Larsen
MGR038
Fig.9 Third-order high-pass filter.
Where:
g
=
i--D----C---A--
Vm
go = R-A----p3---r-3e-
Larsen limiter capacitor (LLC) pin 12
A 1 µF capacitor (C26) is connected externally between
VSS and LLC to determine the attack and release timing of
the Larsen level limiter in the listen-in and Larsen mode.
The timing is also dependent on the value of the resistor
connected between SIC and VSS.
Larsen level limiter threshold (THL1 and THL2) pins
13 and 14
When the signal at DTI exceeds the first threshold level the
capacitor connected to LLC will start to discharge. The first
threshold level is determined by the value of the resistor,
R35, connected to THL1 and VSS. The amount of
discharge of C26 depends on how much the level of the
signal at DTI exceeds the first threshold level (for normal
speech the discharge is small).
The Larsen effect is generally defined as a signal level of
≥ 100 mV(RMS), on line, for a period of more than 100 ms.
The Larsen signal must be reduced to a low level within
200 ms. For Larsen signal levels (f > f3 in Fig.9) of
≥ 100 mV(RMS) at DTI and, with the component values of
Fig.16, the system will switch from the listen-in mode to the
Larsen mode in a time period of 100 ms to 200 ms;
consequently, the initial Larsen effect will last only for a
short period of time.
March 1992
11
11 Page | ||
| Páginas | Total 30 Páginas | |
| PDF Descargar | [ Datasheet TEA1085T.PDF ] | |
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