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參數(shù)資料
| 型號(hào)： | TEA1085 |
| 廠商： | NXP SEMICONDUCTORS |
| 元件分類： | 通信及網(wǎng)絡(luò) |
| 英文描述： | Listening-in circuit for line-powered telephone sets |
| 中文描述： | SPECIALTY TELECOM CIRCUIT, PDIP24 |
| 封裝： | 0.600 INCH, PLASTIC, DIP-24 |
| 文件頁數(shù)： | 12/32頁 |
| 文件大?。?/td> | 199K |
| 代理商： | TEA1085 |
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March 1992
12
Philips Semiconductors
Preliminary specification
Listening-in circuit for line-powered
telephone sets
TEA1085; TEA1085A
This reaction time is the 'attack delay time' and ensures
minimum sensitivity of the system for own speech.
The first threshold level at DTI is determined by the
equation:
I
2
Where: I
DCA
= the DC current into DCA
With the component values given in Fig.16, I
DCA
= 11
μ
A
thus V
DTI1
= 18.8 mV.
Listen-in mode
During normal speech the discharge of the capacitor
connected to LLC is not sufficient to reach the threshold
level whereby the system switches to the Larsen mode.
This is because normal speech is not continuous, the
discharge of C26 is slow (attack delay) and the charge is
fast.
The slope of V
LLC
during charge is given in the equation:
V
τ
With C26 = 1
μ
F and R36 = 120 k
this results in
S
1i
= 10 V/s.
Discharge of the capacitor at LLC occurs when the signal
at DTI exceeds V
DTI1
, thus for a continuous signal at DTI
the attack delay time t
ad
(see Fig.10) is determined by the
equation:
×
2
3
k
1
–
×
(
)
×
Where k = t
1
/ T
The duty cycle is determined by the time in which the first
threshold level (V
DTI1
) is exceeded by the signal level at
DTI (see Fig.11) thus for large signals; k
≤
0.5.
With the component values given in Fig.16; k
≥
0.457 for
signals
≥
100 mV(RMS).
Consequently 120 ms
≤
t
ad
≤
160 ms, for
V
DTI
≥
100 mV(RMS)
V
DTI1
R25
-----------
-----------
–
2
R33
×
×
if f > f3 in Fig.9
(
)
=
S
1i
----------------
=
----------------------------
V s
(
)
=
t
ad
-------------------------------------
=
Larsen mode
After the 'attack delay time' the circuit switches from the
listen-in mode to the Larsen mode. The gain of the
loudspeaker amplifier is reduced quickly to a value
(t
LAa
= Larsen attack time, see Fig.10) whereby the
residual Larsen signal is determined by a second
threshold level. This level can be set by resistor R34
connected between THL2 and V
SS
. The second threshold
level must always be selected at a lower level than the first
threshold level thus R34
>
R35.
The time taken to effect gain reduction is very short. In the
Larsen mode the circuit acts as a dynamic limiter with peak
detector and regulates the gain so that the signal level at
DTI is determined by the second threshold level V
DTI2
.
The second threshold level at DTI is determined by the
equation:
I
2
Where: I
DCA
= the DC current into DCA
With the component values given in Fig.16,
V
DTI2
= 6.9 mV.
The charge current in the Larsen mode is reduced to half
the charge current in the listen-in mode.
The slope of V
LLC
during charge (see Fig.10) is given in the
equation:
V
τ
Where: C26 = 1
μ
F and R36 = 100 k
, S
la
= 5 V/s
When the Larsen effect stops (total open-loop gain
<
1) the
gain of the loudspeaker amplifier will return to its normal
value in a time period known as the 'Larsen release time'
(t
LAr
). This time period is determined by capacitor C26
connected to LLC and resistor R36 connected to SIC.
Where: C26 = 1
μ
F and R36 = 120 k
, t
LAr
= 250 ms
In practice the choice of the threshold levels (determined
by R35 and R34) depends on the sensitivity of the
microphone and loudspeaker, the send and receive gains,
sidetone suppression and the acoustical properties which
are determined by the cabinet of the telephone set.
V
DTI2
R34
-----------
-----------
–
2
R33
if f > f3 in Fig.9
(
)
×
×
=
S
la
----------------
C26
2
×
R34
×
--------------------------------------
V s
(
)
=
=
相關(guān)PDF資料 |
PDF描述 |
|---|---|
| TEA1085A | Listening-in circuit for line-powered telephone sets |
| TEA1085AT | Listening-in circuit for line-powered telephone sets |
| TEA1085T | Listening-in circuit for line-powered telephone sets |
| TEA1093 | Hands-free IC |
| TEA1093T | Hands-free IC |
相關(guān)代理商/技術(shù)參數(shù) |
參數(shù)描述 |
|---|---|
| TEA1085A | 制造商:PHILIPS 制造商全稱:NXP Semiconductors 功能描述:Listening-in circuit for line-powered telephone sets |
| TEA1085AT | 制造商:PHILIPS 制造商全稱:NXP Semiconductors 功能描述:Listening-in circuit for line-powered telephone sets |
| TEA1085T | 制造商:PHILIPS 制造商全稱:NXP Semiconductors 功能描述:Listening-in circuit for line-powered telephone sets |
| TEA1088T | 制造商:未知廠家 制造商全稱:未知廠家 功能描述:SMPS Battery Charger Control Circuit |
| TEA1093 | 制造商:PHILIPS 制造商全稱:NXP Semiconductors 功能描述:Hands-free IC |
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