PCA1070T 查看數據表（PDF） - Philips Electronics
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PCA1070T Datasheet PDF : 36 Pages
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Philips Semiconductors
Multistandard programmable analog
CMOS transmission IC
Product specification
PCA1070
handbook, full pagewidth
MIC+
VP
MIC+
VP
MIC+
VP
MIC+
MIC−
(a)
MIC−
VSS
(b)
MIC−
VSS
(c)
MIC−
VSS
(d) MGE341
(a) Dynamic or piezo.
(b) Low impedance electret with built-in pre-amplifier.
(c) High impedance electret with built-in pre-amplifier.
(d) Symmetrical connection of electret.
Fig.5 Microphone arrangements.
Dynamic limiter
To prevent distortion of the transmitted speech signal, the
gain of the microphone amplifier is reduced rapidly when
signal peaks on the line exceed an internally determined
threshold level. The time in which the gain is reduced, the
attack time, is very short. The circuit stays in this
gain-reduced condition until the peaks of the sending
signal remain below the threshold level. The sending gain
then returns to normal after a time also determined on the
chip, the release time. The threshold level of the AC
peak-to-peak line voltage on pin LN is default at
3.5 V (p-p). A level of 2.6 V (p-p) can be programmed by
setting bit code DLT to logic 1.
The internal threshold level is lowered automatically if the
DC voltage setting of the circuit (VSLPE) is not high enough
to reach the programmed level. Also when the DC current
in the transmit output stage is insufficient to drive the line
load, the internal threshold level is lowered automatically.
Dynamic limiting considerably improves sidetone
performance in over-drive conditions (less distortion and
limited sidetone level).
DTMF channel
The PCA1070 has an asymmetrical DTMF input. Its input
impedance is 200 kΩ // 45 pF and its gain is default at
21 dB. DTMF signals can be sent to the line by setting
control bit ‘Sending Mute’ (SM) to logic 1 (default SM = 0);
by setting ‘Receiving Mute’ (RM) also to logic 1 (default
RM = 0), the dialling tones are also sent to the receiving
output to generate a confidence tone in the earpiece.
The gain between the DTMF input and the line LN can be
programmed between 1 dB and 21 dB in 1 dB steps using
bit code GMAx (6 bits). The confidence tone gain
(between DTMF input and earpiece outputs QR) can be
programmed between −40 dB and −19 dB (symmetrical
drive of earpiece) using bit code GRAx (6 bits). GMAx sets
the gain of the ‘sending prog-amp’ (recommended range in
DTMF mode for Gma = −5 to 15 dB) and GRAx sets the
gain of the ‘rec prog-amp’ (allowed range
Gra = −25 to 0 dB).
1997 Jun 20
8
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