PCA1070P datasheet(8/36 Pages) PHILIPS

8 / 36 page

1997 Jun 20

Philips Semiconductors

Product speciﬁcation

Multistandard programmable analog

CMOS transmission IC

PCA1070

Fig.5 Microphone arrangements.

handbook, full pagewidth

(a)

(b)

VSS

MIC

−

(c)

VSS

MIC

−

(d)

VSS

MIC

−

MIC

−

MGE341

(a) Dynamic or piezo.

(b) Low impedance electret with built-in pre-amplifier.

(d) Symmetrical connection of electret.

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 k

Ω // 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).

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