TEA1098A View Datasheet(PDF) - Philips Electronics

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TEA1098A

Speech and handsfree IC

Philips Electronics 

Philips Semiconductors

Speech and handsfree IC

Product specification

TEA1098A

In the same way, a transmit detector is integrated which, in

standard applications, does not consider input signals

between pins TXI and GNDTX as noise when they have a

level greater than 0.75 mV (RMS). This level is

proportional to RTSEN.

As can be seen from Fig.11, the output of the decision

logic is a current source. The logic table gives the

relationship between the inputs and the value of the

current source. It can charge or discharge the capacitor

CSWT with a current of 10 µA (switch-over). If the current is

zero, the voltage on pin SWT becomes equal to the

voltage on pin IDT via the high-ohmic resistor RIDT (idling).

The resulting voltage difference between pins SWT and

IDT determines the mode of the TEA1098A and can vary

between −400 and +400 mV (see Table 1).

Table 1 Modes of TEA1098A

VSWT − VIDT (mV)

<−180

0

>180

MODE

transmit mode

Idle mode

receive mode

The switch-over timing can be set with CSWT, the Idle

mode timing with CSWT and RIDT. In the basic application

given in Fig.17, CSWT is 220 nF and RIDT is 2.2 MΩ. This

enables a switch-over time from transmit to receive mode

or vice-versa of approximately 13 ms (580 mV swing on

pin SWT). The switch-over time from Idle mode to transmit

mode or receive mode is approximately 4 ms (180 mV

swing on pin SWT).

The switch-over time, from receive mode or transmit mode

to Idle mode is equal to 4 × RIDTCSWT and is approximately

2 seconds (Idle mode time).

The input at pin DLC overrules the decision logic. When

the voltage on pin DLC goes lower than 0.2 V, the

capacitor CSWT is discharged with 10 µA thus resulting in

the transmit mode.

Voice switch (pins STAB and SWR)

A diagram of the voice switch is illustrated in Fig.12. With

the voltage on pin SWT, the TEA1098A voice switch

regulates the gains of the transmit and the receive

channels so that the sum of both is kept constant.

In the transmit mode, the gain of the microphone amplifier

is at its maximum and the gain of the loudspeaker amplifier

is at its minimum. In the receive mode, the opposite

applies. In the Idle mode, both microphone and

loudspeaker amplifier gains are halfway.

The difference between maximum and minimum is the so

called switching range. This range is determined by the

ratio of RSWR and RSTAB and is adjustable between

0 and 52 dB. RSTAB should be 3.65 kΩ and sets an

internally used reference current. In the basic application

diagram given in Fig.17, RSWR is 365 kΩ which results in a

switching range of 40 dB. The switch-over behaviour is

illustrated in Fig.13.

In the receive mode, the gain of the loudspeaker amplifier

can be reduced using the volume control. Since the voice

switch keeps the sum of the gains constant, the gain of the

microphone amplifier is increased at the same time (see

dashed curves in Fig.13). In the transmit mode, however,

the volume control has no influence on the gain of the

microphone amplifier or the gain of the loudspeaker

amplifier. Consequently, the switching range is reduced

when the volume is reduced. At maximum reduction of

volume, the switching range becomes 0 dB.

DUPLEX CONTROLLER

to

microphone

amplifier

from

SWT

Gvtx + Gvrx = C(1)

VOICE SWITCH

25 STAB RSTAB

26 SWR RSWR

from

volume

control

to

loudspeaker

amplifier

(1) C = constant.

FCA154

Fig.12 Voice switch.

2000 Aug 18

16

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