TEA1094AT View Datasheet(PDF) - Philips Electronics

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TEA1094AT

Hands free IC

Philips Electronics 

Philips Semiconductors

Hands free IC

Product specification

TEA1094; TEA1094A

As can be seen from Fig.9, 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 SWT becomes equal to the voltage on IDT via

the high-ohmic resistor RIDT (idling). The resulting voltage

difference between SWT and IDT determines the mode of

the TEA1094 (TEA1094A) and can vary between

−400 and +400 mV (see Table 1).

Table 1 Modes of TEA1094; TEA1094A

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.13, 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

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

mode or receive mode is approximately 4 ms (180 mV

swing on 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 inputs MUTET and DLC/MUTER overrule the decision

logic. When MUTET goes HIGH, the capacitor CSWT is

charged with 10 µA thus resulting in the receive mode.

When the voltage on pin DLC/MUTER 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.10. With

the voltage on SWT, the TEA1094 (TEA1094A)

voice-switch regulates the gains of the transmit and the

receive channel 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.13, RSWR is 365 kΩ which results in a

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

illustrated in Fig.11.

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.11). 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

STAB

13

(10)

RSTAB

SWR

RSWR

12

(9)

from

volume

control

to

loudspeaker

amplifier

MGD225

The pin numbers given in parenthesis refer to the TEA1094A.

(1) C = constant.

Fig.10 Voice switch.

1996 Jul 15

12

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