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TEA1113

Low voltage versatile telephone transmission circuit with dialler interface

Philips Electronics 

Philips Semiconductors

Low voltage versatile telephone

transmission circuit with dialler interface

Product specification

TEA1113

The internal circuitry of the TEA1113 is supplied from

pin VCC. This voltage supply is derived from the line

voltage by means of a resistor (RCC) and must be

decoupled by a capacitor CVCC. It may also be used to

supply peripheral circuits such as dialling or control

circuits. The VCC voltage depends on the current

consumed by the IC and the peripheral circuits as shown

by the formula (see also Figs 5 and 6). RCCint is the internal

impedance of the voltage supply point, and Irec is the

current consumed by the output stage of the earpiece

amplifier.

VCC = VCCO – RCCint × (Ip – Irec)

VCCO = VLN – RCC × ICC

The DC line current flowing into the set is determined by

the exchange supply voltage (Vexch), the feeding bridge

resistance (Rexch), the DC resistance of the telephone line

(Rline) and the reference voltage (Vref). With line currents

below 8 mA, the internal reference voltage (generating

Vref) is automatically adjusted to a lower value. This means

that more sets can operate in parallel with DC line voltages

(excluding the polarity guard) down to an absolute

minimum voltage of 1.6 V. At currents below 8 mA, the

circuit has limited sending and receiving levels. This is

called the low voltage area.

handbook, halfpage

RCCint VCC

VCCO

Irec

VEE

PERIPHERAL

CIRCUIT

IP

MBE792

Fig.5 VCC voltage supply for peripherals.

Set impedance

In the audio frequency range, the dynamic impedance is

mainly determined by the RCC resistor. The equivalent

impedance of the circuits is illustrated in Fig.7.

LED supply (pin ILED)

The TEA1113 gives an on-hook/off-hook status indication.

This is achieved by a current made available to drive an

LED connected between pins ILED and LN. In the low

voltage area, which corresponds to low line current

conditions, no current is available for this LED. For line

currents higher than a threshold current, the ILED current

increases proportionally to the line current (with a ratio of

one third).The ILED current is internally limited to 19.5 mA

(see Fig.8).

For 17 mA < Iline < 77 mA:

ILED = I--l--i-n---e--3--–----1----7--

This LED driver is referenced to SLPE. Consequently, all

the ILED supply current will flow through the RSLPE resistor.

The AGC characteristics are not disturbed (see Fig.3 for

the supply configuration).

Microphone amplifier (pins MIC+, MIC− and GAS)

The TEA1113 has symmetrical microphone inputs.

The input impedance between pins MIC+ and MIC− is

64 kΩ (2 × 32 kΩ). The voltage gain from pins MIC+/MIC−

to pin LN is set to 51.8 dB (typ). The gain can be

decreased by connecting an external resistor RGAS

between pins GAS and REG. The adjustment range is

13 dB. A capacitor CGAS connected between pins GAS

and REG can be used to provide a first-order low-pass

filter. The cut-off frequency corresponds to the time

constant CGAS × (RGASint // RGAS). RGASint is the internal

resistor which sets the gain with a typical value of 69 kΩ.

Automatic gain control is provided on this amplifier for line

loss compensation.

Dynamic limiter and microphone mute

(pin DLS/MMUTE)

The dynamic limiter only acts on the microphone channel,

this is to prevent clipping of the line signal. To prevent

distortion, the microphone gain is rapidly reduced when

peaks on the line signal exceed an internally determined

threshold level or when the current in the transmit output

stage is insufficient. The time in which the gain reduction

is realized is very short (attack time). The microphone

channel stays in the reduced gain condition until the peaks

1997 Mar 27

6

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