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TEA1066T

Versatile telephone transmission circuit with dialler interface

Philips Electronics 

Philips Semiconductors

Versatile telephone transmission circuit

with dialler interface

Product specification

TEA1066T

The voltage regulator adjusts the average voltage on

LN to:

VLN = Vref + ISLPE × R9

or

VLN = Vref + (Iline − ICC − 0.5 × 10−3A − Ip) × R9

where Vref is an internally generated temperature

compensated reference voltage of 4.2 V and R9 is an

external resistor connected between SLPE and VEE.

The preferred value for R9 is 20 Ω. Changing the value of

R9 will also affect microphone gain, DTMF gain, gain

control characteristics, side-tone level and the maximum

output swing on LN.

Under normal conditions, when ISLPE >> ICC + 0.5 mA + Ip,

the static behaviour of the circuit is that of a 4.2 V regulator

diode with an internal resistance equal to that of R9. In the

audio frequency range, the dynamic impedance is largely

determined by R1 (see Fig.3).

LN

handbook, halfpage

L eq

Rp

V ref

REG

R1

VCC

and > 3 V, this being the minimum supply voltage for most

CMOS circuits, including voltage drop for an enable diode.

If MUTE is LOW, the available current is further reduced

when the receiving amplifier is driven.

Microphone inputs MICL+, MICH+, MICL− and MICH−

and amplification adjustment connections GAS1 and

GAS2

The TEA1066T has symmetrical microphone inputs.

The MICL+ and MICL− inputs are intended for

low-sensitivity, low-impedance dynamic or magnetic

microphones. The input impedance is 8.2 kΩ (2 × 4.1 kΩ)

and its voltage gain is typically 52 dB. The MICH+ and

MICH− inputs are intended for a piezoelectric microphone

or an electret microphone with a built-in FET source

follower. Its input impedance is 40.8 kΩ (2 × 20.4 kΩ) and

its voltage gain is typical 38 dB.

The arrangements with the microphone types mentioned

are shown in Fig.9.

The gain of the microphone amplifier in both types can be

adjusted over a range of ±8 dB to suit the sensitivity of the

transducer used. The gain is proportional to external

resistor R7 connected between GAS1 and GAS2.

An external capacitor C6 of 100 pF between GAS1 and

SLPE is required to ensure stability. A larger value may be

chosen to obtain a first-order low-pass filter. The cut-off

frequency corresponds with the time constant R7 × C6.

V EE

R9

20 Ω

C3

4.7 µF

C1

100 µF

MBA454

Rp = 17.5 kΩ

Leq = C3 × R9 × Rp

Fig.3 Equivalent impedance circuit.

The internal reference voltage can be adjusted by means

of an external resistor RVA. This resistor, connected

between LN and REG (pins 1 and 18), will decrease the

internal reference voltage; when connected between REG

and SLPE (pins 18 and 20) it will increase the internal

reference voltage.

Current Ip, available from VCC for supplying peripheral

circuits, depends on external components and on the line

current. Figure 8 shows this current for VCC > 2.2 V

Mute input MUTE

A HIGH level at MUTE enables the DTMF input and

inhibits the microphone inputs and the receiving amplifier;

a LOW level or an open circuit has the reverse effect.

Switching the mute input will cause negligible clicks at the

earpiece outputs and on the line.

Dual-tone multi frequency input DTMF

When the DTMF input is enabled, dialling tones may be

sent onto the line. The voltage gain from DTMF to LN is

typically 25.5 dB and varies with R7 in the same way as

the gain of the microphone amplifier. The signalling tones

can be heard in the earpiece at a low level (confidence

tone).

Receiving amplifier: IR, QR+, QR− and GAR

The receiving amplifier has one input IR and two

complementary outputs, a non-inverting output QR+ and

an inverting output QR−.

1996 Apr 04

5

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