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UTCTEA1062N

LOW VOLTAGE TELEPHONE TRANSMISSION CIRCUIT WITH DIALLER INTERFACE

Unisonic Technologies 

UTC TEA1062N / TEA1062AN

LINEAR INTEGRATED CIRCUIT

cut-off frequency will depend on the time constant

R4*C4. The output voltage of the receiving amplifier is

specified for continuous-wave drive. The maximum

output voltage will be higher under speech conditions

where the peak to RMS ratio is higher.

Automatic gain control input (AGC)

Automatic line loss compensation is achieved by

connecting a resistor(R6) between AGC and VEE. The

automatic gain control varies the gain of the

microphone amplifier and the receiving amplifier in

accordance with the DC line current. The control range

is 5.8dB which corresponds to a line length of 5km for

a 0.5mm diameter twisted pair copper cable with a DC

resistance of 176Ω/km and average attenuation of

1.2dB/km. Resistor R6 should be chosen inaccordance

with the exchange supply voltage and its feeding

bridge resistance(see Fig.12 and Table 1). The ratio of

start and stop currents of the AGC curve is

independent of the value of R6. If no automatic line

loss compensation is required the AGC may be left

open-circuit. The amplifier, in this condition, will give

their maximum specified gain.

Side-tone suppression

The anti-sidetone network, R1//Zline, R2, R3, R8, R9

and Zbal,(see Fig.4) suppresses the transmitted signal

in the earpiece. Compensation is maximum when the

following conditions are fulfilled:

(a) R9*R2=R1[R3+(R8//Zbal)];

(b) [Zbal/(Zbal+R8)]=[Zline/(Zline+R1)];

If fixed values are chosen for R1, R2, R3 and R9 then

condition(a) will always be fullfilled when R8/Zball《R3.

To obtain optimum side-tone suppression condition(b)

has to be fulfilled which results in:

Zbal=(R8/R1) Zline=k*Zline where k is a scale factor;

K=(R8/R1).

The scale factor (k), dependent on the value of R8,

is chosen to meet following criteria:

(a) Compatibility with a standard capacitor from the

E6 or E12 range for Zbal,

(b)｜Zbal//R8｜《R3 fulfilling condition (a) and thus

ensuring correct anti-sidetone bridge operation,

(c) ｜Zbal+R8｜》R9 to avoid influencing the trans-

mitter gain.

In practice Zline varies considerably with the type and

length. The value chosen for Zbal should therefore be

for an average line length thus giving optimum setting

for short or long lines.

Example

The balance impedance Zbal at which the optimum

suppression is present can be calculated by: Suppose

Zline = 210Ω+(1265Ω//140nF) representing a 5km line

of 0.5 mm diameter, copper, twisted pair cable

matched to 600Ω(176Ω/km;38nF/km). When k=0.64

then R8=390Ω,Zbal=130Ω+(820Ω//220nF). At line

currents below 9mA the internal reference voltage is

automatically adjusted to a lower value(typically 1.6V

at 1mA) This means that more sets can be operated in

parallel with DC line voltages (excluding the polarity

guard) down to an absolute minimum voltage of 1.6V.

With line currents below 9mA the circuit has limited

sending and receiving levels. The internal reference

voltage can be adjusted by means of an external

resistor(RVA). This resistor when connected between

LN and REG will decrease the internal reference

voltage and when connected between REG and SLPE

will increase the internal reference voltage. Current(Ip)

available from VCC for peripheral circuits depends on

the external components used. Fig.9 shows this

current for VCC > 2.2V. If MUTE is LOW (1062 is HIGH)

when the receiving amplifier is driven the available

current is further reduced. Current availability can be

increased by connecting the supply IC(1081) in

parallel with R1, as shown in Fig.16(c), or, by

increasing the DC line voltage by means of an

external resistor(RVA) connected between REG and

SLPE.

UTC

UNISONIC TECHNOLOGIES CO., LTD. 7

QW-R108-011,A

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