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UTCTEA1062N

LOW VOLTAGE TELEPHONE TRANSMISSION CIRCUIT WITH DIALLER INTERFACE

Unisonic Technologies 

UTC TEA1062N / TEA1062AN

LINEAR INTEGRATED CIRCUIT

FUNCTIONAL DESCRIPTION

Supply: VCC, LN, SLPE, REG and STAB

Power for the UTC TEA1062N/TEA1062AN and its

peripheral circuits is usually obtained from the

telephone line. The IC supply voltage is derived from

the line via a dropping resistor and regulated by the

UTC TEA1062N/TEA1062AN,The supply voltage Vcc

may also be used to supply external circuits e.g.

dialling and control circuits. Decoupling of the supply

voltage is performed by a capacitor between Vcc and

VEE while the internal voltage regulator is decoupled

by a capacitor between REG and VEE. The DC current

drawn by the device will vary in accordance with

varying values of the exchange voltage(Vexch), the

feeding bridge resistance(Rexch) and the DC resistance

of

the telephone line(Rline). The UTC

TEA1062N/TEA1062AN has an internal current

stabilizer operating at a level determined by a 3.6kΩ

resistor connected between STAB and VEE( see

Fig.8). When the line current(Iline) is more than 0.5 mA

greater than the sum of the IC supply current ( Icc) and

the current drawn by the peripheral circuitry connected

to VCC(lp) the excess current is shunted to VEE via LN.

The regulated voltage on the line terminal(VLN) can be

calculated as:

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 3.7V and R9 is an

external resistor connected between SLPE and VEE. In

normal use the value of R9 would be 20Ω. Changing

the value of R9 will also affect microphone gain, DTMF

gain,gain control characteristics, side tone level,

maxmimum output swing on LN and the DC

characteristics (especially at the lower voltages). Under

normal conditions, when ISLPE>=ICC+0.5mA +Ip, the

static behaviour of the circuit is that of a 3.7V regulator

diode with an internal resistance equal to that of

R9.In the audio frequency range the dynamic

impedance is largely determined by R1.Fig.3 shows

the equivalent impedance of the circuit.

Microphone inputs(MIC+ and MIC-) and

gain pins (GAS1 and GAS2)

The UTC TEA1062N/TEA1062AN has symmetrical

inputs. Its input impedance is 64kΩ (2*32kΩ) and its

voltage gain is typically 52 dB (when R7=68kΩ.see

Fig.13). Dynamic, magnetic, piezoelectric or electret

(with built-in FET source followers) can be used.

Microphone arrangements are illustrated in Fig.10. The

gain of the microphone amplifier can be adjusted

between 44dB and 52dB to suit the sensitivity of the

transducer in use. The gain is proportional to the value

of R7 which is connected between GAS1 and GAS2.

Stability is ensured by the external capacitors, C6

connected between GAS1 and SLPE and C8

connected between GAS1 and VEE. The value of C6

is 100pF but this may be increased to obtain a

first-order low-pass filter. The value of C8 is 10 times

the value of C6. The cut-off frequency corresponds to

the time constant R7*C6.

Mute input (MUTE)

A LOW(UTC TEA1062N is HIGH) level at MUTE

enables DTMF input and inhibites the microphone

inputs and the receiving amplifier inputs; a HIGH(UTC

TEA1062N is LOW) level or an open circuit does the

reverse. Switching the mute input will cause negligible

clickis at the telephone outputs and on the line. In case

the line current drops below 6mA(parallal opration of

more sets) the circuit is always in speech condition

independant of the DC level applied to the MUTE input.

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 25.5dB(when R7=68kΩ) and varies with

R7 in the same way as the microphone gain. The

signalling tones can be heard in the earpiece at a low

level(confidence tone).

Receiving amplifier (IR,QR and GAR)

The receiving amplifier has one input (IR) and a

non-inverting output (QR). Earpiece arrangements are

illustrated in Fig.11. The IR to QR gain is typically 31dB

(when R4=100kΩ). It can be adjusted between 20 and

31dB to match the sensitivity of the transducer in use.

The gain is set with the value of R4 which is connected

between GAR and QR.The overall receive gain,

between LN and QR, is calculated by substracting the

anti-sidetone network attenuation (32dB) from the

amplifier gain. Two external capacitors, C4 and C7,

ensure stability. C4 is normally 100pF and C7 is 10

times the value of C4. The value of C4 may be

increased to obtain a first-order low-pass filter.The

UTC UNISONIC TECHNOLOGIES CO., LTD. 6

QW-R108-011,A

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