TEA1062NG-S16-R datasheet(8/13 Pages) UTC

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TEA1062N/TEA1062AN

LINEAR INTEGRATED CIRCUIT

UNISONICTECHNOLOGIESCO.,LTD

8 of 13

www.unisonic.com.tw

QW-R108-011.C

FUNCTIONAL DESCRIPTION(Cont.)

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=100k

Ω). 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 subtracting 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 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 176

Ω/km and average attenuation of 1.2dB/km. Resistor R6 should be chosen

in accordance 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:

If fixed values are chosen for R1, R2, R3 and R9 then condition(a) will always be fulfilled when ︱R8//ZBAL︱<<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,

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 ZILINE =

210

Ω+(1265Ω//140nF) representing a 5km line of 0.5 mm diameter, copper, twisted pair cable matched to

600

Ω(176Ω/km;38nF/km). When k=0.64 then R8=390Ω, ZBAL=130Ω+(820Ω//220nF).

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