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TEA1066T Datasheet(PDF) 6 Page - NXP Semiconductors |
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TEA1066T Datasheet(HTML) 6 Page - NXP Semiconductors |
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6 / 24 page  1996 Apr 04 6 Philips Semiconductors Product specification Versatile telephone transmission circuit with dialler interface TEA1066T These outputs may be used for single-ended or for differential drive, depending on the sensitivity and type of earpiece used (see Fig.10). Gain from IR to QR+ is typically 25 dB. This will be sufficient for low-impedance magnetic or dynamic earpieces, which are suited for single-ended drive. By using both outputs (differential drive), the gain is increased by 6 dB and differential drive becomes possible. This feature can be used when the earpiece impedance exceeds 450 Ω (high-impedance dynamic, magnetic or piezoelectric earpieces). 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 ratio of peak to RMS value is higher. The receiving amplifier gain can be adjusted over a range of ±8 dB to suit the sensitivity of the transducer used. The gain is set by the external resistor R4 connected between GAR and QR+. Two external capacitors, C4 = 100 pF and C7 = 10 × C4 = 1 nF, are necessary to ensure stability. A larger value of C4 may be chosen to obtain a first-order, low-pass filter. The ‘cut-off’ frequency corresponds with the time constant R4 × C4. Automatic gain control input AGC Automatic line loss compensation is obtained by connecting a resistor R6 between AGC and VEE. This automatic gain control varies the microphone amplifier gain and the receiving amplifier gain in accordance with the DC line current. The control range is 6 dB. This corresponds with a line length of 5 km for a 0.5 mm diameter copper twisted-pair cable with a DC resistance of 176 Ω/km and an average attenuation of 1.2 dB/km. Resistor R6 should be chosen in accordance with the exchange supply voltage and its feeding bridge resistance (see Fig.11 and Table 1). Different values of R6 give the same ratio of line currents for start and end of the control range. If automatic line loss compensation is not required, AGC may be left open. The amplifiers then all give their maximum gain as specified. Power-down input PD During pulse dialling or register recall (timed loop break) the telephone line is interrupted, as a consequence it provides no supply for the transmission circuit and the peripherals connected to VCC. These gaps have to be bridged by the charge in the smoothing capacitor C1. The requirements on this capacitor are relaxed by applying a HIGH level to the PD input during the time of the loop break, which reduces the supply current from typically 1 mA to typically 55 µA. A HIGH level at PD further disconnects the capacitor at REG, with the effect that the voltage stabilizer will have no switch-on delay after line interruptions. This results in no contribution of the IC to the current waveform during pulse dialling or register recall. When this facility is not required PD may be left open. Side-tone suppression Suppression of the transmitted signal in the earpiece is obtained by the anti-side-tone network consisting of R1//Zline, R2, R3, R8, R9 and Zbal (see Fig.14). Maximum compensation is obtained when the following conditions are fulfilled: (1) (2) If fixed values are chosen for R1, R2, R3, and R9, then condition (1) will always be fulfilled, provided that R8//Zbal < R3. To obtain optimum side-tone suppression, condition (2) has to be fulfilled, resulting in: Zbal = (R8/R1) Zline = k × Zline, where k is a scale factor: k = (R8/R1). Scale factor k (dependent on the value of R8) must be chosen to meet the following criteria: 1. Compatibility with a standard capacitor from the E6 or E12 range for Zbal 2. Z bal//R8 << R3 3. Zbal + R8 >> R9. In practice, Zline varies greatly with line length and cable type; consequently, an average value has to be chosen for Zbal. The suppression further depends on the accuracy with which Zbal/k equals the average line impedance. Example: The balanced line impedance Z bal at which the optimum suppression is preset can be calculated by: Assume Zline = 210 Ω + (1265 Ω/140 nF), representing a 5 km line of 0.5 mm diameter, copper, twisted-pair cable matched to 600 Ω (176 Ω/km; 38 nF/km). When k = 0.64, then R8 = 390 Ω; Z bal = 130 Ω + (820 Ω//220 nF). The anti-side-tone network for the TEA1060 family shown in Fig.4 attenuates the signal received from the line by 32 dB before it enters the receiving amplifier. R9 R2 × R1 R3 R8//Z bal [ ] + ( ) = Z bal Z bal R8 + ( ) ⁄ Z line Z line R1 + ( ) ⁄ = |
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