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TEA1062AM1 Fiches technique(PDF) 7 Page - NXP Semiconductors |
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TEA1062AM1 Fiches technique(HTML) 7 Page - NXP Semiconductors |
7 / 28 page 1997 Sep 03 7 Philips Semiconductors Product specification Low voltage transmission circuits with dialler interface TEA1062; TEA1062A Sidetone suppression The anti-sidetone network, R1//Zline, R2, R3, R8, R9 and Zbal, (see Fig.4) suppresses the transmitted signal in the earpiece. 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 when |R8//Zbal| << R3. To obtain optimum sidetone suppression, condition (2) has to be fulfilled which results in: Where k is a scale factor; The scale factor k, dependent on the value of R8, is chosen to meet the following criteria: • compatibility with a standard capacitor from the E6 or E12 range for Zbal •Zbal//R8 << R3 fulfilling condition (a) and thus ensuring correct anti-sidetone bridge operation •Zbal + R8 >> R9 to avoid influencing the transmit gain. In practise Zline varies considerably with the line 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. R9 R2 × R1 R3 R8 Z bal × R8 Z bal + ------------------------- + × = Z bal Z bal R8 + ------------------------- Z line Z line R1 + -------------------------- = Z bal R8 R1 -------- Z line kZ line × = × = k R8 R1 -------- = EXAMPLE The balance impedance Zbal at which the optimum suppression is present can be calculated by: Suppose 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; Zbal = 130 Ω + (820 Ω//220 nF). The anti-sidetone 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. The attenuation is almost constant over the whole audio-frequency range. Figure 5 shows a conventional Wheatstone bridge anti-sidetone circuit that can be used as an alternative. Both bridge types can be used with either resistive or complex set impedances. (More information on the balancing of anti-sidetone bridges can be obtained in our publication “Applications Handbook for Wired telecom systems, IC03b”, order number 9397 750 00811.) |
Numéro de pièce similaire - TEA1062AM1 |
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Description similaire - TEA1062AM1 |
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