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126 Fig. 15 Transmission diagram Fig. 16 (right) Transmission diagram with automatic level regulation. Sending and receiving The microphone signal is amplified in the microphone amplifier (AM) and is fed out to the line at points B and E, which also constitute feeding points for the direct current to the microphone amplifier. The speech circuit introduced in ERI- COFON 700 has no transmission regulation. However, as the feeding loss of the microphone is eliminated (constant amplification of direct currents from 100 mA down to < 10 mA), the transmission characteristics of the non-regulated circuit are better than those of the traditional carbon set. Further improvement of the transmission characteristics of the set can be obtained by introducing regulation of the sending and receiving level, which compensates the speech frequency attenuation caused by the subscriber line in accordance with the following principle. A constant sending or receiving level irrespective of the attenuation of the subscriber line is obtained by introducing attenuation networks, Z3 and Z4 respectively in fig. 16. The value of the impedance Z3 or Z4 is a function of the direct current on the line. When the line current is high, i.e. a short line, the impedance is low and the level to the microphone or receiver amplifier is attenuated. When the length of the line increases and the direct current decreases, the impedance in the shunt circuit increases and a constant level that is not dependent on the length of line is obtained in the local exchange when sending and in the receiver when receiving. All semiconductor elements for the microphone and receiver and for transmission regulation, as well as the majority of the required resistances, are assembled in one monolithic circuit. The monolithic circuit and the required capacitors are mounted on a thick film substrate, utilizing the possibilities offered by the thick film network for trimming to the nominal amplification and for adaptation to different current feed systems. The transmission circuit is encapsulated in polyuretane, chosen for its good resistance to temperature variations. The size of the complete unit is 7x20X35 mm. The transmission circuit is also electrically protected against transients by an external 15 V zener diode. IMPULSING UNIT Circuit components It was necessary to integrate many of the various functions of the impulsing unit. Fig. 17 shows a block diagram of the unit. The only discrete components used are capacitors and the diodes and resistors that could not be integrated in the blocks to which they belong, for example because of high precision requirements. The impulsing unit is protected against fast transients by a 100 V zener diode. Functional description The memory circuit with the associated logic, V1, is built up around a 4- phase dynamic shift register having a capacity of 20 figures. Two of the four clock pulses (01 and 03) come from the clock and control circuit V4, and the other two (02 and 04) are generat-
127 ed internally in V1. The logic levels are 0 and —4 V. The number information from the pushbutton set comes in on inputs P1—P4, and at the same time the common contact of the set gives a control signal to the anti-bounce logic via P5. The anti-bounce protection consists of a 5 ms delay before the number code is accepted for decoding and verification. The output of pulses starts immediately after the first digit has been accepted. A special register (marker) checks that the digits are fed out in the right order. The output signals consist of a control signal to the switch that disconnects the transmission circuit, and trigger signals to the impulsing switch. All the relevant frequencies and breakmake ratios can be obtained by external strapping. The oscillator, 10, oscillates at 4 V at a frequency of 18 kHz. It provides both trigger signals to 12 for the clock pulses 01 and 03, and for feeding the cascade generator, 11. The cascade generator is a diode capacitance ladder, which transforms 4 V a.c. to 15 V d.c. for feeding the clearing and pulse shaping circuit. The clearing and pulse shaping circuit, 12, gives the 15 V clock pulses with rapid rise and decay times that the memory unit requires. It also contains a clearing circuit that initially clears the memory of all the (probably erroneous) information that the circuit may have recorded before the operating voltage reached its set value (12.5 V). This ensures that the information fed into the memory is correct. The line adaptation circuit, 6, consists of transistor switches that disconnect the transmission circuit and which also impulse. The transmission switch is normally conducting. In its cut-off state the impulsing switch conducts sufficiently to maintain a certain charge on the capacitor that drives the oscillator during the impulsing and to make the transmission switch conducting. This "leakage" across the line takes up to about 1 mA of the line current. From an a.c. point of view the line is thereby shunt- Fig. 17 Impulsing unit. Block diagram 1. Contact bounce logic 2. Output logic 3. Input decoder 4. Shift register 4x20 bits 5. Secondary frequency divider 6. Line adaptation circuit 7. Check register 8. Control logic 9. Primary frequency logic and inter-digit pause logic 10. RC oscillator 11. Cascade generator 12. Zero setting and pulse shaping circuit 13. Transmission circuit
Page 1: ERICSSON REVIEW 3 1976 GEOSTATIONAR
Page 4 and 5: Geostationary Telecommunications Sa
Page 6 and 7: 112 forever silent. The next launch
Page 8 and 9: 114 Figs. 1—4 Figs. 5—8
Page 10 and 11: 116 Figs. 17—20 Figs. 21—24
Page 12 and 13: Electronic Push-button Telephone Se
Page 14 and 15: The bottom part (frame) ot the set
Page 16 and 17: Fig. 10 Buzzer unit Fig. 9 Tone rin
Page 18 and 19: Fig. 12 Impulsing unit and ring uni
Page 22 and 23: 128 ed by about 100 kohms. In order
Page 24 and 25: Fig. 20 DC characteristics (speech
Page 26 and 27: 132 use a microphone in which the o
Page 28 and 29: CCM - A Well- tried and Economic Ma
Page 30 and 31: 136 ] Do not allow more staff in th
Page 32 and 33: Ten Years Experience of CCM in the
Page 34 and 35: 140 Table 2 Existing staff requirem
Page 36 and 37: Optimization of Power Supply Equipm
Page 38 and 39: 144 Initial expenditure. This consi
Page 40 and 41: Table 1 Acquisition costs for diffe
Page 42 and 43: 148 Fig. 8 Instead of feeding the p
Page 44 and 45: 150 Fig. 10 Apart from a highly sta
Page 46 and 47: Development, Production and Mainten
Page 48 and 49: 154 combined to meet the needs of e
Page 50 and 51: 156 duction and putting the package
Page 52 and 53: 158 Fig. 5 Working procedure when p
Page 54 and 55: 160 The error message is sent from
Page 56 and 57: Dr. Christian Jacobceus chaired the
Page 58 and 59: 164 Among the reasons that were giv
Page 60: TELEFONAKTIEBOLAGET LM ERICSSON PRI

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