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PBL386212QNT Datasheet(PDF) 10 Page - Ericsson |
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PBL386212QNT Datasheet(HTML) 10 Page - Ericsson |
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10 / 16 page  PBL 386 21/2 10 Functional Description andApplications Informa- tion Transmission General A simplified ac model of the transmission circuits is shown in figure 8. Circuit analysis yields: (1) (2) V TR = EL - IL · ZL (3) where: V TX is a ground referenced version of the ac metallic voltage between the TIPX and RINGX terminals. G 2-4S is the programmable SLIC two-wire to four-wire gain (transmit direction). See note below. V TR is the ac metallic voltage between tip and ring. E L is the line open circuit ac metallic voltage. I L is the ac metallic current. R F is a fuse resistor. R P is part of the SLIC protection. Z L is the line impedance. Z T determines the SLIC TIPX to RINGX impedance at voice frequencies. Z RX controls four- to two-wire gain. V RX is the analog ground referenced receive signal. V Z V Z I TX T RX RX L RSN += α α RSN is the receive summing node current to metallic loop current gain = 200. Note that the SLICs two-wire to four-wire gain, G 2-4S, is user programmable between two fix values. Refer to the datasheets for values on G 2-4S. Two-Wire Impedance To calculate Z TR, the impedance presented to the two-wire line by the SLIC including the fuse and protection resistors R F and RP let: V RX = 0. From (1) and (2): Thus with Z TR, αRSN, G2-4S, RP and RF known: Two-Wire to Four-Wire Gain From (1) and (2) with V RX = 0: Four-Wire to Two-Wire Gain From (1), (2) and (3) with E L = 0: For applications where Z T/(αRSN·G2-4S) + 2RF + 2RP is chosen to be equal to Z L the expression for G4-2 simplifies to: Four-Wire to Four-Wire Gain From (1), (2) and (3) with E L = 0: Hybrid Function The hybrid function can easily be implemented utilizing the uncommitted amplifier in conventional CODEC/filter combinations. Please, refer to figure 9. Via impedance Z B a current proportional to VRX is injected into the summing node of the combination CODEC/filter amplifier. As can be seen from the expression for the four-wire to four-wire gain a voltage propor- tional to V RX is returned to VTX. This voltage is converted by R TX to a current flowing into the same summing node. These currents can be made to cancel by letting: The four-wire to four-wire gain, G 4-4, includes the required phase shift and thus the balance network Z B can be calculated from: When choosing R TX, make sure the output load of the VTX terminal is >20 k Ω. If calculation of the Z B formula above yields a balance network containing an inductor, an alternate method is recommended. Contact Ericsson Micro- electronics for assistance. The PBL 386 21/2 SLIC may also be used together with programmable CODEC/ filters. The programmable CODEC/filter allows for system controller adjustment of Figure 8. Simplified ac transmission circuit. G Z ZG T RX S 42 24 1 2 − − =− ⋅ V R V Z E TX TX RX B L += = 00 () PBL 386 21/2 + - + - VTX RSN I L /αRSN TIPX RINGX + - EL + - TIP RING RF RF ZTR ZT VTX VRX ZRX IL IL RHP + - ZL VTR RP G 2-4S RP V V G IR R TR TX S LF P =+ ⋅ + − 24 22 () Z Z G RR TR T RSN S FP = ⋅ ++ − α 24 22 ZG Z R R T RSN S TR F P =⋅ ⋅ − − − α 24 22 () G V V Z Z Z Z GZ R R TR RX T RX L T RSN SL F P 42 24 22 − − == −⋅ +⋅ + + α () G V V Z Z G RR TX TR T RSN T RSN S FP 24 24 22 − − == ⋅ ++ / α α G V V Z Z GZ R R Z GZ R R TX RX T RX SL F P T RSN SL F P 44 24 24 22 22 − − − == −⋅ ⋅+ + +⋅ + + () () α ZR V V R Z Z Z GZ R R GZ R R BTX RX TX TX RX T T RSN SL F P SL F P =− ⋅ = ⋅⋅ +⋅ + + ⋅+ + − − α 24 24 22 22 () () |
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