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PBL388121SO Datasheet(PDF) 6 Page - Ericsson |
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PBL388121SO Datasheet(HTML) 6 Page - Ericsson |
6 / 10 page PBL 388 12 6 Figure 6. Receiver and transmitter channel input arrangement. Figure 5. Passive networks setting the speech control function. Functional Description Speech control section Transmitter and Receiver Channels The transmitter and receiver channels consist of three amplifying stages each, F1, F2, F3 and F4, F5, F6. The inputs of the amplifiers must be ac. coupled because they are dc. vise at the internal reference voltage ( ≈2V) level. F1 and F4 are fixed gain amplifiers of 30,5 dB and 15.5 dB respectively, while the rest of them are of controlled gain type.The gain of F2, F3 as well as F5 and F6 is controlled by comparators. The comparator receives its information partly from the summing point of the transmitter, receiver and backgro- und noise detectors at CMP input and partly through the control input, CTR, which controls the gain dynamics (25 or 50 dB). Amplifiers F2 and F3 have the maximum gain when the transmitter channel is fully open, consequently the amplifiers F5 and F6 will have minimum gain and vice versa. See figure 5 and figure 11. The positive input on transmitter and the negative input on receiver channel has a rather high input impedance. It renders a good gain precision and noise performance when used with low signal source impedance. The differential input of the transmitter channel can be used to suppress unwanted signals in the microphone supply, see figure 7. Also see application 1. Signal Detectors and Comparator The signal detectors sense and rectify the receiver and microphone signals to opposite polarities referenced to the internal reference voltage of approx. 2V. The voltage at RxDet will go positive and at TxDet negative in the presence of a signal at the respective channel input. In the idle (no signal) state, the voltages at RxDet ,TxDet and CMP are equal to the internal reference voltage. Signal at Txin will result in an decreasing level at TxDetout and hence also at CMP input. R5 C3 C1 C2 C4 F2 F3 F1 PBL 388 12 1 5 15 4 2 3 87 9 10 + - + CTR CMP V+ N Det Rxout Rxin TxDet RxDet -Txin + Txin Txout 12 14 F6 F5 Control F4 + Ref. 13 11 6 GND 16 + + F1 F4 2 3 14 F5 + + F2 VRxin VTxin 100k 3k 100k 120k 120k 20k Tx Ref. I ~ 16 3k PBL388 12 ~ Rx |
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