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PBL388131SO Datasheet(PDF) 6 Page - Ericsson |
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PBL388131SO Datasheet(HTML) 6 Page - Ericsson |
6 / 16 page 6 PBL 388 13 Figure 8. Receive and transmit channel input arrangement. Figure 7. Passive networks setting the speech control function. R5 C3 C1 C2 C4 + F2 F3 – F1 PBL 388 13 22 21 24 4 15 19 3 1 2 7 6 8 9 23 16 17 18 20 + - + CTR CMP GND -C V+ N Det Rxout xin + R xin TxDet RxDet LSPin RE R DC -Txin + Txin Txout -R 11 13 14 F6 F5 Control F4 + LSP +L Ref. VOL 12 10 5 + + + F1 F4 1 2 13 14 F5 + + F2 VRxin VTxin 100k 3k 100k 120k 120k 20k Tx Ref. I ~ 16 3k 20k PBL388 13 ~ Rx 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 29.5 dB and 15.5 dB respectively, while the rest of them are of controlled gain type amplifiers.The gain of F2, F3 as well as F5 and F6 is controlled by the comparator. Ac. loading the channel outputs F3 and F6 will lessen the dc. current consumption, maximum load 10 k Ω. The output capacity can be increased somewhat in case needed, by coupling a 10 k Ω resistor from the respective output pin directly to ground (before the optional capacitor).The comparator receives its in- formation from the summing point of the transmitter, receiver and background noise detectors at CMP input. The control input CTR, controls the gain dynamics (25 or 50 dB). Amplifiers F2 and F3 have the maxi- mum gain when the transmitter channel is fully open, consequently the amplifiers F5 and F6 will have minimum gain and vice versa. See figure 7 and figure 13. The positive input on each channel has a high input impedance. It renders a good gain precision and noise performance when used with low impedance signal source . The negative input of the receiver channel should be returned to ground with a capacitor. The differential input of the transmitter channel can be used to sup- press unwanted signals in the microphone supply, see figure 9. Also see application. Signal Detectors and the 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 a decreasing level at TxDetout and hence also at CMP input. |
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