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PBL3853 Datasheet(PDF) 7 Page - Ericsson |
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PBL3853 Datasheet(HTML) 7 Page - Ericsson |
7 / 16 page PBL 3853 7 Transmitter Amplifier The transmitter consists of two stages. The output of the transmitter drives a signal with adjustable impedance into the line. The signal at pin 1 (positive line) is 180 degrees out of phase with the signal at pin 2 from where the side tone compensation signal is taken. The transmitter has two inputs. An input at pin 5, where both active impedance and DC-characteristic can be adjusted. Another input at pin 3, which is the microphone signal input, where the filter for the transmitter frequency characteristic is placed. Pin 3 is at the same time used as a summing point to all other audio signals that are transmitted into the line (DTMF tones, hands free signal...). See figure 4. Receiver Amplifier The receiver gets its input signal from the summing point where the side tone cancellation takes place. The output drives single sided a low Ω (150 Ω) acoustical transducer. Diodes for absorbing acoustical shock must be provided externally. The amplifier has two inputs. One of them can be regulated with line length, the other has fixed unity gain. The latter can be used to cut off the receiver by forcing the input positive and is also useful for injecting the DTMF confidence tone into the receiver. The receiver amplifier is powered from the regulated DC-supply at pin 18. Figure 8. Fixed gain and line length regulation. Connecting the pin 6 to ground disables the line length regulation in the high gain mode, whereas setting the pin 6 on 1.2 V dc level or higher disables the line length regulation in low gain mode. Microphone Amplifier The microphone amplifier is primarily designed to be used with dynamic or magnetic microphones but can be used with buffered elctret microphones as well. The input of the amplifier is balanced for good CMRR. The gain of the amplifier can be regulated with the line length. The microphone amplifier has a mute input of its own. Pin 10. It is possible to use the microphone amplifier as a limiter (added to the limiter in the transmitter output stage) of the transmitted signal. The positive output swing is then limited by the peak output current of the microphone amplifier. The negative swing is limited by the saturation voltage of the output amplifier. The output of the amplifier is DC-wise at internal reference level (1.2 V). The lowest negative level for the signal is reference minus one diode and sat.transistor drop. (1.2-0.6-0.1=0.5 V). The correct clipping level is found by determining the composite AC- and DC- load that gives a maximum symmetrical unclipped signal at the output. This signal is then fed into the transmitter amplifier at a level that renders a symmetrical signal clipping on the line (adjust with ratio R 3, R4). The total transmitter gain can then be adjusted with the load of the electret microphone buffer amplifier. See figure 9. Figure 10. Common receiver and transmitter mute arrangement. Figure 11. Microphone solutions. Figure 9. Microphone amplifier output clipping, level. PBL3853 5 4 6 15k 10k + + 1.2V 2.5k 8.77k + 1.2V 7.5k 13k 15k 37.5k 45k I=0.3mA Circuit supply to gain reg. with line length ( ≈ 6dB) VX VF + RC RD R1 C3 Line 11 PBL 3853 C4 R3 DC- load R4 AC- load RDTMF TI Z DTMF Z Powerful cc gen Valid when no C4 is used. DC-load=R3+R4 R3+R4>6k AC-load=R3+R4// (R +Z ) //Z TI DTMF DTMF DC (ref. ≈1.2V) ref.-diod ≈0.5V PBL 3853 18 10 17 DTMF in 11 12 13 Dynamic mic. PBL 3853 + - M a) 11 12 13 2x50k Extended low voltage/ current operation + - M PBL 3853 c) 11 12 13 4 PBL 3853 d) + - M 11 13 PBL 3853 e) + - M 12 DC C 11 12 13 4 R If balanced mic.is used an additional RC link is recomm. if pin 4 is used as supply PBL 3853 f) + - M 11 12 13 Magnetic mic. PBL 3853 + - M b) |
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Similar Description - PBL3853 |
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