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SL1062A bảng dữ liệu(PDF) 3 Page - System Logic Semiconductor |
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SL1062A bảng dữ liệu(HTML) 3 Page - System Logic Semiconductor |
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3 / 9 page  SL1062A System Logic Semiconductor SLS Vref is an internally generated temperature compensated reference voltage of 3.7 V and R9 is an external resistor connected between SLPE and VEE. In normal use the value of R9 would be 20 Ω. Changing the value of R9 will also affect microphone gain, DTMF gain, gain control characteristics, sidetone level, maximum output swing on LN and the DC characteristics (especially at the lower voltages). Under normal conditions, when ISLPE>>ICC + 0.5 mA + Ip, the static behaviour of the circuit is that of a 3.7 V regulator diode with an internal resistance equal to that of R9. In the audio frequency range the dynamic impedance is largely determined by R1. Fig.2 shows the equivalent impedance of the circuit. Leq = C3 x R9 x RP RP = 16.2 K Ω Figure 2. Equivalent impedance circuit At line currents below 9mA the internal reference voltage is automatically adjusted to a lower value (typically 1.6 V at 1 mA) This means that more sets can be operated in parallel with DC line voltages (excluding the polarity guard) down to an absolute minimum voltage of 1.6 V. At line currents below 9 mA the circuit has limited sending and receiving levels. The internal reference voltage can be adjusted by means of an external resistor (RVA). This resistor when connected between LN and REG will decrease the internal reference voltage and when connected between REG and SLPE will increase the internal reference voltage. Microphone inputs MIC+ and MIC- and gain pins GAS1 and GAS2 The circuit has symmetrical microphone inputs. Its input impedance is 64 K Ω (2 x32 KΩ) and its voltage gain is typically 52 dB (when R7 = 68 K Ω, see Figure 3). Dynamic, magnetic, piezo-electric or electret (with built-in FET source followers) can be used. The gain of the microphone amplifier can be adjusted between 44 dB and 52 dB to suit the sensitivity of the transducer in use. The gain is proportional to the value of R7 which is connected between GAS1 and GAS2. Stability is ensured by two external capacitors, C6 connected between GAS1 and SLPE and C8 connected between GAS1 and VEE. The value of C6 is 100 pF but this may be increased to obtain a first- order low-pass filter. The value of C8 is 10 limes the value of C6. The cut-off frequency corresponds to the time constant R7 x C6. Input MUTE When MUTE is LOW or open circuit, the DTMF input is enabled and the microphone and receiving amplifier inputs are inhibited. The reverse is true when MUTE is HIGH, MUTE switching causes only negligible clicking on the line and earpiece output. If the number of parallel sets in use causes a drop in line current to below 6 mA the DTMF amplifier becomes active independent to the DC level applied to the MUTE input. Dial-tone multi-frequency input DTMF When the DTMF input is enabled dialling tones may be sent on to the line. The voltage gain from DTMF to LN is typically 25.5 dB (when R7 = 68 K Ω) and varies with R7 in the same way as the microphone gain. The signalling tones can be heard in the earpiece at a low level (confidence tone). Receiving amplifier IR, QR and GAR The receiving amplifier has one input (IR) and a non- inverting output (QR). The IR to QR gain is typically 31 dB (when R4 = 100 K Ω). It can be adjusted between 20 and 31 dB to match the sensitivity of the transducer in use. The gain is set with the value of R4 which is connected between GAR and QR. The overall receive gain, between LN and QR, is calculated by subtracting the anti-sidetone netwo rk attenuation (32 dB) from the amplifier gain. Two external capacitors, C4 and C7, ensure stability. C4 is normally 100 pF and C7 is 10 times the value of C4. The value of C4 may be increased to obtain a first- order low-pass filter. The cut-off frequency will depend on the time constant R4 x C4. The output voltage of the receiving amplifier is specified for continuous-wave drive. The maximum output voltage will be higher under speech conditions where the peak to RMS ratio is higher. |
Số phần tương tự - SL1062A |
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Mô tả tương tự - SL1062A |
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