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BL1062A1
Low voltage transmission circuits with dialer interface
1. GENERAL DESCRIPTION The BL1062A1 is integrated circuits that perform all speech and line interface functions required in fully electronic telephone sets. It performs electronic switching between dialling and speech. The ICs operate at line voltage down to 1.6 V DC (with reduced performance) to facilitate the use of more telephone sets connected in parallel. BL1062A1 improves the EMC performance in-circuit that can enhance the telephone sets' EMC. 2. FEATURES Low DC line voltage; operates down to 1.6 V (excluding polarity guard) Voltage regulator with adjustable static resistance Provides a supply for external circuits Symmetrical high-impedance inputs (64 ) for dynamic, magnetic or piezoelectric microphones Asymmetrical high-impedance input (32 ) for electret microphones DTMF signal input with confidence tone Mute input for pulse or DTMF dialling, active LOW (MUTE) Receiving amplifier for dynamic, magnetic or piezoelectric earpieces Large gain setting ranges on microphone and earpiece amplifiers Line loss compensation (line current dependent) for microphone and earpiece amplifiers Gain control curve adaptable to exchange supply DC line voltage adjustment facility Enhanced EMC performanc 3. BLOCK DIAGRAM
Fig. 1 Block Diagram
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BL1062A1
4. Pin Configurations, Definitions SYMBOL PIN DESCRIPTION LN 1 positive line terminal GAS1 2 gain adjustment; transmitting amplifier GAS2 3 gain adjustment; transmitting amplifier QR 4 non-inverting output; receiving amplifier GAR 5 gain adjustment; receiving amplifier 6 Inverting microphone input MI- MIC+ 7 non-inverting microphone input NC 8 NC VEE 9 Negative line terminal IR 10 Receiving amplifier input DTMF 11 dual-tone multi-frequency input MUTE 12 mute input (see note 1) VCC 13 positive supply decoupling REG 14 voltage regulator decoupling AGC 15 automatic gain control input SLPE 16 slope (DC resistance) adjustment
5.
Function Description
Power for the IC and its peripheral circuits is usually obtained from the telephone line. The
Supplies VCC , LN, SLPE, REG
supply voltage is derived from the line via a dropping resistor and regulated by the IC. The supply voltage
VCC
may also be used to supply external circuits e.g. dialling and control circuits.
Decoupling of the supply voltage is performed by a capacitor between VCC and VEE . The internal voltage regulator is decoupled by a capacitor between REG and VEE . The DC current flowing into the set is determined by the exchange supply voltage Vexch, the feeding bridge resistance Rexch and the DC resistance of the telephone line Rline . At line currents below 9 mA 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 (2 x 32 k) and its voltage gain is typically 52 dB (when R7 = 68 k, see Figures 2 and 3). Dynamic, magnetic, piezoelectric 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.
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BL1062A1
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. Dual-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) 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). 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 network attenuation (32 dB) from the amplifier gain. 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. Automatic Gain Control input AGC Automatic line loss compensation is achieved by connecting a resistor (R6) between AGC and VEE . The automatic gain control varies the gain of the microphone amplifier and the receiving amplifier in accordance with the DC line current. The control range is 5.8 dB which corresponds to a line length of 5 km for a 0.5 mm diameter twisted-pair copper cable with a DC resistance of 176 /km and average attenuation of 1.2 dB/km). Resistor R6 should be chosen in accordance with the exchange supply voltage and its feeding bridge resistance. The ratio of start and stop currents of the AGC curve is independent of the value of R6. If no automatic line-loss compensation is required the AGC pin may be left open-circuit. The amplifiers, in this condition, will give their maximum specified gain. Enhanced EMC performance The input pins BL1062A1 is added RC filters to improve the EMC performance, so the telephone sets which used BL1062A1 are easily to handle the EMC design. LIMITING VALUES SYMBOL PARAMETER VLN positive continuous line voltage VLN(R) repetitive line voltage during switch-on or line interruption VLN(RM) repetitive peak line voltage for a 1 ms pulse per 5 s Iline line current Ptot total power dissipation Tamb operating ambient temperature Tstg storage temperature
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CONDITIONS
MIN. - - - - - -25 -40
MAX. 12 13.2 28 140
UNIT V V V mA mW o C o C
R9 = 20 ; R10 = 13 ; see Fig.6 R9 = 20 R9 = 20
600
+75 +125
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BL1062A1
6. CHARACTERISTICS MAX. UNIT V V 4.25 6.5 Iline = 11 to 140 mA; VEE = 0 V; f = 800 Hz; Tamb =25 oC; unless otherwise specified. SYMBOL PARAMETER CONDITIONS MIN. TYP. VLN voltage drop over MIC inputs open-circuit circuit between LN Iline = 1 mA 1.6 Iline = 4 mA and VEE 1.9 Iline = 15 mA 3.55 4.0 4.9 5.7 Iline = 100 mA Iline = 15 mA; VLN Voltage drop over circuit bewteen LN 3.5 RVA(LN to REG)=68K and VEE 4.5 RVA(LN to SLPE)=39K ICC supply current VCC = 2.8 V - 0.9 VCC supply voltage Iline = 15 mA; available for MUTE = LOW Ip = 1.2 mA 2.2 2.7 peripheral circuitry MUTE = LOW Ip = 0 mA 2.5 3.4
1.35 4.5 3.8
mA V V V V K
|Zi|
CMRR Gv MIC Gvf
GvT
|Zi| Gv DTMF Gvf
GvT
VLN(rms) |Zi|
Gv Gvf
GvT
Vo(rms)
Input impedance between MIC- and MIC+ Common mode rejection ratio voltage gain MIC+ or MIC- to LN Gain variation with frequency reference to 800Hz Gain variation with temperature reference to 25 Input impedance of DTMT voltage gain from DTMF to LN Gain variation with frequency reference to 800Hz Gain variation with temperature reference to 25 output voltage (RMS value) Input impedence of receiving amplifier voltage gain from IR to QR Gain variation with frequency reference to 800Hz Gain variation with temperature reference to 25 output voltage (RMS value)
Between MIC- and MIC+
64
82 Iline = 15 mA; R7 = 68 k Iline = 100 mA; R7 = 68 k F=300 and 3400 Hz 50.5 44.0 52.0 45.5 0.2 54.5 47.0
dB dB dB dB
Without R6;Iline=50mA; Tamb=25 and +75
0.2
dB
20.7 Iline = 15 mA; R7 = 68 k F=300 and 3400 Hz 24.0 25.5 0.2 27.0
K dB dB
Without R6;Iline=50mA; Tamb=25 and +75 THD = 10% Iline = 15 mA 1.7
0.2
dB
2.3 21
-
V K
Iline = 15 mA; RL = 300 Iline = 100 mA; RL = 300 F=300 and 3400 Hz
29.5 24.5
31 26 0.2
32.5 27.5
dB dB dB
Without R6;Iline=50mA; Tamb=25 and +75 THD = 2%; sine wave drive; R4 = 100 k; Iline =15 mA; Ip =0 mA RL = 150 RL = 450
-4-
0.2
dB
0.22 0.3
0.33 0.48
- -
V V
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BL1062A1
Vo(rms) GV GV GV output voltage (RMS value) MIC- or MIC+ to LN Voltage gain from DTMT to QR Controlling the gain from IR to QR and the gain from MIC+,MIC- to LN gain control range Hightest line current for maximum gain Lowest line current for maximum gain THD = 10%; R4 = 100 k; Iline =15 mA; RL = 150 MUTE=Low R4=100k; RL=300 MUTE=Low R6=110k (bewteen AGC and VEE) Iline=70mA 15 70 -17 -5.8 V dB dB dB
IlineH
23
mA
IlineL
61
mA
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BL1062A1
Fig2 Test circuit for defining BL1062A1 voltage gain of MIC+, MIC- and DTMF inputs
Fig3 Test circuit for defining BL1062A1 voltage gain of receiving amplifier
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BL1062A1
7. APPLICATION CIRCUITS
Fig4 Typical application of BL1062A1
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