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PBL 385 82 December 1999
PBL 38582 Telephone Line interface circuit for DECT, DAM, CT Unisolated or Isolated
Description
PBL 38582 is a monolithic bipolar integrated circuit for use as telephone line interface in unisolated or isolated DECT and other cordless telephone residential base stations and in analog / digital answering machines or as second line in an unisolated DECT telephone base station. Transmit and receive gains are set by external components. On / Off switchable gain, related to line, regulation for different current feeds can be set by external resistors. Typical current feeds as 48 V, 2 * 200 ohm, 48 V 2 * 400 ohm and 60 V 2 * 600 ohm can be handled. Application dependent parameters such as line balance, impedance to the line and frequency response are set by external components. Parameters are set independently which results in an easy adoption for various market needs.
Key Features
* Minimum number of inexpensive external components, 5 capacitors and 4 resistors. * Current range 5 - 130 mA(DIL), 5 - 100 mA(20-pin SO) 5 - 70 mA(16-pin SO) 385 82/2 * Operation voltage range down to 2 V. * Short start-up time.
P
B
L
3
8
5
8
1
PBL 38582
Fast start - up
P
B
L
18
38
20-pin plastic SO
DC supply
+ 6 3 2
15 5, 14,16
RECEIVE
Reference
17
Limiter
5
4
1 2
TRANSMIT
P
B
18-pin plastic DIP
Figure 1. Functional diagram. DIP package.
L
38
Telephone line
58
2
82
2
16-pin plastic SO
1
PBL 385 82
Maximum Ratings
Parameter Symbol Min Max Unit
Line voltage, tp = 2 s Line current, continuous DIP Line current, continuous SO-20 package Line current, continuous SO-16 package Operating temperature range Storage temperature range No input should be set on higher level than pin 15.(+C)
VL IL IL IL PBL 38582/2 TAmb TStg
0 0 0 0 -40 -55
18 130 100 70 +70 +125
V mA mA mA C C
R = 0-4k L 0 ohm when artificial line is used 5H+5H
310
+
R feed = 400+400 C
ARTIFICIAL LINE
IL
+ LINE
350
V4 output
Receiver
+
E = 48.5V
V2
600
V
L
PBL 38582 with external components See fig. 4
V1
V3
Transmitter input
C = 1F when artificial line is used 470F when no artificial line
- LINE
Figure 2. Test set up without rectifier bridge.
5H+5H R
RL = 0 - 4 k
Uz= 15-16V
IL
310
+ LINE
350 PBL 38582 with external components See fig. 4 Transmitter input
+
feed = 400+400
1F V2
600
V4 output
Receiver
+
E = 50.0V
V
L
V1
- LINE
V3
Figure 3. Test set up with rectifier bridge.
1
+Line
PBL 38582
Fast start - up
18
Receiver output
17
Limiter
Reference
DC supply
+
6
3 C3
2
15
5, 14,16 C4
4
Figure 4. Circuit with external components for test set up. R1 = 6.2 k R2 = 62 k R6 = 75 R3 = 909 R14 = 10k C1 = 68 F C2 = 15 nF C3 = 0.1F C4 = 47 nF DIP package pinning.
Transmitter input
R13 R14 R6
R1
R2 R3 C2 C1
-Line
2
PBL 385 82
Electrical Characteristics
At TAmb = + 25 C. No cable and no line rectifier unless otherwise specified. IL = 100 mA is not valid for 16-pin SO package.
Parameter Ref.fig. Conditions Min Typ Max Unit
Line voltage, VL Transmitting gain Transmitting frequency response Transmitter dynamic output
2 2
IL = 15 mA IL = 100 mA 20 *10 log (V2 / V3); 1 kHz 200 Hz to 3.4 kHz
3.3 11 24 -1
3.7 13 25
4.1 15 26 1
V V dB dB
2
2
200 Hz - 3.4 kHz 2% distortion, IL = 20 - 100 mA
1.5
Vp Vp dB Psof 20.5 kohm
Transmitter maximum output
2
200 Hz - 3.4 kHz IL = 0 - 100 mA, V3 = 0 - 1 V
3
Transmitter output noise Transmitter input impedance pin 3 Receiving gain Without gain regulation Receiving gain With gain regulation
2 2
Psof-weighting, Rel 1 Vrms, RL = 0 1 kHz 13.5
-75 17
20 * 10 log (V4 / V1); 1 kHz 2 2 2 2 RL = 0 - xxx ohm, R11= 10k 20 * 10 log (V4 / V1); 1 kHz, R11 not used RL = 0 ohm, RL = 400 ohm RL = 900 ohm - 2.2 kohm 1 kHz, RL = 0 to 900 ohm 200 Hz to 3.4 kHz 1 kHz, without 310 resistor 200 Hz - 3.4 kH 2% distortion, IL = 20 - 100 mA 3 Measured with line rectifier 200 Hz - 3.4 kHz, IL = 0 - 100 mA, V1= 0 - 50 V 0.9 Vp -18.5 -16 -13.5 3 -1 3 0.5 -16.5 -14 -11.5 5 -14.5 -12 -9.5 7 1 dB dB dB dB dB ohm Vp -18.5 -16.5 -14.5 dB
Receiving range of regulation Receiving frequency response Receiver output impedance Receiver dynamic output note 1 Receiver maximum output
2 2 2 2
Receiver output noise
2
A-weighting, Rel 1Vrms, with cable 0 - 5 km, O = 0.5 mm, 0 - 3 km, O = 0.3 mm
-85
dB A
Notes: 1. The dynamic output can be nearly doubled if the 310 series resistor is omitted.
3
PBL 385 82
+L 1 TO 2 TI 3 +C 4 -L 5 GR
6
18 17 16 15 14 13 12 11 10
RE 2 RE 1 -L RI -L NA NA NA NA
+L 1 TO 2 TI 3 +C 4 -L 5 GR 6 NA 7 NA 8 NA NA
9 10 20 19 18 17 16 15 14 13 12 11
RE2 RE1 -L RI -L NA NA NA NA NA
+L 1 TO 2 TI 3 +C 4 -L 5 GR 6 NA 7 NA 8
16 15 14 13 12 11 10 9
RE2 RE1 -L RI -L NA NA NA
NA 7 NA 8 NA 9
18-pin DIP
20-pin SO
16-pin SO
Figure 5. Pin configuration.
Pin Descriptions
Refer to figure 5. DIP 1 2 SO 20 SO 16 1 2 1 2 Name +L TO Function Output of the transmitter amplifier. Connected to the line through a polarity guard diode bridge. Output of the transmitter amplifier. Connected through a resistor of 47 to 100 ohm to -L. Sets the DC-charateristic of the circuit.The output has a low AC output impedance and the signal is used to drive a side tone balancing network. Input of transmit amplifier. Input impedance 17 k 20 %. The positive power supply terminal for most of the circuitry inside the PBL 385 82 (about 1 mA current consumption). The +C-pin is to be connected to a decoupling capacitor of 47 F to 150 F. The control input for the gain regulation in the receiver.
3 4
3 4
3 4
TI +C
6 5 14 16 15 17 18 7 8 9 10 11 12 13
6 5 16 18 17 19 20 7 8 9 10 11 12 13 14 15 4
6 5 12 14 13 15 16 7 8 9 10 11
GR -L RI RE2 RE1 NA NA NA NA NA NA NA NA NA
} }
The negative power terminal, connected to the line through a polarity guard diode bridge. Input of the receive signal amplifier. Input impedance is 38 kohm 20 %. The receive signal amplifier outputs. Output impedance is approximately 3 ohm.
PBL 385 82
Functional description
Design procedure; ref. to fig.4. The design is made easier through that all settable parameters are returned to ground (-line), this feature differs it from bridge type solutions.To set the parameters in the following order will result in that the interaction between the same is minimized. 1. Set the circuit impedance to the line, either 600 or complex. (R3 and C1). C1 should be big enough to give low impedance compared with R3 in the telephone speech frequency band.Too large C1 will make the start-up slow. See fig. 10. 2. Set the DC-characteristic that is required in the PTT specification or in case of a system telephone,in the PBX specification (R6).There are also internal circuit dependent requirements like supply voltages etc. 3. Set the attac point where the line length regulation ( if used ) is supposed to cut in. Note that in some countries the line length regulation is not allowed. In most cases the end result is better and more readily achieved by using the line length regulation (line loss compensation) than without. 4. Set the transmitter gain and frequency response. 5. Set the receiver gain and frequency response. See text how to limit the max. swing. 6. Adjust the side tone balancing network if used.The network in most cases is just a coarse resistive divider to take care of the first order of balancing. The fine balancing is done by the DSP in the system. 7. Set the RFI suppression components in case necessary. 8. Circuit protection. Apart from any other protection devices used in the design a good practice is to connect a 15V 1W zener diode across the circuit , from pin 1 to -Line.
+Line 1 4 a) b) 220 R3 820 C c)
PBL 38 582
3
2 Rs 1 + C1 Example: How to connect a complex network. 220+820//C -Line
C2
R6
Figure 6. AC-impedance.
is dependent on the temperature and the quality of the component will cause some of the line signal to enter pin 4. This generates a closed loop in the transmitter amplifier that in its turn will create an active impedance thus lowering the impedance to the line. The impedance at high frequencies is set by C2 that also acts as a RFI suppressor. In many specifications the impedance towards the line is specified as a complex network. See fig. 6. In case a). the error signal entering pin 4 is set by the ratio Rs/R3 (909), where in case b). the ratio at high frequencies will be Rs/220 because the 820 resistor is bypassed by a capacitor. To help up this situation the complex network capacitor is connected directly to ground, case c). making the ratio Rs/220+820 and thus lessening the error signal. Conclusion: Connect like in case c) when complex impedance is specified.
* *
DC - characteristic
The DC - characteristic that a telephone set has to fulfill is mainly given by the network administrator. Following parameters are useful to know when the DC behaviour of the telephone is to be set: * The voltage of the feeding system * The line feeding resistance 2 x....... ohms. * The maximum current from the line at zero line length. * The min. current at which the telephone has to work (basic function).
The lowest and highest voltage permissible across the telephone set. The highest voltage that the telephone may have at different line currents. Normally set by the network owners specification.The lowest voltage for the telephone is normally set by the voltages that are needed for the different parts of the telephone to function. For ex. for transmitter output amplifier, receiver output amplifier, dialler, speech switching. R6 will set the slope of the DC-char. and the rest of the level is set by some constants in the circuit as shown in the equation below. The slope of the DC-char. will also influence the line length regulation (when used ) and thus the gain of both transmitter and receiver. See the table under gain regulation. R6 also acts as power protection for the circuit, this must be kept in mind when low values of R6 are considered. See fig. 7.
Impedance to the line
The AC- impedance to the line is set by R3, C1 and C2. Fig.6. The circuits relatively high parallel impedance will not influence the line impedance to any noticeable extent.At low frequencies the influence of C1 can not be neglected. Series resistance of C1 that
VLine 2 + 1.5 R 6 Iline Vtelephoneline 1.5V + Vline
5
PBL 385 82
signal to the earphone and thus preventing an acoustical shock. A resistor in series with the output can very well be used to increase the protection level. Note, that the noise in the receiver is allways transmitter noise that has been more or less well balanced out by the side tone network. The RC - network (optional) at the output is to stabilize against the inductive load that an earphone represents.
V
16 14 12 10 8 6 4 2
V telephone line V line V pin 4
V pin 2
PBL 38 582
17
+
+ Rx -
(C) Z
I
20 40 60 80 100 120
L
18
Z (C) Z > 5k
mA
The capacitor C is optional
Figure 7. DC - characteristics.( R6 = 75 )
Figure 8. Unbalanced Rx loading.
Transmitter amplifier
The transmitter amplifier in PBL38582 consists of three stages. The first stage is an amplitude limiter for the input signal at TI, in order to prevent the transmitted signal to exceed a certain set level and cause distortion. The second stage amplifies further the signal from the first and adds it to a DC level from an internal DC-regulation loop in order to give the required DC characteristic to the telephone set. The output of this stage is TO. The third stage is a current generator that presents a high impedance towards the line and has its gain from TO to +L. The gain of this amplifier is ZL/R6 where ZL is the impedance across the telephone line. Hence, the absolute maximum signal amplitude that can be transmitted to the line undistorted is dependent of R6. (amplitude limiting) The transmitter gain is set by the analog (transmitter) signal from the passband circuit and the frequency response is set by the capacitors at input circuit at pin 3, the low end being influenced by C3 and the high end by C6. The input signal source impedance to the transmitter amplifier input TI should be reasonably low in order to keep the gain spread down.
Receiver amplifier
The receiver amplifier consists of three stages, the first stage being an input buffer that renders the input a high impedance. The second stage is a gain regulated differential amplifier and the third stage a balanced power amplifier. The power amplifier has a differential output with low DC- offset voltage, therefore a series capacitor with the load is normally not necessary. The receiver amplifier uses at max. swing 4-6 mA peak. This current is drawn from the +Line. The gain and frequency response is set at the input RI with a RC-network. The receiver gain can be regulated.The range of regulation from the input to the output is 5 2 dB (19 to 24dB). The balanced earphone amplifie can not be loaded to full (both current and signal level ) single ended.The signal would be distorded when returned to ground. A methode is shown in fig.8 how to connect a light load (5k ac. or DC wise) to the output. It is preferred that both outputs are loaded the same. The receiver has, as a principal protection, two series diodes anti parallel across its output to limit the
Gain regulation.
The receiver is gain regulated (line loss compensated). There is a fixed default compensation on the chip that can be adjusted or or set to constant high or low gain mode. The input impedance at the gain regulation pin 6 is 5.5k 20%. The default regulation pattern is valid when the input is left open. Fig. 9 shows a typical receiver gain pattern versus line length. The following will show, what to alter, to change the look of the curve. a). Adjustable with R12 for the receiver. b). The attack point of the regulatorcan be adjusted with resistors R13 or R14 to either direction, up or down, on the line current axis. c). The angle of elevation of the curve is mainly set by the value of R6. If the DCcharacteristics is set according to the line parameters and a correct value for R6 is chosen the angle is mostly correct but it can be adjusted with R6. The adjustement will affect the DC-characteristics as well as most of the other parameters. This is why the DC- characteristic is set early in the design phase.
6
PBL 385 82
dB
Battery feed Regulation: 48V, 2 * 200 48V, 2 * 400 48V, 2 * 800
R13
R14 180k
R6
c. b.
47 75 100
a. High limit
No regulation: Set for low gain All feedings Set for high gain Set for high gain 18k 22k <22k 47 - 100 47 75 - 100
I L
Low limit
Figure 9. Gain regulation principle.
What is balancing the side tone?
To understand that side tone balancing is to counteract the signal, that is transmitted via the microphone and transmitter to the line, returning to the earphone via the receiver. That presence of a strong side tone signal is disturbing in a way that one quite instictively lowers ones own voice level thus lowering the signal level for the other party. But again, if the balance is too good (seldom the case) the earphone will feel "dead". In practical terms what is expected is the same amplitude of ones own voice in the ear as when not talking in a telephone. The need to lower the side tone level
where no balancing has been done is in the order of 6 - 12 dB. To understand that the side tone is influenced by other factors like, the impedance of the line and the signal that enters the ear acoustically directly from the mouth and from the mouth through the material in the handset. The signal that enters the microphone from the earphone acoustically will also influence the return loss factor to the telephone line. To understand that the side tone network can be trimmed to form a veritable "distortion analyser", so that the distortion that is present from the microphone, will be the only signal entering the earphone and this signal even being small will sound very bad. It is better to induce some of the fundamental frequency back by making
the balance less perfect at that frequency. This is valid for a network that is trimmed to only one frequency. It is to strive to trim the network such that it will attenuate the fundamental and the harmonic frequencies alike throughout the different line combinations. To understand that if one of the two signals entering the balancing system from either direction, direct from microphone or via the line, is clipped, will result in a very distorted signal entering the receiver amplifier and thus the earphone. Further , to remember that side tone is a small signal that is the difference of two large signals and that the amplitude of the distortion can be up to ten times the amplitude of the fundamental frequency.
Telephone set side
Line side
a).
1
A short guidance for understanding the side tone principle. (See fig. 10.)
Assuming the line impedance to be 600. ( theorethical value ) Z1 = Line impedance Z2 = The telephone set impedance 600 Z1//Z2 = 300 R6 will have a certain value 39 - 100 to give the telephone a specified DCcharacteristic and overcurrent protection. Assuming that this DC-characteristic requires R6=60, hence it will be 1/5 of the Z1//Z2. This will in transmitting mode result that 1/5 of the ac-signal that is on the line to appear across R6.
PBL 385 82
17
Tx
2 15
Rx
18
b).
R7
Z2
Z1
c).
R8
R6 C5
}
R10
C4 R11
Zbal
R12
R9
Figure 10. The side tone suppression principle.
7
PBL 385 82
Note that the signals at points a. and b. are 180 degrees off phase. 10 x R6 R7 + Zbal Note #1 R7 Zbal Note#2 The ac-signal at point c. is now 1/10 of the signal on the line because it is further divided by two from point b. (R7Zbal). Hence 10 x R1 R2 to satisfy the balancing criteria. R12 is to set the receiver gain. ( can also be a volume control potentiometer). Note #1 These values ensure that the frequency behaviour of the transmitter is not influenced. With the ratio 1/10 the influence is 1 dB, and with ratio 1/20 its 0.5 dB. Note #2 If the R7 is made low ohmic compared with Zbal, it will load the latter and result in a bad side tone perfomannce, again if the R7 is made high ohmic compared with Zbal will result in a low signal to balance the side tone with and make the balancing difficult. Making any of the impedances unnecessary high will make the circuit sensitive to RFI. All values given here are approximate and serve as starting entities only. The final trimming of side tone network is a cut and try proposition because a part of the balance lies in the acoustical path between the microphone and earphone. internal current consumption ( about 1 mA). Care must be taken when connecting external load to pin 4 in order not to exeed the 700 A limit. Should this happen, it would result in an inoperative speech funktion. This circuit can not retrigger before the voltage level at C1 drops below 2V or the line voltage is below 1V. See fig. 10.
+Line 1
Start up circuit
Tx
PBL 38 5 82
DC supply
The circuit contains a start up device which function is to fast charge capacitor C1 when the circuit goes into hook- off condition. The fast charge circuit is a thyristor function between pins 1 and 4 that will stop conducting when the current drainat pin 4 is lower than 700 A + the
R3 2 4
R6
C1 -Line
Figure 11. Fast startup function.
3
C7 1m F
18
PBL 38582
1
Fast start - up
RECEIVE
Reference
17
Limiter
DC supply
+4
D1 D5
D2
6
3
2 C4
15
5,14,16 47nF
D3
D4
Telephone line
2
R1 6.2k C3 0.1m F TRANSMIT R14 10k C6 R6 75W >0.5W R2 62k R3 910 W
1
C1 68 m F
C2 15nF
Figure 12. Typical insulated DECT-set line interface. DIP package.
8
PBL 385 82
Ordering Information
Package Temp. Range Part No.
Plastic DIP Plastic SO20 Plastic SO20 Plastic SO16 Plastic SO16
-40 to +70C -40 to +70C -40 to +70C -40 to +70C -40 to +70C
PBL 385 82/1NS PBL 385 82/1SOS PBL 385 82/1SOT PBL 385 82/2SOS PBL 385 82/2SOT
Tape & Reel Tape & Reel
Information given in this data sheet is believed to be accurate and reliable. However no responsibility is assumed for the consequences of its use nor for any infringement of patents or other rights of third parties which may result from its use. No license is granted by implication or otherwise under any patent or patent rights of Ericsson Components. These products are sold only according to Ericsson Components' general conditions of sale, unless otherwise confirmed in writing.
Specifications subject to change without notice. IC4 (96087) B-Ue (c) Ericsson Components AB December 1999 Ordering number:
Ericsson Components AB S-164 81 Kista-Stockholm, Sweden Telephone: (08) 757 50 00
9

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