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October 1999 PBL 388 12
PBL 388 12 Voice-switch circuit for Handsfree speakerphone TAM
Description
The PBL 388 12 contains all the necessary circuitry, amplifiers, detectors, comparators and control functions to implement a high performance, voice-switched, "hands-free " function in an answering machine. The gain dynamics (attenuation between channels) is settable (25dB or 50dB) via CTR pin that also control two mute levels. A background noise detector in the transmitting channel reduces the influence of continuous noise signals. The PBL 388 12 is designed for answering machines that are either powered from the telephone line or from a mains powered dc. supply. Filtering of both the audio and control signals in both transmitter and receiver channels possible. An external loudspeaker amplifier has to be used, normally the same as used for the answering machine. All figures in this paper refer to 16-pin SO package.
Key Features
* Settable gain dynamics (25 or 50 dB). * Low power consumption, totally 1.0mA at 3.3V typical. * Background noise compensation in the transmitting channel with hold function. * Exellent noise performance. * Both channel input amplifiers have balanced inputs. * Minimum of external components needed for function. * 16-pin SO and 18-pin DIP encapsulation.
1 5
PBL 388 12
F3 Control F6
12 16
4 6 15
13 11
P
B
L
38
8
16-pin SO
+ F2 F5
2 3
- F1 +
8 7 9 10
F4 +
Ref.
P
14
B L
18-pin DIP
Figure 1. Block diagram. ( SO - package )
38 8
12
12
1
PBL 388 12
Maximum Ratings
Parameter Speech switch supply current Voltage pin 1-14 Operating temperature Storage temperature Symbol ID TAmb TStg Min -0,5 -20 -55 Max 10 Vpin 15+0.5 +70 +125 Unit mA V C C
RxDetin 11 100nF ID + 15 V + V+ GND 16
PBL 388 12
RxDetout 10 V Ref
Figure 2. Isolation and measurement of VRef. Reference figure No.2.
V+ ID + V Txout R Txout
10 F +
+ 100F/16V
15 V+ 5 Tx out
GND 16 Rxout 12 Rx Detin 11
10 F +
V Rxout R Rxout
6 Tx Detin F2 out R F2 out
10 F +
C Tx 4 F2 out
+
PBL 388 12
C Rx F5 out 13
1 F I Rxin +
10 F +
F5 out R F5 out
I Txin 4.7 F 3 +Tx in 2 -Tx in N Det 8 Tx Detout 7
0,1F
V Txin
1 F
+
CMP 9 C RxDet
Rx Detout 10
+
CTR 1
-Rx in 14
C TxDet +
V Rxin R CTR I CTR
NDet
I TxDet V
TxDet
I RxDet V
CMP
V NDet
VRxDet
V CTR
Figure 3. Test circuit. Reference figure No. 3.
2
PBL 388 12
Electrical Characteristics
f = 1 kHz, T = 25C, RCTR=0, CTxDet = 0, RTxout = , RRxout= , RF2out= , RF5out= , RTx= 0, RRx= 0, CRxDet = 0 and ID=1.0mA unless otherwise noted. Parameter Speech control section Terminal voltage, V+ Internal reference voltage, VRef Frequency response for all amplifiers Transmit gain, 20 * 10 log(VTxout /VTxin) Ref. fig. 3 2 3 3 Condition ID = 1.0mA 200 - 3400 Hz, Relative 1 kHz VCMP = VRef - 0.1 V VCMP = VRef + 0.1 V VCMP = VRef - 0.1 V RCTR=100k, VCTR=V+ VCMP = VRef + 0.1 V RCTR=100k, VCTR=V+ VCMP = VRef + 0.1 V VCMP = VRef - 0.1 V VCMP = VRef + 0.1 V RCTR=100k, VCTR=V+ VCMP = VRef - 0.1 V RCTR=100k, VCTR=V+ VTxDet < 200 mVp , CTx = 100nF VCMP = VRef - 0.1 V VCMP = VRef + 0.1 V VRxDet < 200 mVp , CTx = 100nF VCMP = VRef +0.1 V VCMP = VRef - 0.1 V VCMP = VRef - 0.1 V, CTxdet=1F VCMP = VRef + 0.1 V, CTxdet=1F -1 41.5 41.5 26.5 26.5 Min. Typ. 3.3 1.96 1 44 -6 44 19 29 -21 29 4 67.5 42.5 53 28 6.0 Hold 100 3.0 20 -3.5 21.5 -18.5 6.5 Max. Unit. V V dB dB dB dB dB dB dB dB dB dB dB dB dB dB 120 3.6 24 k k k k k k k mVp mVp dBpsof dBA mA mA A A V V mA A
Receive gain, 20 * 10 log(VRxout /VRxin)
3
Max transmit detector gain, 20 * 10 log(VTxdet /VTxin) Max receive detector gain, 20 * 10 log(VRxdet /VRxin)
3
37
3
22.5
Background noise rectifier gain, (note 1) 3 + TxIn input impedance - TxIn input impedance - RxIn input impedance TxOut ac, load impedance RxOut ac, load impedance F2Out ac, load impedance F5Out ac, load impedance Transmitter channel output swing, vTxOut Receiver channel output swing, vRxOut Transmitter output noise, vTxOut Receiver output noise, vRxOut TxDet sink current, ITxDetOut RxDet source current, IRxDetOut TxDet source current, ITxDet RxDet sink current, IRxDetOut TxDet swing relative to VRef , VTxDetOut RxDet swing relative to VRef , VRxDetOut NDet sink current (fast charge), INDet NDet source current, INDet 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3
80 2.4 16 10 10 10 10 2% distortion,RTxout=RRxout=25k 2% distortion,RTxout=RRxout=25k VCMP = VRef - 0.1 V, vTxIn = 0 V VCMP = VRef + 0.1 V, vRxIn = 0 V VTxDetIn = VRef + 0.1 V VRxIn = VRef - 0.1 V VCMP = VRef - 0.1 V VRxDetIn = VRef + 0.1 V VTxDetIn = VRef + 0.1 V VRxDetIn = VRef - 0.1 V VTxDetIn = VRef - 0.1 V VCMP = VRef - 0.1 V VTxDetIn = VRef + 0.1 V VCMP = VRef + 0.1 V
2.5 -30 (note 2) (note 2)
500 500 -75 -75 -6.0 6.0
-2.5 30
-0.7 +0.7 -4.5 5
-1.5 7
3
3
PBL 388 12
Parameter NDet leakage current (hold), INDet NDet swing relative to VRef , VNDet CMP (comparator) sensitivity, transmit (Tx) mode to receive (Rx) mode or vice versa CTR voltage for 25 dB dynamics, VCTR CTR voltage for mute, ICTR CTR voltage for disable, VCTR
Ref. fig. 3 3 3 13 3 3 3
Conditions VTxDetIn = VRef - 0.1 V, VCMP = VRef + 0.1 V, VCMP = VRef - 0.1 V, VTxDetIn = VRef + 0.1 V Tx mode = max Tx gain, Rx mode = max Rx gain VCMP = VRef 0.35 V, RCTR=100k VCMP = VRef 0.35 V
Min.
Typ. -100 -0.45 50
Max.
Unit. nA V
100
mV
V+ 0.55
V A V
Notes:
1. 20 * 10log ( VNDet = VRef = VTxDet = VTxDetO= VNDet - VRef ) VTxDet - VTxDetO
voltage at noise detector output reference voltage (about 1.9 V) see figure 2. Voltage at transmit detector output. voltage at transmit detector output at the point when the voltage at the noise detector starts moving when a signal at transmit channel input is gradually increased (threshold, typical value 30 mV)
2.
Depends on V+. Channels are tracking.
4
PBL 388 12
F2out 1
18 +Txin 17 -Txin 16 CTR 15 NC 14 GND 13 +V 12 -Rxin 11 +Rxin 10 F5out
CTR 1 -Txin 2 +Txin 3 F2out 4 Txout 5 TxDetin 6 TxDetout 7 NDet 8
16 15 14 13 12 11 10 9
GND +V -Rxin F5out Rxout RxDetin RxDetout CMP
Txout 2 TxDetin 3 TxDetout 4 N Det 5 CMP 6 RxDetout 7 Rx Detin 8 Rxout
9
16-pin SO
18-pin DIP
Figure 4. Pin configuration.
Pin Descriptions:
Refer to figure 4. (16-pin SO and 18-pin DIP package) Pin Pin SO DIP Symbol 1 2 3 4 5 6 7 16 17 18 1 2 3 4 CTR -Txin +Txin F2out Txout TxDetin TxDetout Description Control input for gain dynamics (25 or 50dB), mute and disable. Transmitter channel negative input. Input impedance 3 kohm. Transmitter channel positive input. Input impedance 100 kohm. Output of the second amplifier in the transmitter channel. Transmitter channel output. Min. ac load impedance 10 kohm. Input of the transmitter channel signal detector. Input impedance 13 kohm. Output of the transmitter channel signal detector. Goes nagative referred to the internal ref. voltage of app. 2V when a transmitter signal is present. Background noise detector output. Goes positive referred to the internal ref. voltage of app. 2V when a backgrounud noise signal is present 11 12 13 8 9 10 11 14 15 12 13 RxDetin Rxout F5out +Rxin -Rxin V+ Pin Pin SO DIP Symbol 9 6 CMP Description Comparator input.. Summing point to the different detector outputs. Output of the receiver channel signal detector. Goes positive referred to the internal ref. voltage of app. 2V when a receiver signal is present Input of the receiver channel signal detector. Input impedance 13 kohm. Receiver channel output. Min. ac load impedance 10 kohm. Output of the second amplifier in the receiver channel. Receiver channel positive input. Input impedance 140 kohm. Receiver channel negative input. Input impedance 20 kohm. Supply of the speech switching circuitry. A shunt regulator, voltage apprx. 3.3V at 1.0mA. System ground. Not connected.
10
7
RxDetout
8
5
NDet
16
14 15
GND NC
5
PBL 388 12 Functional Description Speech control section
PBL 388 12
Control F3
4 6 12 16
CTR Txout
1 5
R xout
GND
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 30,5 dB and 15.5 dB respectively, while the rest of them are of controlled gain type.The gain of F2, F3 as well as F5 and F6 is controlled by comparators. The comparator receives its information partly from the summing point of the transmitter, receiver and background noise detectors at CMP input and partly through the control input, CTR, which controls the gain dynamics (25 or 50 dB). Amplifiers F2 and F3 have the maximum gain when the transmitter channel is fully open, consequently the amplifiers F5 and F6 will have minimum gain and vice versa. See figure 5 and figure 11. The positive input on transmitter and the negative input on receiver channel has a rather high input impedance. It renders a good gain precision and noise performance when used with low signal source impedance. The differential input of the transmitter channel can be used to suppress unwanted signals in the microphone supply, see figure 7. Also see application 1.
F6
13 11
V+
15
+
F2
-Txin
+Txin 2 3
F5 F4
14
F1 +
8 7 9 10
Ref.
R xin
N Det
R5 +
TxDet
CMP
R xDet
+
C4
C3
C1
+
C2
Figure 5. Passive networks setting the speech control function.
PBL388 12
F2
Ref. 100k 100k 120k 120k I
F5
F1
2 Tx 3 V Txin 3k 3k
+
+
F4
20k 14 16 VRxin Rx
Signal Detectors and 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 an decreasing level at TxDetout and hence also at CMP input.
~
~
Figure 6. Receiver and transmitter channel input arrangement.
6
PBL 388 12
Figure 7. Transmitter channel input amplifier used to suppress ripple in the mic. supply. (CMRR). R1 = R2 3k R3 = R4 100k R5 = R6 C1 = C2
+
F2
Ref. R4 R3
R7 R6 C2
R2 2 R5 C4 Mic. C1 C3 3 R1
F1
+
16
Figure 8. Transmitter and receiver channel rectifier characteristics.
V RxDet
+600 +400 +200
V ref 2V
Vref
-200
2.5
0.5
5.0
7.5
1.0
10
1.5
V Rx in
mVp
V Tx in
-400
-600
V TxDet
Figure 9. Relationship in timing between the voltage levels at TxIn, TxDet and NDet
Txin
TxDetout
N Det
Figure 10. Transmitter and receiver channel output dynamics.
500
V Txout
(mV)
V Rxout
(mV)
500
400
400
300
300
200
200
100
100
2.4
2.6
2.8
3.0
3.2
3.4
V+ (V)
V+ (V)
2.4 2.6 2.8 3.0 3.2 3.4
7
PBL 388 12
the transmitter channel and decrease it in the receiver channel. Signal at Rxin will do vice versa. The voltages RxDetout and TxDetout control thus the gain setting in respective channel through the comparators using the CMP input as a summing point with an input current of less than 1A. The attack and decay times for the signals RxDetout and TxDetout are controlled by individual external RCnetworks. The attack time in the receiver channel is set by C2 together with C1 and either by the maximum current capability of the detector output or it with R2 added. The transmitter channel works likewise. See fig. 7. The decay time in the receiver and transmitter channels is set by C2 and C3 respectively. The resistor in the time constant is formed by an internal 200k resistor in parallel with the external resistors R3 and R4 respectively. The influence of eventual R1 and R2 can be omitted. The text above describes the case when only one channel is open at a time and there is a distinctive pause between signals at receiver and transmitter channel inputs so the circuit will have time to reach its idle state. See fig.14 A) to E). If one of the channels gets an input signal immediately after the signal has disappeared from the other channel input the effective decay time, as the CMP input sees it, will be shorter than in the first case. See fig.14 F) to G). The capacitor C4 at CMP - input sets the speed of the gain change in the transmitter and receiver channels. The capacitors C2 and C3 should be dimensioned for a charging time of 0.5 - 10mS and for a discharge time of 150 - 300 mS. The question of switching times being a highly subjective proposition, is in large dependent of the language being spoken in the system, caused by the varying sound pressure picture of the different languagues. A hysteresis effect is achieved in the switching since the level detectors sense the signals after F2 and F5 respectively (F2 and F5 are affected by the gain setting). For example: If the transmitter channel is open (maximum gain), a smaller signal at Txin is enough to keep the channel open than would benecessary to open it when the receiver channel is open. The output swing of the level detectors is matched for variations in the supply voltage. The detectors have
dB
Transmit gain = ____
Receive gain = ---------
dB
30 40 20 30
VCTR=V+ VCTR=V+
10 0
20
10 -10 0
VCTR=open VCTR=open
-20 VCMP -V REF mV
VCTR = VREF -60 -40 -20 0 20 40 60
Figure 11. Transmit and receive gain as a function of VCMP and VCTR.
Rxdet Txdet
A B E Full recieve level C CMP Full transmit level D F G
Figure 12. Timing of the transmitter and receiver channels at the CMP-input.
Mode
Vref
25 dB speech control 50 dB speech control DTMFMute Total mute
VCTR 0 1 2 3 (V)
Figure 13. Control modes as function of voltage applied to gain dynamics control input CTR; ID=1mA.
8
PBL 388 12
Transmitter channel output CTR R Txout 5 C Control P1 F3 4 +L 6 R +C C + R C 2 R Tx in 3 C Mic. C C4 + R5 C3 + C1 + C2 +Tx in + 8 N Det Tx Det 7 CMP 9 10 Rx Det C R F1 Ref. F4 14 Rx in C 15 + F2 F5 R 11 16 GND F6 13 Receiver input 1
PBL 388 12
12 Rx out C
Power amplifier input
Figure 14. Speech switching arrangement.
a logarithmic rectifier characteristic whereby gain and sensitivity is high at small signals. There is a break point in the curve at a level of 200mV from the internal reference voltage app. 2V, where the sensitivity for increasing input signals decreases with factor of 10, increasing the detectors dynamic range. See fig.10.
Background Noise Detector
The general function of the background noise detector in the transmittng channel is to create a positive signal ( in respect to the referrence) so that, when coupled to the summing point at the CMP input, will counteract the signal from the transmitter level detector representing the actual sound pressure level at the microphone. This counteracts the noise from influencing the switching characteristics. The input signal to the backround noise level detector is taken from the output of the transmitter detector , a voltage representing the envelope of the amplified microphone signal. The detector inverts and amplifies this signal 2 x (transmitting mode) and has on its output a RC network consisting of an internal resistor of 100k
and an external capacitor C4. The voltage across C4 is connected to the CMP input (summing point) via a resistor R5. The resistor R6 is important in order to keep the charging current of C4 within safe limits in regard of high charge peaks that could be audible in the system.. The extent to which the NDet output will influence the potential at CMP input is set by the gain of the detector, the maximum swing and R5. If a continuous input signal is received from the microphone ( > 10sec.) the voltage across C4 is pulled negative (relative to the reference) with a time constant set by C4 to e.g. 5 sec.. A continuous input signal is thus treated as noise. Since the output of the noise detector is going negative it thereby counteracts the signal from the transmitter detector and thus helping the receiver detector signal to maintain a set relation to the transmitter detector signal. If the transmitter input signal contains breaks like breath pauses the voltage at TxDetout decreases. If the voltage across C3 gets less than the inverted voltage across C4 divided by the detector gain a rapid charge of C4 towards reference will follow (all levels referred to the reference). If the breaks are frequent as in speech the background detector will not influence the
switching characteristic of the system. See fig. 11. There is a threshold of approx. 50mV at TxDetout to prevent the activation of background noise detection in noiseless environment. In the receiver mode some of the loudspeaker output signal will be sensed by the microphone. In order not to treat this input signal as noise, the noise detector goes into a hold state and "remembers" the level from the previous transmitting mode periode.
CTR Input
For full speech control (50dB attenuation between the channels) this input can be left unconnected. To set the function to 25dB attenuation the input has to be higher than 600mV below V+. See figure 13. To set the circuit into a mute state (results in, redeced gain in receiver channel for the DTMF confidence tone in the loudspeaker and closed transmitter channel) a voltage below Vref has to be connected to the input. By lowering the voltage at the input below 0.9V a condition will emerge where both receiver and transmitter channels are closed. See fig. 11 and 15.
9
PBL 388 12
ID=1mA +V
PBL 388 12
15
+
The circuit has a buit in shunt voltage generator. It needs a minimum 1 mA current for its function. The voltage at this current will be 3.3V. If the voltage +V is not constant care must be taken so that the ID will not exeed 10 mA.
Figure 15. Circuit supply function.
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 AB. These products are sold only according to Ericsson Components AB' general conditions of sale, unless otherwise confirmed in writing.
Specifications subject to change without notice. 1522-PBL 388 12/1 Uen Rev.A October 1999 (c) Ericsson Components AB,
Ordering Information
Package Temp. Range Part No.
Ericsson Components AB S-164 81 Kista-Stockholm, Sweden Telephone: (08) 757 50 00
Plastic SO Plastic SO Plastic DIP
-20 to 70C -20 to 70C -20 to 70C
PBL 388 12/1SO PBL 388 12/1SO:T (Tape and Reel) PBL 388 12
10

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