TP5700A [NSC]
Telephone Speech Circuit; 电话语音电路
| 型号： | TP5700A |
| 厂家： | 
National Semiconductor |
| 描述： | Telephone Speech Circuit |
| 文件： | 总8页 (文件大小：182K) |
| 中文： | 中文翻译 | 下载： | 下载PDF数据表文档文件 |
December 1989
TP5700A
Telephone Speech Circuit
General Description
Features
Y
5 mA–120 mA loop operation
The TP5700A is a linear bipolar device which includes all
the functions required to build the speech circuit of a tele-
phone. It replaces the hybrid transformer, compensation cir-
cuit and sidetone network used in traditional designs. When
used with an electret microphone (with integral FET buffer)
and dynamic receiver, superior audio linearity, distortion and
noise performance are obtained. Loop attenuation compen-
sation is also included.
Y
Voltage swing down to 1.0V
Y
Electret microphone amplifier
Y
Receive amplifier with push-pull outputs
Y
Automatic gain compensation for loop length
Sidetone impedance independent of input impedance
DTMF interface with muting
Y
Y
Y
Y
Y
Voltage regulator outputs for DTMF generator etc.
Works in parallel with a standard phone on 20 mA loop
Available in small outline surface mount package
The low voltage design enables the circuit to work over a
wide range of operating conditions, including long loops, ex-
tension telephones and subscriber carrier applications.
Operating power is derived from the telephone line.
Simplified Block Diagram
TL/H/5201–1
C
1995 National Semiconductor Corporation
TL/H/5201
RRD-B30M115/Printed in U. S. A.
Absolute Maximum Ratings
If Military/Aerospace specified devices are required,
please contact the National Semiconductor Sales
Office/Distributors for availability and specifications.
b
a
25 C to 70 C
Operating Temperature, T
§
§
1W
A
Power Dissipation (Note 3)
b
a
65 C to 150 C
Storage Temperature, T
S
§
§
Va with Respect to Vb
20V
Junction Temperature
150 C
§
b
Va
0.3V to V
a
b
0.3V
Voltage at Any Other Pin
Lead Temperature (Soldering, 10 seconds)
300 C
§
DC Electrical Characteristics
Unless otherwise specified, all tests based on the test circuits shown in Figure 1, all limits printed in bold characters are
e
a
0 C to 60 C by correlation with 100% testing at T
with other production tests, and/or product design and characterization.
e
guaranteed at T
25 C. All other limits are assured by by correlation
§
§
§
A
A
Symbol
Parameter
Conditions
Min
Typ
Max
Units
e
e
e
e
e
I
5 mA
2.8
V
V
V
V
V
LOOP
V
Tip-Ring Voltage including
nominal 1.4V polarity guard
(SeeFigure 1)
20 mA
50 mA
80 mA
120 mA
4.5
T-R
7
10.5
15
V
I
Minimum Instantaneous
Voltage Swing
Va to Vb
1.0
V
e
I
5mA
LOOP
TRANSMIT AMPLIFIER
Input Resistance
R
XIN
From Pin 7 to Vb
15
30
35
50
kX
b
e
e
G
XA
Gain at 1 kHz
R
I
0X to V
AGC
e
A
20 mA, T
25 C only
§
33
37
dB
dB
LOOP
g
b
G
G
Gain Variation v. T
1
6
XT
XI
X
A
e
Gain Variation v. I
Transmit Noise
I
20 to 100 mA
dB
LOOP
LOOP
e
N
MIC IN
0V
12
18
dBrnC
1
t
LOOP
S/D
Signal/Total Harmonic
Distortion
I
20 mA
X
e
V
800 mVrms
2
10
%
L
t
b
G
XM
Gain Change when MUTED
MUTE IN
V
MON
55
dB
DTMF AMPLIFIER
Input Resistance
R
From Pin 8 to Vb
10
20
55
kX
DIN
b
e
e
G
XD
Gain at 1 kHz
R
I
0X to V
AGC
e
e
20 mA, T
25 C only
§
3.5
5.5
3
7.5
10
dB
%
LOOP
A
e
1.06 Vrms, T
S/D
XD
Signal/Total
I
20 mA
LOOP
e
Harmonic Distortion
V
25 C only
§
L
A
g
b
G
G
Gain Variation v. T
1
6
dB
dB
XDT
A
e
20 to 100 mA
Gain Variation v. I
I
XDI
LOOP
LOOP
MUTE INPUT
e
I
Input Current
Pin 9
1.5V
40
mA
V
MIN
V
MUTE OFF Input Voltage
MUTE ON Input Voltage
0.5
MOFF
MON
V
1.5
V
2
DC Electrical Characteristics (Continued)
Unless otherwise specified, all tests based on the test circuits shown in Figure 1, all limits printed in bold characters are
e
a
0 C to 60 C by correlation with 100% testing at T
with other production tests, and/or product design and characterization.
e
guaranteed at T
25 C. All other limits are assured by by correlation
§
§
§
A
A
Symbol
Parameter
Conditions
Min
Typ
Max
Units
RECEIVE AMPLIFIER
R
Input Resistance
Gain at 1 kHz
From Pin 12 to Vb
20
35
55
kX
RIN
s
25 C only
e
e
G
R
I
0X, MUTE IN
V
RA
AGC
MOFF
e
b
b
b
2.5
20 mA, T
5.5
4
dB
dB
§
LOOP
A
g
G
G
G
Gain Variation v. T
0.5
RT
RI
A
e
b
Gain Variation v. I
I
20 to 100 mA
6
dB
LOOP
LOOP
t
b
b
b
Gain Change when MUTED
Receive Noise
MUTE IN
V
MON
15
20
23
10
10
dB
RM
R
e
N
V
0V
0
dBrnC
%
RCVIN
e
R
S/D
Signal/Total Harmonic
Distortion
V
200 mVrms
t
2
R
I
I
20 mA
LOOP
t
V
V
C
Output Clipping Level
Output Offset Voltage
20 mA
1
Vp-p
mV
R
LOOP
g
100
ROS
SIDETONE CHARACTERISTICS
s
s
100 mA, (Note 2)
STC
Sidetone Cancellation at 1kHz
20 mA
I
11
15
dB
LOOP
VOLTAGE REGULATOR OUTPUTS
t
20 mA
V
REG1
Output Voltage, Pin 10
I
LOOP
s
MUTE IN
MUTE IN
V
MOFF
V
MON
2
3
V
V
t
3.2
s
t
I
Maximum Output Current,
Pin 10
MUTE IN
MUTE IN
V
MOFF
V
MON
200
2.7
mA
mA
REG1
t
t
V
Output Voltage, Pin 11
I
20 mA
20 mA
1.1
1.2
V
REG2
LOOP
LOOP
I
Maximum Output Current, Pin 11
I
300
500
mA
REG2
TL/H/5201–3
TL/H/5201–2
1b. Test Circuit for Receive
1a. Test Circuit for Transmit and Sidetone
FIGURE 1. Test Circuits for Electrical Characteristics
Note 1. Adjust V
to set specified I
current.
LOOP
DC
e
e
100 mVrms; measure V
Note 2. To measure Sidetone Cancellation, set oscillator in Fig. 1a for V
100 mVrms; measure V . Then in Fig. 1b set oscillator
S
.
R
L
e
STC 20log V /V
.
S
R
Note 3. For operation above 25 C, the device must be derated based on a 150 C maximum junction temperature and a thermal resistance of 70 C/W junction to
§
§
§
ambiant.
MICROPHONE AMPLIFIER
Functional Description
A single-ended input amplifier on the TP5700A enables a
low cost electret microphone to be used. This provides su-
perior distortion, linearity and noise performance compared
to a traditional carbon microphone. The electret should be
capacitively coupled to the amplifier input. The acoustic
sensitivity of the microphone is intended to be in the range
The TP5700A Telephone Speech Circuits are powered from
the telephone Tip and Ring terminals via a full-wave rectifier
bridge to protect against loop polarity reversals. The devic-
es provide the following functions:
LINE REGULATOR
b
b
of 60 to 70 dBV/mBar.
A DC regulator sinks current from the loop in order to main-
tain a DC slope resistance similar to that of a standard phone.
Loss can be inserted if required by adding a resistive poten-
tiometer either at MIC IN or the connection between the
1
pre-amp output and driver stage input. The driver stage pro-
R
DC
provides an adjustment for the slope resistance.
3
DTMF AMPLIFIER
Functional Description (Continued)
vides automatic gain compensation to reduce the gain as
An additional transmit amplifier is included to enable the
open-emitter output of a conventional DTMF generator to
be connected to the line via the transmit output stage. This
path includes the transmit AGC section. When the MUTE
input is pulled high, the DTMF input is enabled and the MIC
input disabled. When MUTE IN is open-circuit or pulled to
Vb the DTMF input is switched off and the MIC input is
enabled.
loop length decreases. The AGC range can be adjusted by
to limit the maximum loss on a short loop
means of R
AGC
from 0 to 6 dB.
RECEIVE AMPLIFIER
This buffer amplifier provides the necessary gain or loss for
the receive signal. RCV IN should be AC coupled to SIDE-
TONE (pin 4). Automatic gain control is built into the amplifi-
er to reduce the gain as loop length decreases. The AGC
range is adjusted in common with the transmit AGC range
with a range of adjustment for maximum loss from 0 to 6 dB.
Push-pull complementary outputs provide balanced direct
drive to a dynamic transducer, which may have an imped-
ance as low as 100X. The effective receive gain can be
reduced by adding a resistor in series with the transducer.
The receive gain is automatically reduced by 20 dB when
the MUTE input is pulled high.
VOLTAGE REGULATOR OUTPUTS
A precision band-gap voltage reference controls a regulator
to provide bias for internal circuits. Two auxiliary outputs are
also available. V
REG1
is provided specifically for powering a
low voltage pulse dialer or DTMF generator. In order to pro-
tect this output in low voltage situations where the instanta-
neous voltage across the Speech Circuit may swing below
the V
output voltage, an internal switch controls the
REG1
maximum available output current. In speech mode, MUTE
IN is low, V output will track approximately (/2 the Tip-
REG1
SIDETONE CIRCUIT
Ring voltage and the available output current is limited to
200 mA. This is adequate to power a DTMF generator in
standby mode. When MUTE IN is pulled high to switch the
The level of Sidetone cancellation may be adjusted by con-
necting an external balance impedance to SIDETONE (pin
4) and coupling this point to Va. For good sidetone cancel-
lation the balance impedance should be approximately 10
times the subscriber line input impedance. Some typical
component values to match a precise 600X termination for
test purposes are shown in Figure 2. Use the component
values shown in the Applications Section for better results
over a wide range of telephone line impedances.
Speech Circuit to the DTMF dialing mode,
V
REG1
is
switched to a 3V regulated output and up to 2 mA may be
drawn from it to power the active DTMF generator.
A 1.2V regulated output is also provided at V
REG2
to power
a low voltage 2-wire electret microphone such as the Primo
EM80-PMI .
2
TL/H/5201–4
* See Figure 3
Note: Z circuit shown is for test purposes with a resistive line termination. See Applications Information for suggested component values for normal reactive line
BAL
applications.
FIGURE 2. TP5700A Telephone Speech Circuits
4
Connection Diagram
Dual-In-Line Package
TL/H/5201–5
Top View
Order Number TP5700AM or TP5700AN
See NS Package M16B or N16A
Pin Descriptions
Pins 1, 2 RCV0a and RCV0
b
Pin 12 RCV IN
The push-pull complementary outputs of the receive amplifi-
er. Dynamic transducers with a minimum impedance of 100
X can be directly driven by these outputs.
The receive AGC amplifier input.
Pin 13 Va
This is the positive supply input to the device and should be
connected to the positive output of the polarity guard. The
current through this pin is modulated by the transmit signal.
Pin 3 Vb
This is the negative supply input to the device and should be
connected to the negative output of the polarity guard. All
other voltages on the device are referred to this pin.
Pin 14 R
DC
An external 1W resistor is required from this pin to Vb to
control the DC input impedance of the circuit. The nominal
value is 56X for low voltage operation. Values up to 82X
may be used to increase the available transmit output volt-
age swing at the expense of low voltage operation.
Pin 4 S/T
This is the output of the Sidetone cancellation signal, which
requires a balance impedance of approximately 10 times
the subscriber’s line impedance to be connected from this
pin to Va (pin 13).
Pin 15 V
BIAS
This internal voltage bias line must be connected to Va via
Pin 5 XDI
The input to the line output driver amplifier. Transmit AGC is
applied in this stage.
an external resistor, R , and decoupled to Vb with a 22 mF
o
capacitor. R dominates the AC input impedance of the cir-
o
cuit and should be 620X for a 600X input impedance or
910X for a 900X input impedance.
Pin 6 XPO
This is the transmit pre-amp output which is normally capac-
itively coupled to pin 5.
Pin 16 R
AGC
The range of transmit and receive gain variations between
short and long loops may be adjusted by connecting a resis-
tor from this pin to Vb (pin 3). Figure 3 shows the relation-
ship between the resistor value and the AGC range. This pin
may be left open-circuit to defeat AGC action.
Pin 7 MIC IN
1
This is the inverting input to the transmit pre-amplifier and is
intended to be capacitively coupled to an FET-buffered
electret microphone.
Pin 8 DTMF IN
The DTMF input which has an internal resistor to Vb to
provide the emitter load resistor for a CMOS DTMF genera-
tor. This input is only active when MUTE IN (pin 9) is pulled
high.
Pin 9 MUTE IN
The MUTE Input, which must be pulled at least 1.5V higher
than Vb to mute MIC IN and enable DTMF IN.
Pin 10 V
REG1
The regulated output for biasing a pulse dialer or DTMF
b
generator. A 4.7 mF decoupling capacitor to V should be
fitted if this output is used.
Pin 11 V
REG2
TL/H/5201–7
A 1.2V regulated output suitable for powering a low-voltage
electret microphone. A 1mF decoupling capacitor to Vb
should be fitted if this output is used.
FIGURE 3
5
Applications Information
The TP5700A and TP5700 are flexible circuits designed
with several user adjustments to enable the performance to
be optimized for different applications. The choice of trans-
ducer types and the cavities in which they are mounted will
also greatly influence the acoustic performance of the tele-
phone. Some of the consequences of circuit adjustments
are as follows:
erating voltage ranges. There are four methods of powering
the microphone.
1. The 1.2V V
output provides the lowest voltage meth-
must be
REG2
od for microphones rated down to 1V. V
REG2
decoupled with a 1 mF capacitor to ground. (See Figure
5.)
2. If V
REG1
is not required for DTMF generator operation, it
may be used to provide up to 200 mA for microphone
power.
R
ADJUSTMENT
DC
56X is the recommended value for R
if it is required to
DC
3. V
BIAS
(pin 15) may be used as a decoupled, but unregu-
meet a maximum Tip-Ring voltage of 4.5V on a 20 mA loop
(assuming no more than 1.4V is dropped across the polarity
lated, supply for electrets requiring a higher operating
voltage than V or V . The additional current
guard). If a higher Tip-Ring voltage is acceptable, R
DC
may
REG1 REG2
drawn through R will, however, raise the minimum oper-
o
be increased, which will provide a small increase in the
available transmit output voltage swing before clipping oc-
ating voltage of the Speech Circuit. If this method is used
the decoupling capacitor must be increased to at least
100 mF to maintain good low frequency return loss. (See
Figure 4.)
curs. R
should be less than 82X to avoid exceeding the
DC
maximum rated voltage on a short loop.
R
ADJUSTMENT
AGC
The available AGC range is more than adequate to compen-
sate for the loss of most loops. R should be chosen
4. An electret type with a good power supply rejection ratio
can be powered from Va, or a regulated and decoupled
supply dropped from Va
.
AGC
only to partly compensate for the anticipated maximum loop
loss, as over-compensation may tend to exaggerate the var-
iations of sidetone with loop length.
TONE DIALING TELEPHONE
Figure 4 shows the TP5700 directly interfacing to a low volt-
age DTMF generator. V
supplies the necessary 2V
REG1
minimum bias to enable the low voltage tone dialer to sense
key closures and pull its MUTE output high. V then
SIDETONE ADJUSTMENT
The component values used for Z
BAL
should be selected to
REG1
provide a clear sidetone sound without excessive ‘‘hollow-
ness.’’ The capacitor value and ratio of the two resistors will
fix the pole location. To avoid reducing the low voltage per-
formance of the circuit the sum of the two resistors should
not exceed 10 kX.
switches to a 3V regulated output to sustain the Tone Dialer
during tone generation. The TP5700A DTMF input incorpo-
rates the necessary load resistor to Vb and provides gain
plus AGC action to compensate for loop length. A muted
tone level is heard in the receiver. For DTMF generators
with a higher output level, a resistive potentiometer should
POWERING ELECTRET MICROPHONES
Electret microphones with integral FET buffers are available
in both two-wire and three-wire versions and a range of op-
TL/H/5201–8
FIGURE 4. Typical Tone Dialing Telephone
6
Applications Information (Continued)
be added to reduce the level at the speech circuit DTMF
Input. For application requiring higher DTMF level, the signal
swing across the device can be raised by using 620X in
V
is used in its non-regulated mode and its output volt-
REG1
age may fall to 2V on a 20 mA loop. A 100 mF decoupling
capacitor is required to hold up the pulse dialer supply volt-
age during dialing. This capacitor will take about one second
to charge up when the telephone is first connected to the
line, but thereafter the 20 MX resistor required to retain the
last-number dialed memory will keep this capacitor charged.
Partial muting is obtained by directly connecting the N-chan-
nel open-drain MUTE output of the pulse dialer to the RCV
IN pin on the Speech Circuit.
series with 270X for R . The 270X has to be bypassed by a
O
10 mf capacitor in order to maintain same AC off hook im-
pedance.
PULSE DIALING TELEPHONE
The TP5700A can reduce the number of components re-
quired to build a pulse dialing telephone, as shown in Figure
5. The usual current source can be eliminated by using the
A fully muted pulse dialer design requires the use of a shunt-
mode dialer.
V
output to power a low-voltage (1.7V) series mode
REG1
pulse dialer via a blocking diode. A low forward-voltage drop
diode such as Schottky type is necessary because
a
TL/H/5201–9
*Low voltage drop diode (e.g. Schottky)
²
Low leakage type
Ý
Indicates National Semiconductor discrete transistor process number
FIGURE 5. Typical Pulse Dialing Telephone
7
Ý
Lit. 113984
Physical Dimensions inches (millimeters)
Order Number TP5700AM
NS Package Number M16B
Molded Dual-in-Line Package (N)
Order Number TP5700AN
NS Package Number N16A
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to the user.
2. A critical component is any component of a life
support device or system whose failure to perform can
be reasonably expected to cause the failure of the life
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effectiveness.
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