Philips TEA1068T, TEA1068 Datasheet

INTEGRATED CIRCUITS

DATA SH EET

TEA1068

Versatile telephone transmission
circuit with dialler interface

Product specification
Supersedes data of June 1990
File under Integrated Circuits, IC03

1996 Apr 23

Philips Semiconductors Product specification

V ersatile telephone transmission circuit

TEA1068

with dialler interface

FEATURES

• Voltage regulator with adjustable static resistance

• Provides supply for external circuitry

• Symmetrical high-impedance inputs (64 kΩ) for

dynamic, magnetic or piezoelectric microphones

• Asymmetrical high-impedance input (32 kΩ) for electret
microphone

• Dual-Tone Multi-Frequency (DTMF) signal input with
confidence tone

• Mute input for pulse or DTMF dialling

• Power down input for pulse dial or register recall

• Receiving amplifier for magnetic, dynamic or

piezoelectric earpieces

QUICK REFERENCE DATA

SYMBOL PARAMETER CONDITIONS MIN. TYP. MAX. UNIT

V
I

LN

line

line voltage I
line current

TEA1068 normal operation 10 − 140 mA
TEA1068T normal operation 10 − 100 mA

I

CC

V

CC

G

v

internal supply current power down; input LOW − 0.96 1.3 mA

supply voltage for peripherals I

voltage gain

microphone amplifier 44 − 60 dB
receiving amplifier 17 − 39 dB

∆G

v

V

exch

R

exch

T

amb

line loss compensation gain control range 5.5 5.9 6.3 dB
exchange supply voltage 24 − 60 V
exchange feeding bridge resistance range 0.4 − 1kΩ
ambient operating temperature −25 +75 °C

• Large gain setting range on microphone and earpiece
amplifiers

• Line current-dependent line loss compensation facility
for microphone and earpiece amplifiers

• Gain control adaptable to exchange supply

• DC line voltage adjustment facility.

GENERAL DESCRIPTION

The TEA1068 is a bipolar integrated circuit performing all
speech and line interface functions required in fully
electronic telephone sets. It performs electronic switching
between dialling and speech.

= 15 mA 4.2 4.45 4.7 V

line

power down; input HIGH − 55 82 µA

= 15 mA;

line

MUTE = HIGH

= 1.2 mA 2.8 3.05 − V

I

p

I

= 1.7 mA 2.5 −−V

p

ORDERING INFORMATION

TYPE

NUMBER

TEA1068 DIP18
TEA1068T SO20

NAME DESCRIPTION VERSION

plastic dual in-line package; 18 leads (300 mil) SOT102-1
plastic small outline package; 20 leads; body width 7.5 mm SOT163-1

1996 Apr 23 2

PACKAGE

Philips Semiconductors Product specification

Versatile telephone transmission circuit
with dialler interface

BLOCK DIAGRAM

11 (12)

8 (9)
7 (7)

V

CC

15 (17) 1 (1)

TEA1068

TEA1068T

handbook, full pagewidth

IR

MIC+
MIC−

LN

6 (6)
5 (5)
4 (4)

2 (2)

TEA1068

GAR
QR+
QR−

GAS1

PD

13 (15)

14 (16)

12 (14)

dB

SUPPLY AND
REFERENCE

EE

DTMF

MUTE

The figures in parentheses refer to the TEA1068T.

CIRCUIT

CURRENT

REFERENCE

16 (18) 17 (19)10 (11)

Fig.1 Block diagram.

AGC

9 (10) 18 (20)

MBH130

3 (3)

GAS2

SLPESTABAGCREGV

1996 Apr 23 3

Philips Semiconductors Product specification

Versatile telephone transmission circuit
with dialler interface

PINNING

SYMBOL

TEA1068 TEA1068T

LN 1 1 positive line terminal
GAS1 2 2 gain adjustment transmitting amplifier
GAS2 3 3 gain adjustment transmitting amplifier
QR− 4 4 inverting output receiving amplifier
QR+ 5 5 non-inverting output receiving amplifier
GAR 6 6 gain adjustment receiving amplifier
MIC− 7 7 inverting microphone input
n.c. − 8 not connected
MIC+ 8 9 non-inverting microphone input
STAB 9 10 current stabilizer
V

EE

IR 11 12 receiving amplifier input
n.c. − 13 not connected
PD 12 14 power-down input
DTMF 13 15 dual-tone multi-frequency input
MUTE 14 16 mute input
V

CC

REG 16 18 voltage regulator decoupling
AGC 17 19 automatic gain control input
SLPE 18 20 slope (DC resistance) adjustment

PIN

DESCRIPTION

10 11 negative line terminal

15 17 positive supply decoupling

TEA1068

handbook, halfpage

LN
GAS1
GAS2

QR−
QR+

GAR

MIC−

MIC+

STAB

1
2
3
4
5
6
7
8
9

TEA1068

MBH132

SLPE

18

AGC

17
16

REG
V

15

CC

MUTE

14

DTMF

13

PD

12
11

IR
V

10

EE

Fig.2 Pin configuration TEA1068.

1996 Apr 23 4

handbook, halfpage

Fig.3 Pin configuration TEA1068T.

LN
GAS1
GAS2

QR−
QR+

GAR

MIC−

n.c.

MIC+

STAB

1
2
3
4
5

TEA1068T

6
7
8
9

10

MBH131

20

SLPE
AGC

19
18

REG
V

17

CC

16

MUTE

15

DTMF
PD

14
13

n.c.
IR

12

V

11

EE

Philips Semiconductors Product specification

Versatile telephone transmission circuit
with dialler interface

FUNCTIONAL DESCRIPTION
Supplies: V

Power for the TEA1068 and its peripheral circuits is usually
obtained from the telephone line. The TEA1068 develops
its own supply at V
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 voltage (V
(R

) and the DC resistance of the telephone line (R

exch

An internal current stabilizer is set by a resistor of 3.6 kΩ
between the current stabilizer pin STAB and V
(see Fig.9).

If the line current I
required by the circuit itself (approximately 1 mA) plus the
current Ip required by the peripheral circuits connected to
VCC, then the voltage regulator diverts the excess current
via LN.

The regulated voltage on the line terminal (VLN) can be
calculated as:

VLN=V

or

VLN=V

where V
compensated reference voltage of 4.2 V and R9 is an
external resistor connected between SLPE and VEE.
The preferred value for R9 is 20 Ω. Changing the value of
R9 will also affect microphone gain, DTMF gain, gain
control characteristics, side-tone level, the maximum
output swing on LN and the DC characteristics (especially
at lower voltages).

Under normal conditions, when I
the static behaviour of the circuit is that of a 4.2 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 (see Fig.4).

The internal reference voltage can be adjusted by means
of an external resistor (RVA). This resistor, connected
between LN and REG, will decrease the internal reference
voltage; when connected between REG and SLPE, it will
increase the internal reference voltage. Current (Ip)
available from VCC for supplying peripheral circuits

, LN, SLPE, REG and STAB

CC

and regulates its voltage drop. The

CC

), the feeding bridge resistance,

exch

exceeds the current ICC+ 0.5 mA

line

ref+ISLPE

+ [(I

ref

is an internally generated temperature

ref

× R9

− ICC− 0.5 × 103) − Ip] × R9

line

>> ICC+ 0.5 mA + Ip,

SLPE

line

EE

TEA1068

depends on external components and on the line current.
Figure 10 shows this current for V
VCC> 3 V, this being the minimum supply voltage for most
CMOS circuits, including voltage drop for an enable diode.
If MUTE is LOW, the available current is further reduced
when the receiving amplifier is driven.

andbook, halfpage

).

Rp= 17.5kΩ
Leq= C3 × R9 × R

LN

L

eq

V

ref

R9
20 Ω

V

EE

p

Fig.4 Equivalent impedance circuit.

Microphone inputs MIC+ and MIC− and gain
adjustment pins GAS1 and GAS2

The TEA1068 has symmetrical microphone inputs.
Its input impedance is 64 kΩ (2 × 32 kΩ) and its voltage
gain is typically 52 dB (when R7 = 68 kΩ; see Fig.14).
Dynamic, magnetic, piezoelectric or electret (with built-in
FET source followers) microphones can be used.

The arrangements with the microphone types mentioned
are shown in Fig.11.

The gain of the microphone amplifier can be adjusted
between 44 dB and 60 dB. The gain is proportional to the
value of the external resistor R7 connected between GAS1
and GAS2. An external capacitor C6 of 100 pF between
GAS1 and SLPE is required to ensure stability. A larger
value may be chosen to obtain a first-order low-pass filter.
The cut-off frequency corresponds with the time constant
R7 × C6.

> 2.2 V and for

CC

R

p

REG

C3

4.7 µF

MBA454

R1

V

CC

C1
100 µF

1996 Apr 23 5

Philips Semiconductors Product specification

Versatile telephone transmission circuit
with dialler interface

Mute input (MUTE)

A HIGH level at MUTE enables the DTMF input and
inhibits the microphone and the receiving amplifier inputs.

A LOW level or an open circuit has the reverse effect.
MUTE switching causes only negligible clicks at the
earpiece outputs and on the line.

Dual-Tone Multi Frequency input (DTMF)

When the DTMF input is enabled, dialling tones may be
sent onto the line. The voltage gain from DTMF to LN is
typically 25.5 dB (when R7 = 68 kΩ) and varies with R7 in
the same way as the gain of the microphone amplifier.
The signalling tones can be heard in the telephone
earpiece at a low level (confidence tone).

Receiving amplifier: IR, QR+, QR− and GAR

The receiving amplifier has one input IR and two
complementary outputs, a non-inverting output QR+ and
an inverting output QR−. These outputs may be used for
single-ended or for differential drive depending on the
sensitivity and type of earpiece used (see Fig.12). Gain
from IR to QR+ is typically 25 dB (when R4 = 100 kΩ).
This is sufficient for low-impedance magnetic or dynamic
microphones, which are suited for single-ended drive.
By using both outputs (differential drive), the gain is
increased by 6 dB. This feature can be used when the
earpiece impedance exceeds 450 Ω, (high-impedance
dynamic or piezoelectric types).

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 ratio of peak
to RMS value is higher.

The receiving amplifier gain can be adjusted between
17 dB and 33 dB with single-ended drive and between
26 dB and 39 dB with differential drive to suit the sensitivity
of the transducer used. The gain is set by the external
resistor R4 connected between GAR and QR+. Overall
receive gain between LN and QR+ is calculated by
subtracting the anti-side-tone network attenuation (32 dB)
from the amplifier gain. Two external capacitors,
C4 = 100 pF and C7 = 10 × C4 = 1 nF, are necessary to
ensure stability. A larger value of C4 may be chosen to
obtain a first-order, low-pass filter. The ‘cut-off’ frequency
corresponds with the time constant R4 × C4.

TEA1068

Automatic Gain Control input AGC

Automatic line loss compensation is achieved by
connecting a resistor R6 between AGC and V
automatic gain control varies the microphone amplifier
gain and the receiving amplifier gain in accordance with
the DC line current.

The control range is 5.9 dB. This corresponds to a line
length of 5 km for a 0.5 mm diameter copper twisted-pair
cable with a DC resistance of 176 Ω/km and an average
attenuation 1.2 dB/km.

Resistor R6 should be chosen in accordance with the
exchange supply voltage and its feeding bridge resistance
(see Fig.13 and Table 1). Different values of R6 give the
same ratio of line currents for start and end of the control
range. If automatic line loss compensation is not required,
AGC may be left open. The amplifiers then all give their
maximum gain as specified.

Power-Down input (PD)

During pulse dialling or register recall (timed loop break),
the telephone line is interrupted. During these
interruptions, the telephone line provides no power for the
transmission circuit or circuits supplied by V
held on C1 will bridge these gaps. This bridging is made
easier by a HIGH level on the PD input, which reduces the
typical supply current from 1 mA to 55 µA and switches off
the voltage regulator, thus preventing discharge through
LN. When PD is HIGH, the capacitor at REG is
disconnected with the effect that the voltage stabilizer will
have no switch-on delay after line interruptions. This
minimizes the contribution of the IC to the current
waveform during pulse dialling or register recall. When this
facility is not required, PD may be left open-circuit.

Side-tone suppression

Suppression of the transmitted signal in the earpiece is
obtained by the anti-side-tone network consisting of
R1//Z

, R2, R3 and Z

line

(see Fig.14). Maximum

bal

compensation is obtained when the following conditions
are fulfilled:

R9 R2× R1 R3 R8//Z

Z

balZbal

R8+()⁄ Z

[]+()=

bal

lineZline

R1+()⁄=[]

. This

EE

. The charge

CC

(1)
(2)

1996 Apr 23 6

Philips Semiconductors Product specification

Versatile telephone transmission circuit
with dialler interface

If fixed values are chosen for R1, R2, R3 and R9, then
condition (1) will always be fulfilled, provided that
R8//Z
suppression, condition (2) has to be fulfilled, resulting in:

Z

bal

k = (R8/R1).
Scale factor k (dependent on the value of R8) must be

chosen to meet the following criteria:

1. Compatibility with a standard capacitor from the E6 or

2. Z

3. Z

In practice, Z
cable type; consequently, an average value has to be

 << R3. To obtain optimum side-tone

bal

= (R8/R1) Z

E12 range for Z

//R8<< R3 to fulfil condition (1) and thus

bal

line

= k × Z

bal

, where k is a scale factor:

line

ensuring correct anti-side-tone bridge operation

+R8>> R9 to avoid influencing the transmitter

bal

gain.

varies greatly with the line length and

line

TEA1068

chosen for Z
long lines.

Example: the balanced line impedance (Z
optimum suppression is preset can be calculated by:

Assume Z
5 km line of 0.5 mm diameter, copper, twisted-pair cable
matched to 600 Ω (176 Ω/km; 38 nF/km). When k = 0.64,
then R8 = 390 Ω; Z

The anti-side-tone network for the TEA1060 family shown
in Fig.5 attenuates the signal received from the line by
32 dB before it enters the receiving amplifier.
The attenuation is almost constant over the whole audio
frequency range.

Figure 6 shows a conventional Wheatstone bridge
anti-side-tone circuit that can be used as an alternative.
Both bridge types can be used with either resistive or
complex set impedances.

, thus giving an optimum setting for short or

bal

) at which the

bal

= 210 Ω + (1265 Ω/140 nF), representing a

line

= 130 Ω + (820 Ω//220 nF).

bal

handbook, full pagewidth

LN

Z

line

V

R1

EE

R9

SLPE

R2

i

m

R3

R8

IR

R

t

Z

bal

MSA500

Fig.5 Equivalent circuit of TEA1060 family anti-side-tone bridge.

1996 Apr 23 7

Philips Semiconductors Product specification

Versatile telephone transmission circuit
with dialler interface

book, full pagewidth

Z

line

V

R1

EE

R9

Fig.6 Equivalent circuit of an anti-side-tone network in a Wheatstone bridge configuration.

LN

SLPE

i

m

R8

TEA1068

Z

bal

IR

R

t

R

A

MSA501

LIMITING VALUES

In accordance with the Absolute Maximum Rating System (IEC 134).

SYMBOL PARAMETER CONDITIONS MIN. MAX. UNIT

V
V

LN
LN(R)

positive continuous line voltage − 12 V
repetitive line voltage during switch-on or

− 13.2 V

line interruption

V

LN(RM)

I

line

V

n

P

tot

repetitive peak line voltage for a 1 ms pulse
per 5 s

R9 = 20 Ω;
R10 = 13 Ω; (Fig.15)

− 28 V

line current R9= 20 Ω; note 1 − 140 mA
voltage on any other pin VEE− 0.7 VCC+ 0.7 V
total power dissipation R9= 20 Ω; note 2

TEA1068 − 769 mW
TEA1068T − 555 mW

T

stg

T

amb

T

j

IC storage temperature −40 +125 °C
operating ambient temperature −25 +75 °C
junction temperature − 125 °C

Notes

1. Mostly dependent on the maximum required T

and on the voltage between LN and SLPE. See Figs 7 and 8 to

amb

determine the current as a function of the required voltage and the temperature.

2. Calculated for the maximum ambient temperature specified T

= 75 °C and a maximum junction temperature of

amb

125 °C.

1996 Apr 23 8