Datasheet UTCMC34018 Datasheet (UTC)

UTC MC34018 LINEAR INT E G R A TED CIRCUIT

VOICE SWITCHED
SPEAKER-PHONE CIRCUIT

DESCRIPTION

The UTC MC34018 speaker-phone integrated circuit
incorporates the necessary functions to produce a high
quality hands-free speaker-phone system. The applications
include household and office speaker-phones, intercom
systems, hand free kit for mobile phones, and others.

FEATURES

*All necessary level detection and attenuation controls for a
hand-free telephone included.
*Background noise level monitoring with long time constant.
*Background sound level compensation for transmit and
receive levels as well as the background level.
*Wide operating dynamic range through signal compression.
*On-chip voltage regulators illuminate external regulators for
lining operation.
*Power audio amplifier for typical 100mW output (into 25
ohms)with peak limiting for speaker to minimize distortion.
*Chip Select pin for active/stand by operation.
*Volume control function for external volume control.
*Standard 28-pin plastic DIP and SOP package.

ABSOLUTE MAXIMUM RATINGS

PARAMETER VALUE UNIT

V+ terminal Voltage (pin 16) +12,-1.0 V

CS

(pin 18)
Speaker amplifier Ground(pin 14) +3.0,-1.0 V
VLC(pin 24) +VCC,-1.0 V
Storage temperature -65 ~ +150

(Ta=25°C,Voltages referred to pin 22)

RECOMMENDED OPERATION CONDITIONS

PARAMETER VALUE UNIT

V+ Terminal Voltage (pin 16) +6.0 to +11 V

CS

(pin 18)
Icc(pin 20) 0 to 3.0 mA
VLC(pin 24) 0.55VB to VB V
Receive Signal(pin 27) 0 to 250 mVrms
Microphone Signal(pin 9) 0 to 5.0 mVrms
Speaker Amplifier Ground (pin 14) -10 to +10 mVdc
Ambient Temperature -20 to +60

SOP-28

DIP-28

+12,-1.0 V

°C

0 to +11 V

°C

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UTC MC34018 LINEAR INT E G R A TED CIRCUIT

BLOCK DIAGRAM

MIC

MIC AMP

TRANSMIT
CHANNEL

TRANSMIT

ATTENUATOR

TRANSMIT LEVEL

DETECTOR

TRANSMIT

OUTPUT

TRANSMIT/

RECEIVE

COMPARATOR

REGULATOR

RECEIVE LEVEL

DETECTOR

VCC

ENABLE INPUT

SIDE

TONE

DC INPUT

SIDE TONE
NETWORK

RECEIVE INPUT

TELEPHONE

LINE

SPEAKER

RECEIVE

CHANNEL

PEAK LIMITER

SIGNAL/NOISE

DETECTOR

SPEAKER
AMP

ATTENUATOR

CONTROL

ATTENUATOR

RECEIVE VOLUME CONTROL

RECEIVE

PIN CONFIGURATIONS

PIN NAME DESCRIPTION

1 RR A resistor to ground provides a reference current for the transmit and receive attenuators
2 RTX A resistor to ground determines the nominal gain of the transmit attenuator ,the transmit channel gain

3 TXI Input to the transmit attenuator. Input resistance is nominally 5.0k ohms.
4 TXO Output of the transmit attenuator. The TXO output signal drivers the input of transmit level detcetor,

5 TLI Input of the transmit level detector. An external resistor ac coupled to The TLI pin sets the detection

6 TLO Output of the transmit level detector. The external resistor and capacitor set the time the comparator

7 RLI Input of the receive level detector. An external resistor ac coupled to The RLI pin sets the detection

8 RLO Output of the receive level detector. The external resistor and capacitor set the time the comparator

9 MCI Microphone amplifier input. Input impedance is nominally 10k ohms and the dc bias voltage is

10 MCO Microphone amplifier output. The MIC amp gain is internally set at 34dB(50V/V).
11 CP1 A parallel resistor and capacitor connected between this pin and VCC holds a voltage corresponding

12 CP2 A capacitor at this pin peak detects the speech signals for comparison with the background noise

13 XDI Input to the transmit detector system. The microphone amplifier output is ac coupled to the XDI pin

is inversely proportional to RTX resistance.

as well as the external circuit which drivers the telephone line.

level. Decreasing this resistor increases the sensitivity to transmit channel signals.

will hold the system in the transmit mode after speech ceases.

level. Decreasing this resistor increases the sensitivity to receive channel signals.

will hold the system in the receive mode after speech ceases.

approximately equal to VB

to the background noise level. The transmit detector compares the CP1 voltage with the speech
signal from CP2.

level held at CP1.

through an external resistor.

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(continued)

PIN NAME DESCRIPTION

14 SKG High current ground pin for the speaker amplifier output stage. The SKG voltage should be within

15 SKO Speaker amplifier output. The SKO pin will source and sink up to 100mA when ac coupled to the

16 V+ Input DC supply voltage. V+ can be powered from Tip and Ring if an ac decoupling inductor is used

17 AGC A capacitor from this pin to VB stabilizes the speaker amplifier gain control loop, and additionally

18

19 SKI Input to the speaker amplifier. Input impedance is nominally 20k ohms.
20 VCC A 5.4V regulated output which powers all circuits except the speaker amplifier output stage. VCC can

21 VB An output voltage equal to approximately VCC/2 which series as an analog ground for the

22 GND Ground pin for the IC(except the speaker amplifier)
23 XDC Transmit detector output. A resistor and capacitor at his pin hold the system in the transmit mode

24 VLC Volume control input>connecting this pin to the slider of a variable resistor provides receive mode

25 ACF Attenuator control filter. A capacitor connected to this pin reduces noise transient as the attenuator

26 RXO Output of the receive attenuator. Normally this pin is ac coupled to the input of the speaker amplifier.
27 RXI Input of the receive attenuator. Input impedance is nominally is 5.0k ohms.
28 RRX A resistor to ground determines the nominal gain of the receive attenuator. The receive channel gain

ELECTRICAL CHARACTERISTICS(referred to fig. 1)

SUPPLY VOLTAGES
V+ Supply Current
V+=11V,Pin 18=0.7V
V+=11V,Pin 18=1.6V
VCC Voltage(V+=7.5V)
Line
Regulation(6.5V<V+<11V)
Output Resistance(I
Dropout Voltage(V+=5.0V)
VB Voltage(V+=7.5V)
Output Resistance(I

10mV of the ground voltage at pin 22.

speaker. The speaker amplifier gain is internally set at 34dB(50V/V).

to prevent loading ac line signals. The required V+ voltage is 6.0V to 11V(7.5V nominal ) at 7.0mA.

controls the attack and decay time of this circuit. The gain control loop limits the speaker amplifier
input to prevent clipping at SKO. The internal resistance at AGC pin is nominally 110k ohms.

CS

Digital chip select input. When at a logic "0" (<0.7V) the VCC regulator is enabled. When at a logic
"1" (>1.6V),the chip is in the standby mode drawing 0.5mA.An open
impedance is nominally 140k ohms. The input voltage should not exceed 11V.

be used to power external circuitry such as a microprocessor(3.0mA max.) A filter capacitor is
required. The UTC MC34018 can be powered by a separate regulated supply by connecting V+ and
VCC to a voltage between 4.5V and 6.5V while maintaining

speakerphone system. Up to 1.5mA of external load current may be sourced from VB. Output
impedance is 250 ohms. A filter capacitor is required.

during pauses between words or phrases. When the XDC pin voltage decays to ground, the
attenuators switch from the transmit mode to idle mode. The internal resistor at XDC is nominally

2.6k ohms(see fig.1).

volume control. The VLC pin voltage should be less than or equal to VB.

control switches level of attenuation.

is directly proportional to the RRX resistance.

CS

CS

at a logic "1".

pin is a logic "0".Input

PARAMETER SYMBOL MIN TYP MAX UNIT

V+

CC=3mA)

B=1.7mA)

I

Vcc

∆Vcc

Ro

Vcc

Vccsat

Vb

Rovb

LN

4.9

2.5

9.0

800

5.4
65

6.0
80

2.9

250

5.9

150

20

300

3.3

mA

µA
Vdc
mV

ohms

mV

Vdc

ohms

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(continued)

PARAMETER SYMBOL MIN TYP MAX UNIT

ATTENUATORS
Receive Attenuator Gain(1.0kHz)
Rx Mode, Pin 24= VB, Pin 27 =
250Mvrms
Range (Rx to Tx Modes)
Idle Mode, Pin 27= 250mVrms
RXO Voltage (Rx Mode) VRXO 1.8 2.3 3.2 mV
Delta RXO Voltage (Switch from Rx
to Tx Mode)
RXO Sink Current (Rx mode) IRXOL 75
RXO Source Current (Rx mode) IROXH 1.0 3.0 mA
RXI Input Resistance RRXI 3.5 5.0 8.0
Volume Control Range (Rx
Attenuator Gain, Rx Mode,

0.6VB<Pin 24<VB
ATTENUATORS
Transmit Attenuator Gain (1.0kHz)
Tx Mode, Pin 3 = 250mVrms
Range, (Tx to Rx Mode)
Idle Mode, Pin 3 = 250Mvrms
TXO Voltage (Tx mode) VTXO 1.8 2.3 3.2 Vdc
Delta TXO Voltage (switch from Tc
to Rx Mode)
TXO Sink Current (Tx mode) ITXOL 75
TXO Source Current (Tx mode) ITXOH 1.0 3.0 mA
TXO Input Resistance RTXI 3.5 5.0 8.0
ACF Voltage (VCC-Pin 25 Voltage)
Rx Mode
Tx Mode
Idle Mode

SPEAKER AMPLIFIER
Speaker Amp Gain (pin 19 =
20mVrms)
SKI Input Resistance RSKI 15 22 37
SKO Voltage ( Pin 19 =Cap couple
to GND)
SKO High Voltage ( Pin 19 = 0.1V,

-100mA Load at Pin 15)
SKO Low Voltage (pin 19=0.1V,
+100mA Load at Pin 15)
MICROPHONE AMPLIFIER
Microphone Amp Gain ( Pin 9 =
10mVrms,1KHz)
Microphone Amp Input Resistance RMCI 6.5 10 16

RX

G

RX

∆G

G

RI

RXO

∆V

CR

V

TX

G

TX

∆G

G

TXI

TXO

∆V

ACF

∆V

GSPK 33 34 35 dB

VSKO 2.4 3.0 3.6 Vdc

VSKOH 5.5 Vdc

VSKOL 600 mV

GMCI

2.0

40

-20

100 mV

24.5

4.0
40

-16.5

100 mV

32.5 34 35 dB

6.0

44

-16

6.0
44

-13

150

6.0
75

10

48

-12

32.5

8.0
48

-8.5

dB

dB
dB

µA

kΩ

dB

dB
dB
dB

µA

kΩ

mV
mV
mV

kΩ

kΩ

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(continued)

PARAMETER SYMBOL MIN TYP MAX UNIT

LOGAMPS
RLO Leakage Current
(Pin 8 = VB+1.0V)
TLO Leakage Current
(Pin 6 = VB+1.0V)
Transmit-Receive Switching
Threshold (Ratio of I
20µA - to Switch Tx-Rx
Comparator)
TRANSMIT DETECTOR
XDC Voltage
Idle Mode
Tx Mode
CP2 Current Source ICP2 5.0 10 13
Distortion
Rx Mode
RXI to SKO
(pin 27 = 10mVrms,1KHz)
Tx Mode
MCI to TXO
(Pin 9 = 5mVrms,1KHz)

Note 1:V+=7.5V,CS=0.7V except where noted.
Note 2:Rx mode:pin7=-100µA,pin5=+100µA, except where noted.
Tx mode: pin 5,13=-100µA, pin 7=+100µA, pin 11=0V.
Idle mode: Pin 5=-100µA, pin 7,13=+100µA.
Note 3:Current into a pin designed as +,current out of a pin designed -;
Note 4:Voltage referred to pin 22,Tamb=25°C.

TLI to IRLI - at

ILKRLO 2.0

ILKTLO 2.0

V

ITH

R

T

XDC

XD

XD

25

0

4.0

1.5

2.0

TEMPERATURE CHARACTERISTICS(-20 TO +60°C )

PARAMETER PIN TYP CHANGE UNIT

V+ Supply Current ( V+ 11V,Pin 18 = 0.7V ) 16 -0.2
V+ Supply Current(V+ 11V,Pin 18 = 1.6V ) 16 -0.4
VCC Voltage( V+ = 7.5V ) 20 +0.1
Attenuator Gain ( Max and Min Setting ) +-0.003
Delta RXO,TXO Voltage 4,26 +-0.24
Speaker AMP Gain 15,19 +-0.001
Microphone AMP Gain 9,10 +-0.4
Microphone Amp Input Resistance 9 +0.4
Tx-Rx Switching Threshold (20µA)

5,7 +-0.2

DESIGN GUIDELINES(REF TO FIG. 1)

ATTENUATORS

The transmit and receive attenutors are complementary in function, i.e., when one is at maximum gain the other
is at maximum attenuator, and vice versa. They are never both on or both off. Their main purpose is to control the
transmit and receive paths to provide the half-duplx operation required of a speaker-phone. The attenuators are
controlled solely by the voltage at the ACF pin(pin 25).The ACF voltage is provided by the attenuator control block,

µA

µA

Vdc
Vdc

µA

%

%

%/°C
%/°C
%/°C

dB/°C

%/°C
dB/°C
dB/°C

%/°C
nA/°C

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UTC MC34018 LINEAR INT E G R A TED CIRCUIT

which receives 3 inputs: a) the Rx-Tx comparator, b) the transmit detector comparator, and c)the volume control.
The response of the attenuators is based on the difference of the ACF voltage from VCC, and therefore a simple
method for monitoring the circuit operation is to monitor this voltage difference(referred to as ∆Vacf).If ∆Vacf is
approximately 150 millivolts the circuit is in the receive mode. If ∆Vacf is approximately 75 millivolts the circuit is in
the idle mode, and two attenuators are at gain setting approximately half way(in dB) between their fully on and fully
off positions.
The maximum gain and attenuation values are determined by the three resistors RR,RTX,RRX(referred to
Fig2,3,4).RR affects both attenuators according to its value RELATIVE to RTX and RRX, which is why Fig 4
indicates the variations versus the ratio of the other resistors to RR.(GRX and GTX are the maximum gains, and
ARX and ATX are maximum attenuations).RTX affects the gain and attentuator according to Fig 3.As can be seen
from the figures, the gain difference(from on to off) is a reasonably constant 45dB until the upper gain limit is
approached. A value of 30K is recommended for RR as a starting point, and then RTX and RRX selected to suit the
particular design goals.
The input impedance of the attenuators (at TXI and RXI) is typically 5.0k ohms, and the maximum input signal
which will not cause output distortion is 250mVrms(707mVp-p).The 4300 ohms resistor and 0.01µCapacitor at
RXO(in fig 1)filters out high frequency components in the receive path. This helps minimize high frequency acoustic
feedback problems which may occur if the filter were not present. The filter's insertion loss is a 1.5dB at

1.0kHz.The outputs of the attenuators are inverted from their inputs.
Referring to the attenuator control block, the ∆Vacf voltage at its output is determined by three inputs. The
relationship of the inputs and outputs is summarized in the following truth table.

TX-RX COMP TRANSMIT DET

COMP

Transmit Transmit No Effect 6.0mV Transmit
Transmit Idle No Effect 75mV Idle

Receive Transmit

Receive Idle
As can be seen from the truth table, the Tx-Rx comparator dominates. The transmit detector comparator is
effective only in the receive mode.
The Tx-Rx comparator is in the transmit position when there is sufficient transmit signal present over and
above any receive signal. The transmit detector comparator then determined whether the transmit signal is a result
of background noise(1 relatively stable signal),or speech which consists of bursts.If the signal is due to background
noise, the attenuators will be put into the idle mode(∆Vacf=75mV).If the signal consists of speech, the attenuator will
be switched to the transmit mode(∆Vacf=6.0mV).A further explanation of this function will be found in the section on
the transmit detector circuit.
The Rx-Tx Comparator is in the receive position when there is sufficient receive signal to overcome the
background noise AND any speech signals. The ∆Vacf voltage will now be 150mV IF the volume control is at the
maximum position, i.e. VLC(pin 24)=VB. If VLC is less than Vb, the gain of the receive attenuator, will vary in a
complementary manner as shown in fig 5.It can be seen that at the minimum recommended operating
level(VLC=0.55VB) the gain of the transmit atternuator is actually greater than that of the receive attenuator. The
effect of varying VLC is to vary ∆Vacf, with a resulting variation in the gains of the attenuators, Fig 6 shows the
gain variation with ∆Vacf.
The capacitor at ACF(pin 25) smoothes the transition between operating modes. This keeps down any "clicks"
in the speaker or transmit signal when the ACF voltage switches.
The gain separation of the two attenuators can be reduced from the typical 45dB by adding a resistor between
pin 20(VCC) and pin 25(ACF).The effect is a reduction of the maximum ∆Vacf voltage in receive mode, while not
affecting ∆Vacf in the transmit mode. as an example, adding a 12 k ohms resistor will reduce ∆Vacf by approximately
15mV(to 135mV).decrease the gain of the receive attenuator by approximately 5.0dB, and increase the gain of the
transmit attenuator by a similar amount. If the circuit requires the receive attenuator gain to be +6.0dB in the receive
mode, RRX must be adjusted (to 27k ohms) to re-establish this value. This change will also increase the receive
attenuator gain in the transmit mode by a similar amount. The resistor at TLI may also require
changing to reset the sensitivity of the thansmit level detector.

VOLUME

CONTROL

Affects ∆Vacf
Affects ∆Vacf

∆VACF MODE

50-150mV Receive

50-50mV Receive

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UTC MC34018 LINEAR INT E G R A TED CIRCUIT

LOG AMPLIFIERS(Transmit and Receive level Detectors)

The logs amps monitor the levels of tharsmit and receive signal, so as to tell the Tx-Rx comparator which mode
should be in effect. The input signals are applied to the amplifiers(at TLI and RLI) through AC coupling capacitors
and current limiting resistors. The value of these components determines the sensitivity of the respective
amplifiers ,and has an effect on the switching times between transmit and receive modes. The feedback elements for
the amplifier are back-to-back diodes which provide a logarithmic gain curve, thus allowing operation over a wide
range of signal levels. The outputs of the amplifiers are rectified, having a quick rise time and a slow decay time. The
rise time is determined by the external resistor and capacitor, and is on the order of a fraction of a second. The
switching time is not fixed, but depends on relative values of the transmit and receive signals, as well as these
external components. Fig 7 indicates the DC transfer characteristics of the log amps, and Fig 8 indicates the transfer
characteristics with respect to an AC input signal the DC level at TLI,RLI,TLO, and RLO
is approximately VB.
The Tx-Rx comparator responds to the voltages at TLO and RLO, which in turn are functions of the currents
sourced out of TLI and RLI, respectively. If an offset at the comparator input is desired, e.g. to prevent noise from
switching the system, or to give preference to either the transmit or receive channel, this may be achieved by biasing
the appropriate input(TLI or RLI).A resistor to ground will cause a DC current to flow out of that input, thus forcing the
output of that amplifier to be biased slightly higher than normal. This amplifier then becomes the preferred one in the
system operation. Resistor values from 500k to 10M ohms are recommended for this purpose.

SPEAKER AMPLIFIER

The speaker amplifier has a fixed gain of 34dB(50V/V),and is noninverting. The input impedance is nominally
22 k ohms as long as the output signal is below that required to activate the peak limiter. The Fig 9 indicates the
typical output swing available at SKO(pin 15).Since the output current capability is 100mA,the lower curve is limited
to 1 5.0Volt swing. The output impedance depends on the output signal level and is a relatively low as long as the
signal level is not near maximum limits. At 3 Vp-p the output impedance is less than 0.5 ohms, and at 4.5Vp-p it is
less than 3 ohms. The output is short circuit protected at approximately 300 mA.
When the amplifier is over driven, the peak limiter causes a portion of the input signal to be shunted to ground,
in order to maintain a constant output level. The effect is that of a gain reduction caused by a reduction of the input
impedance (at SKI) to a value not less than 2.0k ohms.
The capacitor at pin 17(AGF) determines the response time of the peak limiter circuit. When a large input
signal is applied to SKI, the voltage at AGC(pin 17) will drop quickly as a current source is applied to the external
capacitor. When the large input signal is reduced, the current source is turned off, and an internal 110k ohms
resistor discharges the capacitor so that the voltage at AGC can return toots normal value(1.9Vdc).The capacitor
additionally stabilizes the peak limiting feedback loop.
If there is a need to mute the speaker amplifier without disabling the rest of the circuit, this may be
accomplished by connecting a resistor from the AGC pin to GND.A 100k ohms resistor will reduce the gain by 34dB
(0dB from SKI To SKO), and a 10k ohms resistor will reduce the gain by almost 50dB.

TRANSMIT DETECTOR CIRCUIT

The transmit detector circuit, also known as the background noise monitor, distinguishes speech(which
consists of bursts) from the background noise( a relatively constant signal).It does this by storing a voltage level,
representative of the average background noise, in the capacitor at CP1(pin 11).The resistor and capacitor at this
pin have a time constant approximately 5 second(in fig 1).The voltage at pin 1 is applied to the inverting input of the
transmit detector comparator. In the absence of speech signal, the noninverting input receiving the same as voltage
level minus an offset of 36mV.In this condition, the output transistor turned off, and the voltage at XDC(pin 23) will be
at GND. If the Tx-Rx comparator is in the transmit position, the attenuators will be in the idle mode(∆Vacf=75mV).
When speech is presented to the microphone, the signal burst appearing at XDI reaches the noninverting input of
the transmit detector comparator before the voltage at the inverting input can change, causing the output to switch
high, driving the voltage ad XDC up to approximately 4Volts.This high level causes the attenuator control block to
switch the attenuators from the idle mode to the transmit mode(assuming the Tx-Rx comparator is in the transmit
mode).As long as the speech continues to arrive, and is maintained at a level above the background, the voltage at
XDC will be maintained at a high level, and the circuit will remain in transmit mode. The time constant of the

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UTC MC34018 LINEAR INT E G R A TED CIRCUIT

components at XDc will determine how much time the circuit requires to return to the idle mode after the cessation of
microphone speech signals, such as occurs during the normal pauses in speech.
The series resistor and capacitor ax XDI(pin 13) determine the sensitivity of the transmit detector circuit. Fig 10
indicates the change in DC voltage levels at CP2 and CP1 in response to a steady state sine wave applied at the
input of 0.068µF capacitor and 4700 ohms resistor( the voltage change at CP1 is 2.7 times greater than the
change at P2).Increasing the resistor, or lowing the capacitor, will reduce the response at these pins. The first
amplifier(between XDI and CP2) is logarithmic in order that this circuit be able to handle a wide range of signal
levels(or in other words, it responds equally well to people who talk quietly and to people who shout).Fig 7 indicates
the DC transfer characteristic of the log amp.
Fig 11 indicates the response at Pins 11,12, and 23 to a varying signal at the microphone. The series of events
in Fig 11 is as follows:

1) CP2 follows the peaks of speech signals, and decays at a rate determined by the 10µA current source and
the capacitor at this pin.

2) CP1 increases at a rate determined by the RC at this pin after CP2 has made a positive transition. It will
follow
the decay pattern of CP2.

3) The noninverting input of the transmit detector comparator follows CP2, gained up by 2.7, and reduced by an
offset of 36mV.This voltage, compared to CP1, determines the output of the comparator.

4) XDC will rise quickly to 4Vdc in response to a positive transition at CP2, but will decay at a rate determined
by
the RC at this pin. When XDC is above 3.25Vdc, the circuit will be in transmit mode. As it decays towards
GND, the attenuators are taken to the idle mode.

MICROPHONE AMPLIFIER

The microphone amplifier is noninverting, has an internal gain of 34db(50V/V), and a nominal input impedance
of 10k ohm. The output impedance is typically less than 15 ohms. The maximum p-p voltage swing available at the
output is approximately more than what is required in most applications. The input at MCI should be AC coupled to
the microphone so as to not upset the bias voltage. Generally, microphone sensitivity may be adjusted by varying
the 2K microphone bias resistor, rather than by attempting to vary the gain of the amplifier.

POWER SUPPLY

The voltage supply for the UTC MC34018 at V+ should be in the range of 6.0 to 11 Volts, although the circuit
will operate down to 4.0Volts>the voltage can be supplied either from TIP and RING, or from a separate supply. The
required supply current, with no signal to the speaker, is shown in Fig 11. The upper curve indicates the normal
operating current when
power levels to a 25 ohms speaker. Fig 13 also indicates the minimum supply voltage required to provide the
indicated power levels. The peak in power supply current at 5.0-5.0 volts occurs as the VCC circuit comes into
regulation.
It is imperative that the V+ supply be a good AC GND for stability reasons. If this pin is not well filtered( by a
1000μF capacitor at the IC), any variation at V+ caused by the required speaker current flowing through this pin can
cause a low frequency oscillation. The result is usually that the circuit will cut the speaker signal on and off at the
rate of a few hertz. Experiments have shown that only a few inches of wire between the capacitor is not physically
adjacent to the IC. It is equally imperative that both ground pins(pin 14 and 22) have a low loss connection to the
power supply ground.

VCC

VCC is a regulated output voltage of 5.4+-0.5 volts. Regulation will be maintained as long as V+ is typically 80
mV greater than the regulated value of VCC. Up to 3 milliamps can be sourced from this supply for external use. The
output impedance is less than 20 ohms.
The 47µF capacitor indicated for connection to pin 20 is essential for stability reasons, It must be located
adjacent to the IC.
If the circuit is deselected (see section on chip select), the VCC voltage will go to 0 volts.

CS

is at a logic "0".Fig 13 indicates the average Dc current required when supplying various

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UTC MC34018 LINEAR INT E G R A TED CIRCUIT

If UTC MC34018 is to be powered from a regulated supply( not the Tip and Ring lines) of less than 6.5 volts,
the configuration of Fig 14 may be used so as to ensure to that VCC is regulated<the regulated voltage is applied to
both V+ and VCC, with
available when the circuit is used in this manner).Fig 15 indicates the supply current used by the configuration, with
no signal at the speaker. When a signal is sent to the speaker, the curves of Fig 13 apply.

VB

VB is a regulated output voltage with a nominal value of 2.9 +-0.4volts.It is derived from VCC and tracks it,
holding a value of approximately 54% of VCC.1.5milliamps can be sourced from this supply at a typical output
impedance of 250 ohms.
The 47µF capacitor indicated for connection to the VB pin is required for stability reasons, and must be
adjacent to the IC.
If the circuit is deselected(see section on Chip Select), the VB voltage will go to 0 Volts.

CHIP SELECT

The CS pin allows the chip to be powered down anytime its functions are not required. A logic "1" level in the
range of 1.6V to 11V deselects the chip and the resulting supply current (at V+) is shown in Fig 12.The input
resistance at pin
deselected. Leaving Pin 18 open is equivalent to a logic "0"(chip enabled).

SWITCH TIME

The switch time of the speakerphone circuit depend not only the various external components, but also on the
operating condition of the circuit at the time a change os taken effect. For example, the switching time form idle to
transmit is generally quicker than the switching time from receive to transmit(or transmit to receive).
The components which most significantly affect the timing between the transmit and receive modes are those
at pins 5 (transmit turn-on),6(transmit turn-off),7(receive turn -on),8(receive turn off).These four timing functions are
not independent, but interact since the Tx-Rx comparator operates on a relative Tx-Rx comparison, rather than on
absolute value. The components at pins 11,12,13,23 affect the timing from the transmit mode to the idle mode.
Timing from the idle mode to transmit mode is relatively quick(due to the quick charging of the various
capacitors),and is not greatly affected by the component values. Pin 5-8 do not affect the idle to transmit timing
since the Tx-Rx comparator must already be in the transmit mode for this to occur.
The following table provides a summary of the effect on the switching time of the various components,
including the volume control:

COMPONENTS TX TO RX RX TO TX TX TO IDLE

RC@pin5 Moderate Significant No effect
RC@pin6 Significant Moderate No effect
RC@pin7 Significant Moderate No effect
RC@pin8 Moderate Significant No effect

RC@pin11 No effect Slight Moderate

C@pin12 No effect Slight Significant
RC@pin13 No effect Slight Slight
RC@pin23 No effect Slight Significant

V@pin24 No effect Moderate No effect

C@pin25 Moderate Moderate Slight

Additionally ,the following should be noted:

1) RCs at pin 5 and 7 have a dual function in that they affect the sensitivity of the respective log amplifiers, or in
other words, how loud the speech must be in order to gain control of the speaker phone circuits.

2) The RC at pin 13 also has a dual function in that it determines the sensitivity of the transmit detector circuit.

3) The volume control affects the switching speed, and the relative response to the transmit signals, in following
manner: when the circuit is in the receive mode, reducing the volume control setting increases the signal at
TXO, and consequently the signal to the TLI pin. Therefore a given signal at TXI will switch the circuit into the
transmit mode quicker at low volume settings.
All of the above mentioned times will change significantly by varying the amplitude of the input signals, as well

CS

held at a logic "1" so as to turn off the internal regulator( the Chip Select function is not

CS

is greater than 75 k ohms. The VCC and VB regulated voltage go to 0 volts when the chip is

UTC UNISONIC TECHNOLOGIES CO., LTD.

QW-R108-006,A

9

UTC MC34018 LINEAR INT E G R A TED CIRCUIT

as by varying the external components.

APPLICATIONS INFORMATION

The UTC MC34018 speakerphone IC is designed to provide the function additionally required when a
speakerphone is added to a standard telephone. The IC provides the necessary relative level detection and
comparison of the speech signals provided by the talkers at the speakerphone(near end speaker) and at the distant
telephone(far end speaker).
The UTC MC34018 is designed for use with an electorate type microphone a 25 ohms speaker, and has an
output power capability of 100mW.All external components surrounding this device are passive, however, this IC
does require additional circuitry to interface the TIp and Ring telephone lines. Two suggested circuits are shown in
the data sheet.
Fig 16 depicts a configuration which does not include a handset, dialer, or ringer. The only controls are S1(to
make the connection to the line),S2(a "privacy" switch),and the volume control. It is meant to be used in parallel with
a normal telephone which has dialing and ringing functions.
Fig 17 depicts a means of providing logic level signal that indicate which mode of operation the UTC MC34018
is in. Comparator A indicates whether the circuit is in receive or transmit mode and comparator B indicates(when in
transmit/idle mode) whether the circuit is in the transmit or idle mode. The UTC LM393 dual comparator is chosen
because of its low current requirement (<1.0mA), low voltage requirement (as low as 2.0volts), and low cost.

TRANSMIT

OUTPUT

2k

Ω

0.068 µF

MIC

0.068 µF

F

µ

1.0

4.7k

Ω

0.1 µF

3.3k

0.05

0.068

µ

F

4.7k

Ω

VB

12kΩ59k

Ω

µ

F

10k

9

MCI

Ω

TLI

5

VB

TLO

6

Ω

2.2M

RTI

7

VB

10 13 12 11 23 18 16

Ω

MIC AMP

VB

VB

500

Ω

TRANSMIT
LOG AMP

RECEIVE

AMP

RECEIVE/TRANSMIT

COMP

500

Ω

RLO VB VLC ACF TXI RR TXO RRXRXIRTX RXO SKI SKG SKO

1.0

µ

F

2.2M

Ω

33kΩ56k

Attenuator

control

Vcc

VB

regulator

VB

Ω

20k

Ω

24k

4.7 µF 47 µF

Ω

transmit

attenuator

µ

F47 µF

4.7

Vcc

Vth

(36mV)

Ω

30k

Ω

91k

F

Ω

Ω

µ

47

200k

100k

Vcc

transmit

receive

attenuator

detector comp

26k

19262827412325218

4.3kΩ18k

Ω

0.05

µ

0.1

µ

F0.1 µF

0.01

F

µ

F

Ω

Speaker

amp

Vcc

regulator

limiter

DC line input

1000 µF

CSXDCCP1CP2XDIMCO

V+

VCC

Vcc

5.4V

GND

AGC

peak

Receive input

µ

F

47

20

22

VB

µ

F

1.0

17

151424

47 µF

25

Ω

Fig 1 Test circuit

UTC UNISONIC TECHNOLOGIES CO., LTD.

QW-R108-006,A

10

UTC MC34018 LINEAR INT E G R A TED CIRCUIT

Fig 2 Transmit attenuator versus RTX

+20

+10

0

-10

-20

-30

dB

Max Attenuation

-40

Vacf=150mV

-50
RR=30k ohms

VLC=VB

-60

-70

10k 100k 1M

Fig 4 Gain and attenuation versus

+20

GRX vs RRX/RR

Vacf=150mV

+10

0

-10

-20

-30

dB

ARX vs RRX/RR

-40

-50

-60

-70

0.1 1.0 10

Resisrtor Ratio

Vacf=6.0mV

RTX (ohms)

VLC=VB

Ratio

Max Gain

Vacf=6.0mV

GTX vs RTX/RR

Vacf=6.0mV

ATX vs RTX/RR

Vacf=150mV

Fig 3 Receive attenuator versus RRX

+20

+10

0

-10

-20

-30

dB

-40

-50

-60

-70

+10

0

-10

-20

-30

-40

Max Gain

Vacf=6.0mV

Max Attenuation

RR=30k ohms

VLC=VB

1k 10k 100k

RRX (ohms)

Vacf=150mV

Usable range

Fig 5 Attenuation Gain versus VLC

RRX=18k ohms
RTX=91k ohms

RR=30k ohms

Circuit in

receive

mode

0.2

GTX GRX

Mimimum

recommended

level

0.4 0.8 1.00

0.6

UTC UNISONIC TECHNOLOGIES CO., LTD.

QW-R108-006,A

11

UTC MC34018 LINEAR INT E G R A TED CIRCUIT

+10

Fig 6 Attenuator Gain vs Vacf

Fig 7 Log Amp Transfer Characteristics

250

0

-10

dB

-20

-30

-40
0

150

120

90

60

Output Channel(mV)

30

0

0 20406080

GTX

RR=30k ohms
RTX=91k ohms
RRX=18k ohms

20 40 60 80 100 120 140 160

Vacf(mV)

Fig 8 Log Amp Transfer Characteristics

R=2700 ohms

µ

F

C=0.1

(RLI,TLI)

CR

Input Votage

(@ 1.0kHz)

VB

Input Voltage(mVp-p)

GRX

R=4700 ohms

C=0.068

R=4700 ohms

C=0.068

µ

µ

F

(RLO,TLO)

200

150

100

Output Channel(mV)

50

0

0 -20 -40 -60 -80

Fig 9 Speaker Amp Output vs Supply Voltage

10.0

F

8.0

6.0

4.0

VSKO MAX(p-p Volts)

2.0

0

Input

Current

(RLI,TLI,XDI)

VB

DC Input Current( µA)

4.0 5.0 6.0 7.0 8.0 9.0 10.0 11.03.02.0

V+(Volts)

No load

Output

Voltage

(RLO,TLO,CP2)

25 ohms load

Fig 11 Transmit Detector operation

Input Signal

(@ MCI)

CP2(pin 12)

Solid line=CP1(pin11)
Dotted line=Voninverting
Input of transmit detectot

Comparator

XDC(pin 23)

V1=200mV

2.7 x V1

Slope=0.5V/sec

4 Volts

36mV

UTC UNISONIC TECHNOLOGIES CO., LTD.

QW-R108-006,A

12

UTC MC34018 LINEAR INT E G R A TED CIRCUIT

500

400

300

200

CP1,CP2 Voltage Channel(mV)

100

Fig 10 Response At CP1 and CP2

DVCP1

DVCP2

0

0 50 100 150 250200

VMCO(mVrms)

Fig 12 Supply Current vs Supply Voltage

9.0

8.0

7.0

6.0

5.0

IV+(mA)

4.0

3.0

2.0

1.0

0.0

3.0

4.0 5.0 6.0 7.0 8.0 9.0 10 11

CS=0

VSKO=0mVrms

CS=1

V+(Volts)

Fig 13 Supply Current vs Supply Voltage vs

35

30

25

IV+(mA)

20

15

10

4.0 5.0 6.0 7.0 8.0 9.0 10 113.0

Speaker Power

V+(Volts)

100mW

80mW

50mW

20mW

10mW

5mW

Fig 15 Supply Current vs Supply Voltage

25

20

15

Is(mA)

10

5

0

4.03.0

Available

operating Range

5.0 6.0 7.0 8.0

Vs(Volts)

Fig 14 Alternate Power supply Configuration

18

UTC

MC34018

20 16 22

100 mF

VS

(Regulated Supply)

UTC UNISONIC TECHNOLOGIES CO., LTD.

QW-R108-006,A

13

UTC MC34018 LINEAR INT E G R A TED CIRCUIT

220k

Ω

68k

F0.01

µ

47kΩ6.8k

0.01

Ω

F

µ

8.2kΩ8.2k

VB 4.7k

MIC

2k

Speaker

F

µ

0.05

Ω

47 µF

Volume
Control

4.7k

Ω

2.7k

Ω

0.1 µF
470k

F

Ω

Ω

µ

33k

47k

10

0.1 µF

S2

TXI MCO XDI TXO TLI CP1 ACF AGC V+ CS RLI RXI

MCI

9

SKO

15

SKG

14

VB

Ω

20k

24k

Ω

S1

F

µ

Ω

Ω

0.01

Ω

Ω

3 10 13 4 5 11 25 17 16

Ω

F

15k

µ

8.2k

Ω

F

µ

2.2k

0.068

1000

Ω

3.3k

F

µ

0.068

0.068

Ω

100k

mF

Ω

47k

Vcc VB

47 µF

Ω

0.05

µ

F

4700pF

Hook

Switch

0.01 µF

F

µ

4.7

4700pF

F

µ

1.0

Ω

470k

UTC MC34018

24 21 20 2 1 28 26 19 12

F

Ω

µ

0.05

4.7 µF 4.7 µF

F

µ

0.01

47 µF 47 µF

91kΩ30kΩ18k

4.3k

Ω

Fig 16 basic Line powered Speakerphone

T

R

Ω

470k

Ω

47k

Ω

22k

F

µ

0.068

18 7 27

23 6 8 22

200k

Ω

3.3k

Ω

F

µ

0.1

2.2MΩ2.2M

F

µ

1.0

GNDRLOTLOXDCCP2SKIRXORRXRRRTXVccVBVLC

Ω

F

µ

1.0

UTC

MC34018

8 6 20 21 23

56k56k

+

-

Tx/Idle

+

-

Rx

Tx

Idle

Fig 17 Digital Transmit/Idle/Receive Indication

UTC UNISONIC TECHNOLOGIES CO., LTD.

QW-R108-006,A

14