MC34118 Unisonic Technologies, MC34118 Datasheet - Page 9

• Manufacturer Part Number: MC34118
• Description: Voice Switched Speaker Phone Circuit
• Manufacturer: Unisonic Technologies

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UTC MC34118 LINEAR INTEGRATED CIRCUIT
attenuator is increased, such that their sum remains constant. Changing the voltage at VLC changes at CT( see the
attenuator Control Block section), which in turn controls the attenuators. The volume control setting does not affect
the maximum attenuator input signal at which noticeable distortion occurs. The bias current at VLC is typically 60 nA
out of the pin, and does not vary significantly with the VLC voltage or with VCC.
DIAL TONE DETECTOR
connected to VB with a 15mV offset( see Figure 4). If the circuit is in the receive mode, and the incoming signal is
greater than 15Mv(10 mVrms). The comparator’s output will change, disabling the receive idle mode. The receive
attenuator will then be at a setting determined solely by the volume control.
away as the circuit would have the tendency to switch to the idle mode. By disabling the receive idle mode, the dial
tone remains at the normally expected full level.
AGC
3.5 volts. As Vcc falls below 3.5 volts., the transmit path attenuation changes such that the sum of the transmit and
receive gains remains constant. The purpose of this feature is to reduce the power) and current) used by the
speaker when a line-powered speakerphone is connected to a long line, where the available power is limited. By
reducing the speaker power, the voltage sag at Vcc is controlled, preventing possible erratic operation.
ATTENUATOR CONTROL BLOCK
The Attenuator control block has the seven inputs described below:
*The output of the comparator operated by RLO2 and TLO2( microphone/ speaker side), designated C1.
*The output of the comparator operated by RLO1 and TLO1( Tip/ Ring side), designated C2.
*The output of the transmit background noise monitor, designated C3.
*The output of the receive background noise monitor, designated C4.
* The volume control
* The dial tone detector
* The AGC circuit
The single output of the control block controls the two attenuators. The effect of C1~C4 is as follows:
UTC
The dial tone detector is a comparator with one side connected to the receive input(RXI) and the other input
The AGC circuit affects the circuit only in the receive mode, and only whenn the supply voltage( Vcc) is less than
The purpose of this circuit is to prevent the dial tone( which would be considered as continuous noise) from fading
C1
Tx
Tx
Rx
Rx
Tx
Tx
Rx
Rx
UNISONIC TECHNOLOGIES CO., LTD.
C2
Rx
Rx
Rx
Rx
Tx
Tx
Tx
Tx
INPUTS
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C3
1
Y
Y
X
0
0
0
X
C4
X
Y
Y
1
X
0
0
0
OUTPUT MODE
Slow Idle
Slow Idle
Transmit
Slow Idle
Slow Idle
Fast Idle
Fast Idle
Receive
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