UTCMC34118 查看數據表（PDF） - Unisonic Technologies

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UTCMC34118

VOICE SWITCHED SPEAKER-PHONE CIRCUIT

Unisonic Technologies 

UTCMC34118 LINEAR INTEGRATED CIRCUIT

VOLUME CONTROL

The volume control input at VLC(pin 13), is sensed as a voltage with respect to VB. The volume control affects the

attenuators only in the receive mode. It has no effect in the idle or transmit modes. When in the receive mode, the

gain of the receive attenuator will be +6dB, and the gain of the transmit attenuator will be -46dB, only when VLC is

equal to VB. As VLC is reduced below VB, the gain of the receive attenuator is reduced, and the gain of the transmit

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

The dial tone detector is a comparator with one side connected to the receive input(RXI) and the other input

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.

The purpose of this circuit is to prevent the dial tone( which would be considered as continuous noise) from fading

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

The AGC circuit affects the circuit only in the receive mode, and only whenn the supply voltage( Vcc) is less than

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

UNISONIC TECHNOLOGIES CO., LTD. 9

QW-R108-007,A

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