UTCMC34018 查看數據表（PDF） - Unisonic Technologies

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UTCMC34018

VOICE SWITCHED SPEAKER-PHONE CIRCUIT

Unisonic Technologies 

UTCMC34018 LINEAR INTEGRATED 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 CS is at a logic "0".Fig 13 indicates the average Dc current required when supplying various

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.

UTC

UNISONIC TECHNOLOGIES CO., LTD. 8

QW-R108-006,A

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