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

MICROPHONE AMPLIFIER

The microphone amplifier( Pins 10, 11) has the non-inverting input internally connected to VB while the inverting

input and the output are pinned out. Unlike most op-amps., the amplifier has an all-NPN output stage, which

maximizes phase margin and gain bandwidth. This feature ensures stability at gains less than unity, as wide range of

reactive loads. The open loop gain is typically 80Db(f<100Hz), and the gain bandwidth is typically 1MHz. The

maximum p-p output swing is typically 1 volt. less than Vcc with an output impedance of <10Ω until current limiting is

reached( typically 1.5mA). Input bias current at MCI is typically 40nA out of the pin. The muting function( Pin 12),

when activated, will reduce the gain of the amplifier to ~-39dB( with RMI=5.1kΩ) by shorting the range of ground and

Vcc. If the mute function is not used, the pin should be grounded.

HYBRID AMPLIFIER

The two hybrid amplifiers( at HTO+, HTO-, and HTI), in conjunction with an external transformer, provide the

two-to-four wire converter for interfacing to the telephone line. The gain of the first amplifier( HTI to HTO-) is set by

external resistors( gain = -RHF/RHI in Block Diagram), and its output drives the second amplifier, the gain of which is

internally set at -1. Unlike most op-amps., the amplifiers have an all- NPN output stage, which maximizes phase

margin and gain-bandwidth. This feature ensures stability at gains less than unity, as with a wide range of reactive

loads. The open loop gain of the first amplifier is typically 80dB, and the gain-bandwidth of each amplifier is ~1MHz.

The maximum p-p output swing is typically 1.2 volts. less than Vcc with an output impedance of <10Ω until current

limiting is reached( typically 8mA). The output current capability is guaranteed to be a minimum of 5mA. The bias

current at HTI is typically 30nA out of the pin. The connections to the coupling transformer are shown in the Block

Diagram. The block labeled ZBal is the balancing network necessary to match the line impedance.

FILTER

The operation of the filter circuit is determined by the external components. The circuit within the UTC MC34118,

from pins FI to FO is a butter with a high input impedance(>1MΩ), and a low output impedance(<50Ω). The

configuration of the external components determines whether the circuit is a high-pass filter( as shown in Block

Diagram), a low-pass filter, or a band-pass filter. As a high-pass filter, with the components shown in Figure 6, the

filter will keep out 60Hz( and 120Hz) hum which can be picked up by the external telephone lines. As a low-pass

filter, with the components shown in Figure 7, it can be used to roll off the high end frequencies in the receive circuit,

which aids in protecting against acoustic feedback problems, with an appropriate choice of an input coupling

capacitor to the low-pass filter, a band pass filter is formed.

UTC

UNISONIC TECHNOLOGIES CO., LTD. 11

QW-R108-007,A

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