MC34118 Unisonic Technologies, MC34118 Datasheet - Page 11

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

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UTC MC34118 LINEAR INTEGRATED CIRCUIT
MICROPHONE AMPLIFIER
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
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
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
The microphone amplifier( Pins 10, 11) has the non-inverting input internally connected to VB while the inverting
The two hybrid amplifiers( at HTO+, HTO-, and HTI), in conjunction with an external transformer, provide the
The operation of the filter circuit is determined by the external components. The circuit within the UTC MC34118,
UNISONIC TECHNOLOGIES CO., LTD.
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QW-R108-007,B
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