IL34118N View Datasheet(PDF) - IK Semicon Co., Ltd

Part Name

Description

MFG CO.

IL34118N

Voice Switched Speakerphone Circuit

IK Semicon Co., Ltd 

IL34118

Figure 4. CT Attenuator Control Block Circuit

MICROPHONE AMPLIFIER

The microphone amplifier (Pin 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 well

as with a wide range of reactive loads. The open loop

gain is typically 80 dB (f<100 Hz), and the gain-

bandwidth is typically 1.0 MHz. The maximum p-p

output swing is typically 1.0 volt less than VCC with an

output impedance of <10  until current limiting is

reached (typically 1.5 mA). Input bias current at MCI is

typically 40 nA out of the pin.

Figure 5. Microphone Amplifier and MUTE

HYBRID AMPLIFIERS

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

Figure 8), and its output drives the second amplifier, the

gain of which is internally set at -1.0. 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 well

as with a wide range of reactive loads. The open loop

gain of the first amplifier is typically 80 dB, and the gain

bandwidth of each amplifier is 1.0 MHz. The maximum

p-p output swing of each amplifier is typically 1.2 volts

less than VCC with an output impedance of <10  until

current limiting is reached (typically 8.0 mA). The output

current capability is guaranteed to be a minimum of

5.0 mA. The bias current at HTI is typically 30 nA out of

the pin.

The connections to the coupling transformer are

shown in the Expanded Logic Diagram (Figure 8). 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 IL34118,

from pins FI to FO is a buffer with a high input

impedance (>1.0 M), and a low output impedance

(<50 ). The configuration of the external components

determines whether the circuit is a high-pass filter (as

shown in Figure 8), a low-pass filter, or a band-pass filter.

Figure 6. High Pass Filter

The muting function (Pin 12), when activated, will

reduce the gain of the amplifier to = -39 dB (will RMI

= 5.1 K) by shorting the output to the inverting input

(see Figure 5). The mute input has a threshold of 1.5 volt,

and the voltage at this pin must be kept within the range

of ground and VCC. If the mute function is not used, the

pin should be grounded.

As a high pass filter, with the components shown in

Figure 6 the filter will keep out 60 Hz (and 120 Hz) hum

which can be picked up by the external telephone lines.

2013, January, Ver. 02

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