January 2000 TOKO, Inc.

Page 9

TK10651

COMPRESSOR

By placing the data input pin following the compressor

circuit, a data signal can be transmitted without being

compressed. Audio from the microphone can be connected

directly to the IC, because it passes through the built-in

microphone amplifier (the gain is adjustable). Since there is

a built-in limiter to prevent overmodulation, it is not neces-

sary to add an external Instantaneous Deviation Control

(IDC) circuit; furthermore, a Low Pass Filter (LPF) up to the

third order can be constructed using the buffer amplifier.

When a data signal is being transmitted, the unneeded

audio can be cut by engaging the mute switch.

EXPANDER

A wide range of applications are made possible because all

of the input amplifier pins are accessible. A LPF of up to the

third order can be constructed at the input, and with an

external resistor, it can be used as an amplifier. If the data

out pin is used for the output, a data signal can be extracted

without passing through the expander. During data trans-

mission, the audio signal system can be inhibited by using

the mute switch.

APPLICATION INFORMATION

COMPRESSOR MICROPHONE AMPLIFIER

The input pin connects to the reference voltage through a

100 k

Ω bias resistor, therefore external bias is not neces-

sary. The microphone amplifier gain can be adjusted by

connecting an external resistor to NF pin 7. The gain is

highest when no resistor is added, and the standard input

level is 3 mV. When an external resistor of 9.1 k

Ω is added,

the standard input level is about a 10 mV; when the external

resistor value is 68 k

Ω, the standard input level is 30 mV.

The input can accommodate a variety of microphones by

adjusting the gain to match the microphone's output volt-

age.

The user should set the gain and input level so that the

output level at pin 3 is normally 300 mV (standard level).

8

+

-

51 k

3.3 k

7

COMP IN

COMP NF

100 k

~3 mV

8

+

-

7

51 k

3.3 k

9.1 k

COMP IN

100 k

COMP NF

~10 mV

7