Signal level expansion apparatus as for a telecommunications system

Abstract

A signal level expansion system for use in a telephone device is described which includes a level expansion circuit and an optional microphone enclosure. The circuit includes a voltage divider circuit which is used as a variable attenuator. The voltage divider has a junction field effect transistor (JFET) in its takeoff leg. The signal provided by the voltage divider is applied to an amplifier and then fed to a switch which detects voice signals. When a voice signal is detected having a level above a predetermined threshold, a timing circuit is energized. The timing circuit is connected to the JFET and, when energized, tends to increase the resistance in the takeoff leg of the voltage divider, increasing the signal level applied to the amplifier. The microphone enclosure surrounds the sides of the microphone with layers of rigid and resilient materials. These materials tend to attenuate all sound signals except those incident on the top of the microphone, which is positioned to receive speech signals from a user.