TI Carbon Transmitter Model for Use in Computer-Sided Analysis of Telephone Set Transmission Characteristics

Computer-aided optimization of the transmission characteristics of telephone sets requires that accurate models be obtained for all transmission-related telephone set components. A carbon transmitter model has been derived for this purpose. This model has been used in a telephone set transmission analysis computer program, and good agreement between computed and measured transmission characteristics was obtained. The dc V-I characteristic of the carbon transmitter is nonlinear. This nonlinearity must be taken into account in the dc model so that, in the transmission analysis program, the operating point of the transmitter can be determined, as well as the operating points of any nonlinear telephone speech network components, e.g., silicon carbide varistors. Thus, the dc model is a voltage-dependent resistance. The ac model is similar to that of a vacuum-tube triode, consisting of a Thevenin-equivalent resistance and voltage source. The voltage source is dependent on the amplitude of the force acting on the carbon granules because of the acoustic excitation of the transmitter. This 1301