PBL 38541 is a monolithic integrated speech transmission circuit for use in electronic telephones or in any other line interface application. It has a high settable supply current for auxiliary functions, up to 6.0 mA (at high line currents). The circuit is designed to accommodate either a low impedance dynamic or an electret microphone. The microphone can be muted separately. Payphone signaling and DTMF dialing tones have a separate input that is controlled by a mute signal. A signal summing point is available at the transmitter input. An internally preset line length compensation can be adjusted with external resistors to fit into different current feed systems, such as 48 V, 2 x 200 ohms, 48 V, 2 x 400 ohms, and 48 V, 2 x 800 ohms. The line length compensation can be shut off in either high or low gain mode. Application dependent parameters such as line balance, side tone level, transmitter and receiver gains, and frequency responses are set independently by external components, which means easy adaptation to various market needs. The setting of the parameters, if carried out in a certain order, will counteract the interaction between the settings. The circuit provides four different DC supplies to feed microphones, dialers, and other more current-consuming functions like handsfree systems.
