Description.
PBL 38570 is a monolithic integrated speech transmission circuit for use in electronic telephones. It is designed to accomodate either a low impedance dynamic or an electret microphone. A separate input for DTMF dialling tones that is controlled by a mute signal, and a signal summing point at the transmitter input, are available.

Key features.
• Minimum number of external components, 7 capacitors and 11 resistors.
• Easy adaption to various market needs.
• Mute control input for operation with DTMF - generator.
• A separate input for DTMF tones controlled by mute.
• Transmitter and receiver gain regulation for automatic loop loss compensation.
• Extended current and voltage range 5 - 130 mA, down to 2 V.
• Differential microphone input for good balance to ground.
• Balanced receiver output stage.
• Stabilized DC - supplies for low current CMOS diallers and electret microphones.
• 18 - pin DIP and 20 - pin SO packages.
• Short start up time.
• Excellent RFI performance.