Abstract: An amplifier includes a differential amplifier stage, a voltage amplification stage and a power output stage. The bias level of the output stage is proportional to current through the voltage amplification stage. The voltage amplification stage includes a current mirror whereby controlled current through a first leg of the current mirror controls current through the remaining, second leg, which, in turn, determines the bias level of the power output stage. Control circuitry senses a parameter of the amplifier, such as DC bias or input signal level to generate a control signal which is applied to the first leg of the current mirror to thereby control bias level of the power output stage.

Abstract: An amplifier includes a differential amplifier stage, a voltage amplification stage and a power output stage. The bias level of the output stage is proportional to current through the voltage amplification stage. The voltage amplification stage includes a current mirror whereby controlled current through a first leg of the current mirror controls current through the remaining, second leg, which, in turn, determines the bias level of the power output stage. Control circuitry senses a parameter of the amplifier, such as DC bias or input signal level to generate a control signal which is applied to the first leg of the current mirror to thereby control bias level of the power output stage.

Abstract: A telephone control unit 12 allows the calling party to optionally select either a standard telephone call or a voice-mail transmission. If a voice-mail message is selected, the system allows the user to dictate the message which is then analog-to-digital converted and stored in memory. Once the user selects the receiving party's telephone number, the system dials the number and sends a header signal to the receiving unit indicating that a voice-mail transmission is desired. If the receiving unit detects the voice-mail header, it sends an acknowledgment signal, whereby the transmitting unit digitally compresses the stored voice-mail message and transmits the compressed message through the telephone network to the receiving site. The receiving site then flashes an indicator to the user that voice-mail is waiting. Upon a user replaying a voice-mail signal, the receiving site decompresses and digital to analog converts the signal for reproduction by the user.