Adaptive class AB amplifier for TDMA wireless communications systems

In a mobile portable handset unit in a TDM/TDMA digital telephony system which transmits an RF (radio frequency) burst signal at an uplink frequency during an assigned time-slot within a frame to a fixed port within the system and does not transmit during the period within the frame outside the assigned time-slot, adaptive apparatus for amplifying a modulated RF burst input signal to a power level for transmission, the adaptive apparatus comprising:

• class AB amplifier means comprising at least one FET for amplifying the modulated RF burst input signal;
• measuring means for measuring the drain current of said at least one FET of said class AB amplifier means during the period within a frame that is outside the assigned time-slot of the burst;
• comparing means for comparing the drain current measured during the period within a frame outside the assigned time-slot of the burst with a reference quiescent drain current value that keeps the amplifier slightly "on";
• and
• adjusting means for adjusting the drain current of said at least one FET of said class AB amplifier means during the period within a frame outside the assigned time-slot of the burst so that it moves toward the reference quiescent drain current value.

In a mobile portable handset unit in a TDM/TDMA digital telephony system which transmits an RF (radio frequency) burst signal at an uplink frequency during an assigned time-slot within a frame to a fixed port within the system and does not transmit during the period within the frame outside the assigned time-slot, a method for adjusting the bias of a class AB amplifier in the handset unit which amplifies a modulated RF burst input signal to a power level for transmission and which comprises at least one FET, the method comprising the steps of:

• measuring the drain current of the at least one FET of the class AB amplifier during the period within a frame that is outside the assigned time-slot of the burst;
• comparing the drain current measured during the period within a frame outside the assigned time-slot of the burst with a reference quiescent drain current value that keeps the amplifier slightly "on";
• and
• adjusting the drain current of the at least one FET of the class AB amplifier during the period within a frame outside the assigned time-slot of the burst so that it moves toward the reference quiescent drain current value.