Class ab amplifier with bias control

An amplifier arrangement comprising:

• a first power amplifier (T1) having a drain connected to a positive drive voltage and a gate connected to an input signal,
• a second power amplifier (T2) having a drain connected to a negative drive voltage and a gate connected to said input signal,
• wherein a source of the first power amplifier and a source of the second power amplifier are both connected to a load (RL),
• a first current sensor (1) detecting a first drain current from said first power amplifier,
• a second current sensor (2) detecting a second drain current from said second power amplifier,
• processing circuitry (3) adapted to identify an idle current as the smallest drain current of said first and second drain currents,
• a comparator (4) for comparing said idle current with a pre-set idle current set point, to provide an error signal,
• a bias control loop (5) providing a feedback signal based on said error signal, and
• means for driving a bias current dependent on said feedback signal through a resistor connected between the input signal and the gate of an inactive one of said first and second power amplifiers, so as to ensure that a drain current from said inactive power amplifier is equal to said pre-set idle current.