The class B PA has two parallel stages each of which conducts for only 180 degrees, thereby achieving a higher efficiency than class A PA. Class B requires that each transistor to turn off for half of the period (i.e conduction angle is 180 degrees). The gate bias voltage of the devices is therefore chosen approximately equal to their threshold voltage.

When M1 is on,Id1 flows from node X, producing a current in the secondary that flows into RL and generates a positive Vout.

When M2 is on and draws current from node Y, the secondary current flows out of RL and generates a negative Vout.

If the parasitic capacitances are small and the primary and secondary inductances are large, then Vx and Vy are also half-waved rectified sinusoids that swing around Vdd. The efficiency of the class B amplifier is calculated as 79%.