| 摘要 |
A power amplifier has a signal input stage to which an input signal is applied to produce an input stage output. An input signal amplifier is connected to receive the input signal to produce an amplified input signal from an active device at an output of the input signal amplifier. A push-pull signal output stage has first and second transistors. The first transistor has a current path connected between a supply voltage and an output node, and the second transistor has a current path connected between a reference voltage and the output node. The amplifier output provides variable drive current directly to a base of the first transistor, thereby enabling increased drive current to be realized. The power amplifier also includes a common mode biasing circuit connected to bias the first and second transistors for class AB operation, and the input stage output provides a signal base drive current to the first transistor separate from the common mode biasing circuit. This further increases the drive current that can be supplied to the base of the first transistor. By virtue of the direct connection of the current path of the first transistor between the supply voltage and the output node, and its base connection to the output of the input signal amplifier, the voltage on the base of the first transistor is enabled to swing to within 1Vce SAT from the supply voltage. <IMAGE> |
