| 摘要 |
<p>A high-efficiency amplifier of the class-G type comprises a first transistor (T1), whose collector is connected to a first supply voltage (V1) via a first diode (D1), and a second transistor (T2), which is connected in series with said first transistor and which has its collector connected to a second supply voltage (V2). The first transistor (T1) is driven via a third transistor (T3), which is arranged as an emitter follower by means of a first current source (5), the input voltage (Vi) being applied to this third transistor. For a low input voltage (Vi) the second transistor (T2) is cut off and the first transistor (T1) is connected to the first supply voltage (V1) via the first diode (D1). Above a specific inputvoltage (Vi) the second transistor (T2) is driven into conduction by means of a driver circuit, so that the first transistor (T1) is connected to the second supply voltage (V2). This driver circuit comprises a first current path which is arranged between the second supply voltage (V2) and the emitter of the third transistor (T3) and which comprises the series arrangement of a second current source (7), the emitter-collector path of a fourth transistor (T5) and a second diode (D4), and a second current path which is arranged between the junction point (3) between the first transistor and the second transistor (T1, T2) and the common point (11) and which comprises the series arrangement of a third diode (D3), a fourth diode (D4) and a third current source (8). The base of the fourth transistor (T4) is connected to the junction point (9) between the third diode and the fourth diode (D2, D3) and the collector of the fourth transistor (T5) is connected to the third current source (8) by means of a fifth diode (D5). By means of such a driver circuit it is possible to drive the outpur (2) to the value of the second supply voltage (V2) minus substantially one base-emitter voltage. </p> |
