| 摘要 |
<p>This tuneable amplifier uses a MOSFET tetrode, i.e. two field-effect transistors with common source and drain electrodes, and can be operated using a single d.c. supply. The amplifier input (5) is fed by an antenna installation (6). The required frequency is selected by a resonant circuit (4) and fed to the gate or the first FET (A) via a de-coupling capacitor (3). This gate is biased by a resistive divider (7,8). The source electrode is biased by a resistive divider (10,11) and a coupling capacitor (9). The gate of the second FET (B) is connected, via a resistor (12), to an external regulating-signal generator (14) which is controlled by feedback from the amplifier output (18). The drain electrode is fed via another resonant circuit (16) and a de-coupling capacitor (17) to the output (18) of the amplifier. The use of a single semi-conductor and a single d.c. supply reduces the cost of this amplifier compared with conventional circuits.</p> |
