| 摘要 |
Parallel primary winding sections 30a,30b of a step-up balun transformer in the output circuit of a transmitter amplifier are selectively put into circuit by switches 62-68 so that the real part of the load impedance presented to the amplifier, and hence the output power transmitted by the antenna, may be adjusted. The primary winding sections may comprise single loops fabricated, without vias, in a single thick top metal layer (figure 5) affording low electromigration. The primary winding sections couple to the secondary winding with different coupling factors k. The secondary winding 32 may comprise two turns that are disposed closely adjacent the inner and outer sides of primary loop 30b to increase the coupling factor between windings 32 and 30b. The switches 62-68 may be implemented by use of cascode devices within the amplifier. The technique allows adjustment of transmitted power without a requirement for variation of the power supply. |
