For the purpose of multiband mobile phone power amplifier (PA) design, the prospect of using a distributed amplifier (DA) has been investigated, which over the last 50 years is well known for its excellent broadband behaviour. In order to better adapt the DA to mobile phone PA applications, a new concept is proposed, namely the linear diplexing tapered DA. To verify this concept, the following designs have been investigated:
- Single stage PCB demonstrator.
- Two-stage on-chip design, which has tapered DA as driver and the diplexing tapered DA as a final PA stage.
Due to the unique properties of the (diplexing tapered) DA, some commonly used techniques in single ended PA designs are not applicable. Therefore modifications and adaptations are made. Furthermore, the supplementary properties of the diplexing tapered DA are discussed:
- Stage bypass for PAE enhancement of DA during large back-off (BO) operation.
- Due to multiple feedback loops and nonlinear devices, large signal and parametric stability are characterised by system identification method.
- Due to the inferior linearity of DA, a special dynamic biasing circuit to compensate for the gain expansion is proposed.
- The ability to apply spectrum aggregation and load balancing techniques.