Current consumption benefit of adjustable bias in low-power mode of WCDMA power amplifiers

The effect of an adjustable bias circuit on current consumption is shown in this paper, comparing four variants of a WCDMA power amplifier. All variants are designed to operate in the WCDMA band 5 (824–849 MHz) and include a high-power and a low-power mode for two different output power ranges. The variants are identical in the high-power mode, but differ in their low-power mode biasing. They are designed with permutations between conservative (high) and aggressive (low) mirror currents, as well as a fixed bias and an adjustable bias. All four circuits switch between high-power and low-power mode and are measured with lowering the collector voltage at lower output power using a DC-DC converter. The influence of the adjustable bias on RF performance is detailed and it is proven that the chosen adjustable bias does not deteriorate circuit behaviour. Furthermore, the current consumption is compared among all four variants using DG.09 current metric. The lowest DG.09 current is achieved with the variant having small mirror currents and the adjustable bias circuit.