The GAIA digital board developed by INAF was designed to bias up to ten stages of cryogenic low noise amplifiers (LNAs) and to deliver a maximum drain current Idmax50 mA with a drain voltage Vdmax5 V for each of them. The GAIA board monitors and controls each of the stages independently. However, such board cannot be employed to monitor and control the AETHRA WP1 75-116 GHz downconverter module as the power amplifiers of the fully-integrated MMIC developed at IAF, integrated into the downconverter module, require current values of up to 300 mA each, that is six times greater than what GAIA can deliver. Therefore, a power stage of the GAIA board has to be developed to comply with the high-current bias requirements of the AETHRA WP1 downconverter. Here, we describe the design of the power stage of the GAIA board, named PSG (Power Stage Gaia). The PSG is a four-layer digital bias board, to be connected in series with GAIA, capable of delivering up to 10 × high-current stages. One GAIA board is used to monitor and control one PSG board. The latter is an extension of GAIA and cannot be used independently of it. Therefore, one GAIA board plus one PSG board must be used in conjunction to monitor and control up to 10 high-current stages of the AETHRA WP1 downconverter. The version 1.2 of the GAIA board, developed for biasing, monitoring and controlling of the LNAs, cannot be used in conjunction with the PSG but requires a small modification to allow data interchange between the two boards. A new GAIA board, version 1.5, must be used in conjunction with the PSG. This document describes the main specifications of the GAIA bias board version 1.2, the requirements and design of the PSG as well as the upgraded GAIA version 1.5. In Section 1 we summarize the specifications of the GAIA board, version 1.2 (current version). The PSG is described in Section 2, while Section 3 reports on the upgrade of the GAIA board (version 1.5) for use with the PSG.