Gemini South is replacing one of the (3) CILAS DMs with a 349-actuator Xinetics DM in its GeMS MCAO system. Xinetics mirrors operate over a 40-100V dynamic range and require that inter-actuator stroke differences are limited to half-scale; each actuator must be within 30V of its neighbor to prevent mechanical stress and possible face sheet separation. A robust way to implement this protection is to use high power transient voltage suppressors (TVSs) as a 2D-mesh between the amplifiers and mirror, but this has system implications. A sustained clamp condition dissipates significant power in the devices, and if an actuator fails as short (which occurred once with the DM in a thermal chamber), the system is subject to a cascade failure event as multiple outputs drive the shorted actuator through the TVS network. This latter risk is readily resolved by using series fuses to the DM. In this third-generation driver, current sensing and logic inhibit amplifier outputs after a sustained TVS clamp condition or shorted output, and LED indicators show the location. Redundant thermal sensing is used on modular TVS row and column boards. A second 2D-mesh of high impedance resistors after the fuses will hold an unpowered channel to the average voltage of its neighbors, with a negligible influence function. A Failure Modes and Effects Analysis shows significant fault tolerance.
Full-custom electronics have been designed to drive Xinetics deformable mirrors, for use with the PYRAMIR (Calar Alto) and LINC/NIRVANA (Large Binocular Telescope) AO instruments, under contract to the Max-Planck-Institut fur Astronomie (MPIA). Significant enhancements to the original 1998 design for ALFA (Calar Alto) have been incorporated, including an embedded 2.1 Gb/s fiber link, temperature-controlled bias voltage, and multiple tip-tilt control outputs. Each 7U chassis with integral power supplies can drive mirrors of up to 349 actuators, and may be cascaded to support larger mirrors. A customized 600 MHz 'C6415 DSP module was specified to minimize latency, with frame rates above 7.5 KHz demonstrated for the 349-actuator DM. Power op-amps with 0.38 W/channel quiescent dissipation were chosen to reduce heat load, while supporting full-power (60 Vpp) bandwidth to above 300 Hz. These subsystems were successfully integrated in Heidelberg during November, 2003. The engineering firm responsible for the design, Cambridge Innovations, has since been awarded two additional contracts for DM electronics, including a new full-custom design for AURA (Gemini Observatory) to drive multiple high-voltage CILAS piezo bimorph DMs.