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CMOS design of Digital to Analog converters for active matrix Spatial Light Modulator applications

: Paramesh, Vidwath
: Presberger, Thomas; Horstmann, John Thomas

Chemnitz, 2018, IX, 65 S., 6 S. Anhang
Chemnitz, TU, Master Thesis, 2018
Master Thesis
Fraunhofer IPMS ()

Spatial light modulators (SLM) are devices that manipulate light with respect to the application. They consist of several micro mirrors that are deflected with respect to digital signals or analog voltages using certain Application Specific Integrated Circuits (ASIC). These micro mirrors are arranged in the form of a matrix. For the SLM reference taken for this thesis, an analog voltage is necessary for the deflection of micro mirrors. High voltage transistors are used to write voltages to a storage capacitor which in turn deflects the micro mirror. With constantly flowing digital inputs to the ASIC, a Digital to Analog Converter (DAC) constitutes an important part it. To obtain the analog voltages, a DAC is designed as a part of this thesis with high efficiency in terms of power, area and resolution for low voltage applications. In addition to this, the high voltage transistors constitute a certain capacitance at its columns which needs to be driven by this DAC. Initially, a high speed, low power consumption class AB operational amplifier is designed to drive the capacitive load. Using this amplifier, four different DAC topologies are implemented. The best results with respect to the specifications given were obtained for the charge scaling sub DAC technique. Capacitors with a size as low as 200fF were used in the DAC owing to the implementation of the high speed operational amplifier, eventually saving up substantial area. A low error output voltage, with a settling time lesser than 500ns for the maximum voltages and a power consumption of only 109μW for individual columns of the SLM is obtained.