Temperature Control Loop and Sensor Resistance Readout

3 Temperature Control Loop and Sensor Resistance Readout 

The MOSFET heater is directly driven with this bit stream or optionally, the bit stream can be routed through a low pass filter. Early experiments revealed that driving the heater transistor with the raw bit stream might cause some electromigration due to the large peak currents that occur. The low-pass filter was therefore included to avoid such current peaks in order to enhance the device stability and life time. 

As the thermal capacitance and resistance of the hotplate provide a thermal low-pass transfer function (with the dominant pole corresponding to a characteristic time of 10-20 ms, depending on the fabrication process), the ZA modulator driving the hotplate constitutes a linear noise-shaping DAC with an output in the thermal domain. 

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