Single-Ended Analog Architecture

The singled-ended analog architecture comprises a temperature sensor on the bulk chip, three single-ended analog proportional microhotplate temperature controllers 

A micrograph of the single-ended hotplate-based microsystem is shown in Fig. 6.2 and features a die size of 5.0 x 2.9 mm. This system is a minimal implementation of a temperature-controlled microhotplate system. Temperature modulation is facilitated by an direct access to the input voltage A modulation of the input voltage is translated into a modulation of the microhotplate temperature. Another interesting application of the system includes its use as a microcalorimeter or as a material research platform [145]. The schematic of the temperature-control loop is shown in Fig. 6.3. 

The temperature sensor is located in the microhotplate center (J2x, 10 kO nominal). This polysilicon resistor is biased with a temperature-independent current source (/bias)- The voltage-drop across the polysilicon temperature sensor provides the feedback signal for the temperature controller. 

The dominant pole of this temperature control system is determined by the thermal time constant of the microhotplate, which is approximately 20 ms. The open-loop gain of the single-ended analog architecture (Aol seaa) i given by Eq. (6.1)  

The performance of the single-ended analog proportional temperature controller in the tracking mode is shown in Fig. 6.4. The measurement was done at room temperature, and the control voltage of microhotplate 1 was increased in steps of 100 mV. For example, a control voltage of 1.60 V produced a microhotplate temperature of approximately 355 °C. Microhotplate 2 was kept at a constant temperature of 200 °C and microhotplate 3 was kept at 350 °C. 

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Fig. 6.1. Block diagram of the single-ended analog architecture...

Fig. 6.6. Discrepancy between ambient temperature and bulk-chip temperature as a function of the microhotplate temperature for the single-ended analog architecture (DIE package)...

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