Essay Example on Integrated sensors are in demand these Days








Introduction Integrated sensors are in demand these days The will for simultaneous achievement of highly energy efficient high resolution as well as better stability in long term devices which will reduce noise affecting frequency reference s jitter as well as energy budget These all contribute to a smart temperature sensor CMOS based temperature sensors are much more efficient than BJT based sensors due to its higher resolution and better figure of merit Temperature coefficient plays a crucial role in resistor based temperature sensors as it is used to determine its resolution and energy efficiency A type of resistors such as poly and diffusion based were also used but their resolution was limited due to thermal noise of the read out electronics From research point of view researchers tried to innovate sensors based on a thermistor embedded Wien bridge RC filter which is an energy efficient and has high resolution as well as better stability

With the help of this technology a resolution of about 410uK can be achieved in 5 ms conversion time and a figure of merit up to 0 13pJ K 2 2 Characteristics CMOS resistors There are many type of resistors available with different characteristics such Metal based which can have large temperature coefficient moderate 2nd order tc and has very small sheet resistance as well as small stress sensitivity Due to low resistance the power consumption is very high as well as area also increases Diffusion type CMOS resistors possess moderate temperature coefficient as well as moderate 2nd order tc But it has large sheet resistance and moderate supply dependency Its resistance also depends on doping level and reverse biased voltage between them and substrate Resistors like silicide poly and silicide diffusion whose characteristics lies between metal and silicon thus forms a metal silicon alloy which is highly conductive and are more linear temperature dependant it contains properties such as much lower resistance have low temperature dependent and less stress sensitivity which makes it quite stable even up to 500 degC We can see that silicide resistor are the best compatible resistors for CMOS processes which can integrated to high performance temperature sensors The silicided poly resistor can be used as main sensing element due to low temperature dependent For reference impedance Wien Bridge RC filter which contains MIM capacitors are much suitable due to nearly zero TC

It is an energy efficiency model based on synchronous demodulation can be used to estimate achievable temperature sensing resolution Noise somehow can be reduced easily Design and implementation Wien Bridge circuitry can be driven by complementary square wave instead of sine waves to reduce energy consumption To digitize the output of WB s current a continuous time PHASE DOMAIN DELTA SIGMA MODULATOR is used which will also responsible for high resolution PCD SM Packaging and Challenges Plastic packaging is preferred due to low cost as compared to the ceramic packaging Mechanical stress affects the sensor s accuracy but due to metal like properties it exhibits stress sensitivity of silicided poly resistor as compared to that of non silicided poly resistor The maximum accuracy it can achieve is about or 2 deg C Conclusion As compared to other sensors the s p poly sensor it can achieve energy efficiency of 0 13pJ K 2 which might be 5 times better than the state of the art of CMOS SENSORS It can achieve an inaccuracy of or 3deg C when it will be packaged in ceramic packaging It s in accuracy can be comparable to BJT based sensors Based on WB RC filter a resistor based smart sensor can be implemented in a standard 0 18uM CMOS technology for the temperature compensation of MEMS quartz frequency references whose output phase can be digitized using continuous time PHASE DOMAIN DELTA SIGMA MODULATOR 

Due to high temperature coefficient and low noise of silicided poly resistor the sensor can achieve up to 400uk resolution in a 5ms conversion time and a resolution figure of merit of 0 13 pJK 2 Acknowledgement I would like to thank Dr Ramesh Vaddi and P hd Scholar Mr Aditya Japa for their valuable assistance and support in reviewing this topic References 2 M H Perrott et al A temperature to digital converter for a MEMSbased programmable oscillator with 0 5 ppm frequency stability and 1 ps integrated jitter IEEE J Solid State Circuits vol 48 no 1 pp 276 291 Jan 2013 1 M Shahmohammadi K Souri and K A A Makinwa A resistor based temperature sensor for MEMS frequency references in Proc ESSCIRC Sep 2013 pp 225 228 2 P Park D Ruffieux and K A A Makinwa A thermistor based temperature sensor for a real time clock with 2 ppm frequency stability IEEE J Solid State Circuits vol 50 no 7 pp 1571 1580 Jul 2015 Resistor Based Temperature Sensor With 4 a 0 13 pJ K2 Resolution FoM

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