Band-Gap Voltage Reference Diode [Temperature Compensated Circuit] 

How does a Band-gap voltage reference diode work? What is the value of output voltage? What should be the choice of circuit components to ensure near zero temperature coefficient for this reference diode so that generated output voltage doesn't change with temperature? These questions are discussed and answered in this bandgap reference voltage design example and tutorial. There are many practical applications for Band-gap circuits that are effectively Zener diodes with practically zero temperature coefficient. Example application is stable reference voltage in chip design including the wireless transceiver chips in cell phones. The example band-gap circuit discussed in this video is implemented with five NPN BJT and one PNP bipolar junction transistors. Three of the NPN BJT transistors are required to be matched transistors (sharing the same process, junction and thermal properties) in order to have the same saturation current (Is) and same thermal voltage (VT) which is roughly 26mV when PN junction is at 300 kelvin room temperature. Using a combination of KVL and Shockley equation of PN junction of BJT transistor, it is proven that the output generated voltage of this reference diode is 1.28V with near zero thermal sensitivity. Analog Devices LM313 from Texas Instruments REF54 0.8ppm/°C drift precision voltage reference are examples of voltage references that can be purchased from circuit component suppliers Digikey or Mouser. At the end of this video, an example of component selection for the value of resistors is provided.

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