Power Budget per Reading across Competing Sensing Principles
Sensing power budgets depend on physical excitation energy, analog settling delays, and converter sampling overhead across operating duty cycles.
Temperature Leakage Current
Parasitic Conduction
Unwanted current flow through insulating materials increases as the temperature of a semiconductor or dielectric rises. Temperature leakage current occurs when thermal energy allows electrons to cross barriers that are normally non conductive, such as a reverse biased diode junction or a capacitor oxide layer. This phenomenon is a primary cause of error in high impedance measurement circuits.
Exponential Growth
The magnitude of the stray current typically doubles for every 10 degree Celsius increase in the environment. At room temperature, the temperature leakage current of a modern MOSFET might be in the picoamp range. When the device reaches 125 degrees, the current can rise to microamps and interfere with the logic state.
Guarding Technique
High precision board layouts use guard rings to divert these stray currents away from the sensitive input pins of an operational amplifier. By surrounding the input trace with a low impedance path at the same potential, the temperature leakage current is intercepted before it reaches the signal. This is necessary in applications like pH sensors or gas detectors where the source current is extremely low.
Humidity often compounds the effect by creating conductive paths on the surface of the PCB.
Material Selection
Teflon or specialized ceramics are used in extreme environments to provide higher insulation resistance. Choosing materials with a wide bandgap reduces the temperature leakage current at high operating points.