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Electronics and Noise, Ch. 14 and 16, Senturia

Electronics and Noise, Ch. 14 and 16, Senturia. What determines the performance of a sensor? Minimum Detectable Signal? (What does this mean?) Precision? Accuracy? Frequency Response? Dynamic Range? (What does this mean?). Look at the ADXL 204. Sensitivity What is the significance?

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Electronics and Noise, Ch. 14 and 16, Senturia

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  1. Electronics and Noise, Ch. 14 and 16, Senturia • What determines the performance of a sensor? • Minimum Detectable Signal? (What does this mean?) • Precision? • Accuracy? • Frequency Response? • Dynamic Range? (What does this mean?)

  2. Look at the ADXL 204 • Sensitivity • What is the significance? • Noise Specs? • What is the signficance? • Anything on accuracy or precision? • ?

  3. Plan • Start with elecronics – review op-amp circuits • Talk about noise in general • Do some examples using specs for particular op-amps.

  4. Slew-Rate • Another limitation, in addition to all the others, that comes from properties of the op-amp circuit: • Slew-Rate: • The rate at which the output voltage can change • Typically measured in V/ms (at the output) • It is another spec. for op-amps • Typically 0.5-1,000 V/ms • Sometimes this needs to be large for driving something like an electrostatic actuator.

  5. Noise, Ch. 16, Senturia • Noise often limits performance of MEMS sensors and other devices (oscillators, filters, for example). • What we often think of as noise can be divided into 2 (or more) parts. • 1. Interference. • 2. Random noise. • 3. Drift, aging effects… (random noise??)

  6. Interference • Definintion: Unwanted sensitivity to external or internal disturbances. • Electrical, thermal, mechanical, optical… • Examples. • Electrical: Capacitive coupling to 60 Hz, radio waves, driving voltage to output … • Mechanical: Sensitivity to vibration… • Optical: Sensitivity to ambient light. • Thermal: Sensitivity to temperature (very common!) • System design critical (Senturia has examples) • References: Keithley, Low-Level measurements + others.

  7. Random Noise • Thermal noise. • Dissipative processes result in fluctuations. • Energy storage elements have a non-zero fluctuating amount of energy stored. • Shot noise. • Current consists of discrete particles. • Flicker noise (1/f noise). • Mostly capture and release of carriers from traps in electrical circuits. Many physical mechanisms, generally.

  8. Thermal Noise • Statistical mechanics -> average energy of a particle = 3/2 kBT. (1/2 KBT for each degree of freedom (x, y, z)) • Mass with 1 degree of freedom -> ½ kBT <-> inductor! • Inductor has on average ½ kBT of energy. • The capacitor is also an energy storage element with one degree of freedom. If connected to its environment with a resistor (or almost anything else) it has an average stored energy of ½ kBT! This does not depend on the size of the resistor or capacitor! • Spring (capacitor) also has ½ kBT. • This is characteristic of thermal noise.

  9. 4kT=4.1x10-21 at 300 K

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