Voltage Reference Circuits
A voltage reference is an electronic device which produces a constant voltage regardless of the loading on the device, temperature changes, passage of time and power supply variations.
The voltage reference circuit most commonly used in integrated circuits is the bandgap voltage reference.
A bandgap voltage reference uses analog circuits in order to add a multiple of the voltage difference between two bipolar junctions biased at different current densities to the voltage developed across a diode.
The diode voltage has a negative temperature coefficient and the junction voltage difference has a positive temperature coefficient. When added in the proportion which is required in order to make these coefficients cancel each other, the resultant constant value is a voltage which is equal to the bandgap voltage of the semiconductor.
Types of Voltage References:
- There are several different kinds of voltage references. Most common types categorized by type, tolerance, rated voltage, reference voltage, forward (drive) current, rated current, quiescent current and packaging type. The most common sizes for tolerance are ± 2%, ± 1% and ± 0.5%.
- Voltage references have a major impact on the performance and accuracy of analog systems.
- A 5 mV tolerance on a 5 V reference corresponds to 0.1% absolute accuracy which is only 10-bit accuracy.
- For a 12-bit system, choosing a reference that has a 1 mV tolerance may be far more cost effective than performing manual calibration, while both high initial accuracy and calibration will be necessary in a system making absolute 16-bit measurements
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