Internal Reference Voltage Droop under External Analog Loading
External analog load currents extract direct current and charge pulses from internal bandgap reference nodes, inducing static droop and transient conversion errors.
Internal Voltage Reference
Potential Source
Stable voltage generation is the foundation of high-resolution analog conversion and sensor bias networks. An internal voltage reference provides a constant, known electrical potential within a larger integrated circuit. This built-in source is designed to remain constant despite fluctuations in supply voltage or operating temperature.
Bandgap Design
Silicon bandgap circuits operate by summing a voltage that has a negative temperature coefficient with one that has a positive temperature coefficient. This addition produces a stable voltage of approximately one point two volts, which is nearly independent of temperature changes. An integrated internal voltage reference uses this principle to achieve stability over wide temperature ranges.
The performance is further enhanced by trimming the resistors during manufacturing using laser correction.
Temperature Coefficient
Drift with temperature is measured in parts per million per degree Celsius and indicates the reference’s thermal stability. If an internal voltage reference has a coefficient of ten parts per million, a seventy-degree temperature change causes a zero point zero seven percent shift in output voltage. This change directly impacts the accuracy of the overall system by shifting the full-scale range of the converter.
Precise thermal calibration is required to correct for this drift in software when the system operates across extreme temperature spans.
System Integration
Noise and output impedance limit the performance of these circuits when driving capacitive loads. High frequency noise is filtered out by adding external bypass capacitors to the reference pin. However, some references become unstable when presented with excessive capacitance, necessitating a series isolation resistor to maintain loop stability.
Selecting the correct bypass configuration is a critical step in circuit integration to prevent oscillations that would otherwise degrade the resolution of the analog-to-digital converter.