Bandgap Circuit Voltage Calibration via Resistor Ladder and Output Switch
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Solution Overview
Problem
Bandgap circuits in integrated circuits face inaccuracies due to variations in transistor threshold voltages, resistor ratios, and geometrical parameters, leading to unstable reference voltages and operation errors.
Innovation Solution
A bandgap circuit with a temperature-independent core and a resistor ladder that scales voltage levels, combined with an output switch for calibration, minimizes variations by generating a calibrated output voltage independent of process, power supply, and temperature variations, using a current mirror to provide a proportional-to-absolute-temperature current.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Temperature
If a bandgap circuit is used to generate temperature-independent voltage, then temperature stability is improved, but process variation and device parameter variation still cause output voltage inaccuracy
Solution Approach 1:
The circuit is divided into a bandgap core circuit that generates temperature-independent voltage and a separate calibration circuit that corrects process variations. The core circuit handles temperature compensation while the calibration circuit handles absolute voltage level accuracy, separating these two functions to resolve the contradiction.
Solution Approach 2:
A calibration circuit is implemented that measures the actual output voltage of the bandgap circuit and adjusts it through feedback to match a desired reference voltage level. This feedback mechanism compensates for process variations and device parameter differences, improving output voltage accuracy while maintaining temperature independence.
2Adaptability or versatility
If device parameters are varied due to different fabrication processes, then manufacturing flexibility is improved, but output voltage consistency deteriorates
Solution Approach 1:
The calibration circuit dynamically adjusts circuit parameters (such as resistor ratios or transistor operating points) to compensate for variations in device parameters caused by different fabrication processes. By changing these parameters through calibration, the circuit maintains consistent output voltage across various manufacturing conditions.
Solution Approach 2:
The calibration circuit performs preliminary adjustment of the output voltage during or after fabrication to account for process variations. This preliminary action ensures that despite differences in fabrication processes and resulting device parameters, the output voltage is pre-adjusted to the correct level before the circuit enters normal operation.
3Temperature
If reference voltage is derived from bandgap output, then temperature independence is improved, but reference voltage accuracy deteriorates due to bandgap output drift
Solution Approach 1:
The calibration circuit acts as an intermediary between the bandgap core circuit and the reference voltage output. It takes the temperature-independent voltage from the core circuit, measures its actual level, and adjusts it through the calibration mechanism to produce an accurate reference voltage, thus mediating between temperature independence and accuracy requirements.
Data Source
AI summary
A bandgap circuit generates a process and temperature independent voltage. The bandgap circuit includes a bandgap core that generates a temperature independent voltage. The bandgap circuit also includes a resistor ladder that is coupled in parallel to the bandgap core and scales the temperature independent voltage into voltage levels proportional to the temperature independent voltage. An output switch of the bandgap circuit connects the output of the bandgap circuit to one of the voltage level that is substantially equal to a desired voltage level. The bandgap circuit may also include a current mirror that outputs a proportional to absolute temperature current.