Bandgap Current Output Calibration Using Shared On-Chip ADC
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Solution Overview
Problem
Existing bandgap generators with multiple adjustable outputs face challenges in precise calibration due to process variation and mismatch, which are costly and inefficient when using external automated test equipment (ATE) for individual calibration.
Innovation Solution
A method and circuit that calibrate a first adjustable output using external ATE and then utilize on-chip switches to couple other adjustable outputs to an analog-to-digital converter (ADC) for measurement and calibration, allowing for precise matching of current levels without increasing ATE costs or adding output pins.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If external ATE is used to calibrate each adjustable output individually, then calibration precision is improved, but cost and complexity increase
Solution Approach 1:
An on-chip ADC is introduced as an intermediary device to measure the output currents of multiple adjustable outputs. Instead of using external ATE for each output, the ADC serves as an on-chip measurement intermediary that captures current values, enabling precise calibration without requiring multiple external test equipment connections.
Solution Approach 2:
The ADC is designed to serve multiple functions: it measures the calibrated reference output current, measures other adjustable output currents for comparison, and provides digital signals for calibration code generation. This multi-functionality allows a single device to replace multiple ATE connections, reducing system complexity while maintaining calibration precision.
2Measurement precision
If multiple output pins are added for individual calibration, then calibration accuracy is improved, but chip complexity and cost increase
Solution Approach 1:
Multiple calibration measurement functions are merged into a single ADC device on the chip. Instead of having separate output pins for each adjustable output to connect to external ATE, the patent combines all measurement functions through the shared ADC, which is controlled by a calibration controller to sequentially measure different outputs through switching circuitry.
Solution Approach 2:
The ADC acts as an on-chip intermediary that eliminates the need for multiple external test connections. By routing multiple adjustable outputs through switching circuitry to the single ADC, the system achieves individual calibration capability without adding multiple output pins to the chip package.
3Ease of manufacture
If process variation and mismatch are not compensated, then manufacturing simplicity is maintained, but output precision deteriorates
Solution Approach 1:
A feedback mechanism is implemented where the ADC measures the actual output current of each adjustable output, compares it with the target value, and the calibration controller adjusts the calibration code accordingly. This closed-loop feedback compensates for process variation and transistor mismatch, achieving high output precision without complicating the manufacturing process.
Solution Approach 2:
The calibration code, which is a digital parameter, is adjusted to change the output current characteristics of the adjustable outputs. By modifying this parameter based on ADC measurements, the system compensates for process variations and mismatch, achieving precise output currents while maintaining manufacturing simplicity.
Data Source
AI summary
A method and an apparatus to provide bandgap calibration for multiple outputs are disclosed. In one implementation, a computing chip includes a bandgap current generator; a first adjustable current output coupled to the bandgap current generator; a second adjustable current output coupled to the bandgap current generator; a first switch selectively coupling the first adjustable current output to a calibration circuit and to a first analog-to-digital converter (ADC); and a second switch selectively coupling the second adjustable current output to a load on the computing chip and to the ADC.