Bandgap Voltage Reference Using Single Diode PTAT Generation
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Solution Overview
Problem
Conventional bandgap voltage references are sensitive to package shifts due to pressure from the package, which affects the accuracy of the voltage reference by introducing shifts in both Vbe and PTAT voltage, leading to instability in temperature and power supply variations.
Innovation Solution
A bandgap voltage reference is designed using a single diode biased at two different current levels at different times, eliminating the absolute value of Vbe and any package shift in the PTAT voltage, implemented in either single or differential circuit topologies, and optionally includes curvature correction to further stabilize the voltage reference.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional bandgap voltage reference designs use two diodes biased at different current densities to generate PTAT voltage, then the reference voltage can be generated, but the circuit becomes sensitive to package shift due to piezoelectric effects
Solution Approach 1:
The patent merges the function of two separate diodes into a single diode that is sequentially biased at two different current densities. The same physical diode structure performs both measurement functions, eliminating the package shift sensitivity that arises from using two separate diodes with potentially different mechanical stress states.
Solution Approach 2:
The patent introduces dynamic switching between two bias conditions for a single diode. A switch mechanism dynamically connects the diode to different current sources at different times, allowing the system to measure both voltage levels using the same diode under different operating conditions, thereby eliminating static package shift effects.
2Power
If pressure from the package introduces piezoelectric effect on the integrated circuit die, then Vbe and PTAT voltage are shifted, but the PTAT voltage gain is increased by a factor of 5-20 making it more sensitive to package shift
Solution Approach 1:
The patent combines the PTAT voltage generation function into a single diode measurement process. By measuring the voltage across one diode at two different current densities and computing the difference, the system maintains high PTAT voltage gain while eliminating the differential package shift sensitivity that plagues two-diode implementations.
Solution Approach 2:
The patent creates a temporal copy of the measurement process by sequentially applying two different current densities to the same diode. This allows the system to obtain both measurement values from identical physical conditions, effectively canceling out package shift effects while maintaining the necessary voltage gain for accurate reference generation.
3Object-affected harmful factors
If a single diode is used to generate PTAT voltage by biasing at two different current levels at different times, then package shift sensitivity is eliminated, but the circuit requires switching mechanisms
Solution Approach 1:
The patent employs dynamic switching to simplify the overall circuit architecture. By using switches to dynamically connect a single diode to different current sources at different times, the system achieves package shift immunity while the switching complexity is managed through systematic clocking and control logic.
Solution Approach 2:
The patent implements periodic switching between two bias conditions for the single diode. The switching operates in a regular alternating pattern, allowing the system to sequentially measure both voltage levels and compute the PTAT voltage through periodic sampling, which simplifies the control logic compared to simultaneous multi-diode measurements.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This approach significantly reduces package shift sensitivity, enabling precise and stable reference voltage generation applicable to both single-ended and differential implementations, while allowing for standard manufacturing processes and packaging, thus lowering product costs and enhancing flexibility.
Implementation Method 1
a proportional to absolute temperature (PTAT) voltage is generated using a single diode biased at two different current levels at two different times
Implementation Method 2
Pressure from the package (e.g., a plastic package) can introduce a piezoelectric effect on the integrated circuit die that can shift Vbe and PTAT voltage (ΔVbe)
Data Source
AI summary
In a bandgap voltage reference with low package shift, a proportional to absolute temperature (PTAT) voltage is generated using a single diode biased at two different current levels at two different times. Using the same diode for both current density measurements removes the absolute value of the base-emitter junction voltage (Vbe) and any package shift in the PTAT voltage. The bandgap voltage reference can be implemented in a single or differential circuit topology. In some implementations, the bandgap voltage reference can include circuitry for curvature correction.