Bandgap Reference Circuit Trimming Sheet Resistance
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Solution Overview
Problem
Bandgap reference circuits face challenges in generating temperature-independent reference voltages due to variations in sheet resistance of resistors, requiring both high-temperature and low-temperature trimming, which increases digital overhead and affects accuracy.
Innovation Solution
A bandgap reference generation circuit that generates a trimmed PTAT current component independent of sheet resistance variations, using an additional PTAT loop to produce a current component invariant of process variations, which is then combined with a CTAT current component to generate a temperature-independent reference voltage.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If traditional bandgap reference circuit uses standard PTAT current generation with sheet resistance dependent resistors, then circuit complexity is reduced, but reference voltage accuracy deteriorates due to process variations and temperature drift
Solution Approach 1:
The PTAT current generation is segmented into two independent paths: one for generating the basic PTAT current and another for generating the trimmed PTAT current. The trimmed PTAT current path includes additional circuitry (current mirror, resistor ratio circuit) that is specifically designed to compensate for process variations, while the main path remains simple. This segmentation allows the complex compensation mechanism to be isolated and optimized without increasing the overall circuit complexity unnecessarily.
Solution Approach 2:
A trimmed PTAT current is introduced as an intermediary element that mediates between the basic PTAT current and the final reference voltage generation. This trimmed current serves as a compensation mechanism that cancels out the effects of sheet resistance variations and temperature drift, thereby improving reference voltage accuracy without requiring direct modification of the entire circuit architecture.
2Reliability
If trimming is performed at both high temperature and low temperature to compensate for process variations, then reference voltage accuracy across temperature range is improved, but digital overhead and processing time increase
Solution Approach 1:
The trimming is performed preliminarily during the manufacturing process rather than requiring real-time digital adjustment during operation. The trimmed PTAT current is designed to inherently compensate for process variations across the temperature range, eliminating the need for complex digital trimming algorithms and reducing processing time while maintaining reliability.
Solution Approach 2:
The invention changes the parameter of the PTAT current by introducing a trimmed version with a different temperature coefficient. This parameter change allows the current to compensate for process variations without requiring active digital control, thereby reducing digital overhead while maintaining temperature independence.
3Manufacturing precision
If sheet resistance of resistors is reduced to minimize process variations, then manufacturing precision is improved, but resistor area and consequently circuit area increase
Solution Approach 1:
Instead of using a single large resistor with tightly controlled sheet resistance, the invention uses a copying approach where a smaller resistor is replicated multiple times in series. This allows the use of standard sheet resistance values while achieving the required precision through the multiplication of smaller, more manageable resistor units, thereby reducing the overall area requirement.
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 minimizes drift in reference voltage, improving temperature accuracy and reducing the need for costly trimming at multiple temperatures, resulting in a more accurate and efficient bandgap reference generation.
Implementation Method 1
a first proportional to absolute temperature (PTAT) current generation section comprising a PTAT resistor and a current mirror circuit for generating a PTAT current component
Implementation Method 2
The CTAT current generation section includes a diode on which the trimmed PTAT current component is fed to generate a CTAT current component
Data Source
AI summary
A bandgap reference generation circuit in an integrated circuit (IC) and method for generating a bandgap reference voltage are disclosed. The bandgap reference generation circuit includes a first proportional to absolute temperature (PTAT) current generation section for generating a PTAT current component, a current circuit configured to generate a trimmed PTAT current component substantially invariant of sheet resistance of at least one resistor in the current circuit, and a complementary to absolute temperature (CTAT) current generation section including a diode on which the trimmed PTAT current component is fed to generate a CTAT current component. A combination of the PTAT and CTAT current components generate the bandgap reference voltage.