No-Trim LDO Voltage Regulator Using Bipolar Bandgap Layout
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Solution Overview
Problem
Traditional voltage regulator designs require trimming to address inaccuracies in bandgap voltage, which is costly, time-consuming, and prone to heat-related errors, necessitating the elimination of trimming and improvement of bandgap voltage accuracy.
Innovation Solution
The solution involves removing trim resistors and diodes, repositioning bandgap resistors to be at least 150 μm from power devices, replacing MOS devices with bipolar devices, and increasing the emitter areas of bipolar devices to reduce offset mismatches and heat effects, thereby eliminating the need for trimming.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If trimming schemes are implemented to correct voltage inaccuracy, then voltage accuracy is improved, but device complexity and manufacturing cost increase
Solution Approach 1:
The patent removes the trimming scheme entirely from the voltage regulator circuit. By extracting the trimming functionality, the circuit becomes simpler with fewer components (no trim resistors or diodes needed), while the voltage accuracy is maintained through improved layout techniques that minimize offset voltages and temperature coefficients during fabrication.
Solution Approach 2:
The patent applies local quality improvements to specific components within the bandgap reference circuit. The emitter areas of bipolar transistors are optimized, and resistors are strategically positioned away from heat-generating power devices. This localized optimization reduces offset voltages and temperature dependencies, achieving accurate voltage regulation without requiring trimming components.
2Measurement precision
If trimming schemes are implemented to correct voltage inaccuracy, then voltage accuracy is improved, but manufacturing time and cost increase
Solution Approach 1:
The patent incorporates preliminary design considerations directly into the fabrication process. The bandgap reference circuit is designed with predetermined emitter areas and resistor placements that pre-compensate for typical fabrication variations. This preliminary action ensures that voltage accuracy is achieved out-of-the-box without requiring post-fabrication trimming operations, thereby reducing manufacturing time and cost.
3Area of stationary object
If resistors are positioned close to power devices for compact layout, then area is reduced, but heat-related inaccuracies increase
Solution Approach 1:
The patent applies local quality considerations to the spatial arrangement of circuit components. Resistors in the bandgap reference circuit are positioned at specific distances from heat-generating power devices, creating localized thermal management zones. This strategic positioning minimizes the impact of thermal gradients on resistor values while maintaining a relatively compact overall circuit footprint.
Solution Approach 2:
The patent employs asymmetric layout techniques where resistors are placed at non-uniform distances from power devices based on their specific thermal sensitivity. This asymmetric arrangement optimizes the trade-off between compactness and thermal isolation, with more thermally sensitive components positioned farther from heat sources while less sensitive components can be placed closer.
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 results in a voltage regulator with improved accuracy and reduced temperature variation, eliminating the need for trimming and associated costs, while minimizing heat-related inaccuracies, achieving a bandgap voltage variation of only 3.5 mV over a temperature range of −40° C. to 125° C.
Implementation Method 1
The Brokaw cell is a bandgap voltage reference circuit based on the addition of two voltages having equal and opposite temperature coefficients (TC). The first voltage is a base-emitter voltage of a forward biased bipolar transistor... The second voltage, which is a Proportional to Absolute Temperature (PTAT) voltage, is formed by amplifying the voltage difference of two forward biased base-emitter junctions of bipolar transistors operating at different current densities.
Implementation Method 2
The first voltage is a base-emitter voltage of a forward biased bipolar transistor. In a typical Brokaw cell (i.e., bandgap cell or circuit), the first voltage has a negative TC of about −2.2 mV/C and is usually denoted as a Complementary to Absolute Temperature (CTAT) voltage.
Implementation Method 3
The second voltage, which is a Proportional to Absolute Temperature (PTAT) voltage, is formed by amplifying the voltage difference of two forward biased base-emitter junctions of bipolar transistors operating at different current densities.
Data Source
AI summary
An optimized output voltage circuit and technique obtainable without trimming is set forth. A voltage reference circuit and method devoid of trim resistors comprising a high gain amplifier, a plurality of bandgap resistors, and at least a plurality of bipolar devices interconnected across circuitry in a predetermined configuration having emitter areas greater than traditional emitter areas of traditional bipolar devices is set forth.