Bandgap Reference Circuit With Offset Amplifiers for Low Drift
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Solution Overview
Problem
Conventional bandgap reference voltage circuits experience drift in output voltage due to resistor ratio variations over time, making them unsuitable for applications requiring low lifetime drift, and require multiple test insertions at different temperatures for trimming, which increases manufacturing costs.
Innovation Solution
A bandgap reference voltage circuit utilizing a plurality of offset amplifiers to derive the output voltage from a sum of base-emitter voltage differences, reducing dependence on resistor ratios and allowing for adjustable resistance values between sense connections using a multiplexer for fine and coarse adjustments.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If conventional bandgap reference circuits use a single resistor ratio to set output voltage, then the circuit is simple to implement, but the output voltage drifts over time due to resistor ratio variations
Solution Approach 1:
The patent divides the single resistor ratio function into multiple independent resistor ratios (R1/R2, R3/R4, R5/R6) that can be independently adjusted. This segmentation allows each resistor pair to contribute to different aspects of the output voltage, enabling fine-grained control and compensation without requiring a single complex high-precision resistor network.
Solution Approach 2:
The patent introduces dynamic adjustment capability through multiple selectable resistor pairs and trim circuits. The resistor ratios are no longer fixed but can be dynamically selected and adjusted during manufacturing and operation, allowing the circuit to adapt to process variations and compensate for drift over time.
2Manufacturing precision
If multiple test insertions at different temperatures are performed to trim output voltage, then temperature compensation is achieved, but manufacturing cost increases substantially
Solution Approach 1:
The patent performs preliminary trimming at a single temperature point during manufacturing by selecting appropriate resistor pairs and setting trim values. The circuit design incorporates inherent temperature compensation characteristics that eliminate the need for subsequent temperature-based adjustments, reducing manufacturing steps from multiple temperature tests to a single-point trim.
Solution Approach 2:
The patent changes the trimming parameter from temperature-dependent multi-point calibration to single-point voltage adjustment. By using multiple resistor pairs with different temperature coefficients and allowing independent adjustment of each pair, the circuit achieves temperature compensation through parameter selection rather than iterative temperature testing.
3Ease of manufacture
If resistor ratio varies by 200 ppm, then the circuit is easy to manufacture with standard tolerances, but the output voltage varies by around 100 ppm which may exceed drift limits
Solution Approach 1:
The patent segments the output voltage determination into multiple independent resistor ratio contributions. Instead of relying on a single resistor ratio where 200 ppm variation directly translates to 100 ppm output drift, the circuit uses multiple resistor pairs where each contributes partially to the final output, allowing error distribution and cancellation across segments.
Solution Approach 2:
The patent incorporates feedback mechanisms through the interconnected transistor-resistor network where variations in one resistor ratio are compensated by adjustments in other ratios. The circuit topology provides inherent feedback that stabilizes the output voltage against individual resistor variations, reducing the direct transmission of tolerance errors to the final output.
Data Source
AI summary
The disclosure relates to a bandgap reference voltage circuit, in which an output reference voltage is stable with respect to temperature and other variations. Example embodiments include a bandgap reference voltage circuit comprising an output voltage circuit and a plurality, n, of offset amplifiers connected between first and second voltage rails, each of the plurality of offset amplifiers comprising a differential pair of transistors that together define an offset between an input voltage at an input and an output of the amplifier, the offset amplifiers being chained together and connected to the output voltage circuit that provides a bandgap reference voltage dependent on a sum of the offsets of the plurality of offset amplifiers.