Bandgap Reference Circuit Trimming with Replica Elements
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Solution Overview
Problem
Existing bandgap reference circuits face challenges in providing a precise voltage across a wide range of temperatures due to errors caused by process variations, mismatch, and package-induced stresses, which cannot be effectively addressed by existing trimming methods.
Innovation Solution
A bandgap reference circuit with a trimming network and replica elements, where the resistance of the trimming network is set based on measured diode and resistor voltages and resistances, allowing for single-trim at room temperature to achieve precise bandgap reference voltage across a wide temperature range.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If existing trimming methods are used to address process variations and mismatch, then manufacturing precision is improved, but the precision of bandgap reference voltage across wide temperature range deteriorates due to package-induced stresses
Solution Approach 1:
The patent applies preliminary action by performing trimming at a specific reference temperature (e.g., room temperature) before the circuit operates across its full temperature range. The trimming network is configured and adjusted at this predetermined temperature point to establish baseline parameters, which then compensate for temperature-induced variations during subsequent operation. This preliminary trimming action addresses package-induced stresses by establishing accurate reference values before thermal expansion and stress effects manifest during temperature cycling.
Solution Approach 2:
The patent employs parameter changes by utilizing the trimming network to adjust specific circuit parameters (such as resistor ratios or current scaling factors) based on measurements taken at a reference temperature. These parameter adjustments are designed to counteract the effects of temperature variations on the bandgap reference voltage. The trimming network modifies circuit parameters to compensate for both process variations and temperature-dependent effects including package-induced stresses, thereby maintaining precision across the full operating temperature range.
2Temperature
If multiple trimming operations are performed across different temperatures, then temperature accuracy is improved, but productivity deteriorates due to increased trimming time and complexity
Solution Approach 1:
The patent performs the trimming operation at a single predetermined reference temperature (e.g., room temperature) before the circuit enters its operational temperature range. This preliminary trimming action establishes the necessary compensation parameters in advance, eliminating the need for multiple trimming operations at different temperatures. The trimming network is configured once during manufacturing or initialization, significantly reducing trimming time and improving productivity while still achieving accurate compensation across the full temperature range through the circuit's inherent temperature compensation mechanisms.
3Productivity
If trimming is performed at room temperature only, then productivity is improved by reducing trimming steps, but manufacturing precision deteriorates due to inability to compensate for temperature-dependent errors
Solution Approach 1:
The patent adjusts specific circuit parameters through the trimming network at room temperature to establish compensation characteristics that remain effective across the full operating temperature range. The trimming process modifies parameters such as resistor ratios, current scaling factors, or transistor sizing relationships in a way that creates temperature-invariant reference voltage characteristics. By carefully selecting which parameters to trim and how to configure the trimming network, the system achieves both high trimming efficiency (single-temperature operation) and high manufacturing precision (accurate voltage reference across temperature) simultaneously.
Solution Approach 2:
The patent incorporates feedback mechanisms where the trimming process uses measured voltage values from the bandgap reference circuit to automatically adjust the trimming network parameters. During trimming at room temperature, the circuit measures its own output voltage and uses this feedback information to determine the appropriate trimming adjustments needed. This feedback-based trimming ensures that the single-temperature trimming operation achieves the precise voltage reference level required for accurate operation across the entire temperature range, without requiring manual intervention or multiple temperature points.
Data Source
AI summary
A method and circuit for trimming a bandgap reference are described. The bandgap reference circuit comprises a first diode which is arranged in series with a first resistor between a reference point and a reference potential VSS. The circuit also comprises a second diode which is arranged in series with a second resistor and a third resistor between the reference point and the reference potential VSS. In addition, the bandgap reference circuit comprises a trimming network, wherein a bandgap reference voltage VBG CORE is provided at a midpoint between the trimming network and the current source. The circuit also comprises an operational amplifier. The method (700) comprises measuring a first diode voltage across a replica element of the first diode; determining a first resistance of a replica element of the first resistor; and setting a resistance of the trimming network using the first diode voltage and the first resistance.