Band Gap Reference Voltage Generator Bidirectional Trimming
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Solution Overview
Problem
Conventional band gap reference voltage generators face challenges in achieving bidirectional resistance trimming with minimal ON resistance, leading to increased IC area consumption and inaccuracy due to variability in supply voltage and switch resistance.
Innovation Solution
A band gap reference voltage generator design that includes a voltage divider configuration with controllable switch elements and a voltage error amplifier, allowing for bidirectional adjustment of the voltage divider ratio using a multiplexer and decoder, reducing the number of trim resistors and switch elements while maintaining precision.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If trim switches with small ON resistance are used to reduce trimming inaccuracy, then trimming precision is improved, but IC area consumption increases
Solution Approach 1:
The patent applies the dynamics principle by making the reference voltage dynamically adjustable through bidirectional trimming. The trim switches are configured to enable both increasing and decreasing of the reference voltage, allowing the system to adapt to different process variations. This dynamic adjustment capability improves trimming precision without requiring excessively low ON resistance switches, as the system can compensate for switch resistance effects through bidirectional adjustment.
Solution Approach 2:
The patent inverts the conventional unidirectional trimming approach by implementing bidirectional trimming capability. Instead of only increasing or only decreasing the reference voltage, the circuit can adjust in both directions. This inversion allows the use of switches with higher ON resistance, as the bidirectional capability compensates for resistance effects, thereby reducing IC area consumption while maintaining trimming precision.
2Device complexity
If unidirectional trimming is used, then device complexity is reduced, but adaptability deteriorates
Solution Approach 1:
The patent implements dynamic adaptability by enabling bidirectional trimming of the reference voltage. The circuit can adjust the voltage in both increasing and decreasing directions, allowing it to adapt to various process variations and operating conditions. This dynamic capability is achieved through a relatively simple circuit configuration that uses switch pairs controlled by complementary signals, maintaining low complexity while high adaptability.
Solution Approach 2:
The patent achieves universality by designing a trimming circuit that can handle both upward and downward adjustments using the same basic circuit structure. The switch pairs and capacitor configuration serve multiple functions: they enable bidirectional adjustment, provide hysteresis for stability, and allow digital control. This multi-functionality increases adaptability without significantly increasing device complexity.
3Reliability
If hysteresis is introduced to improve stability, then reliability is improved, but device complexity increases
Solution Approach 1:
The patent introduces dynamic hysteresis through the capacitor connected to the switching circuit. The capacitor stores charge and creates a voltage offset that provides hysteresis, improving output stability and preventing oscillations during trimming. This dynamic hysteresis mechanism is achieved with minimal additional components, maintaining low circuit complexity while significantly improving reliability.
Solution Approach 2:
The patent uses a capacitor as an intermediary element to introduce hysteresis into the trimming circuit. The capacitor acts as a mediator between the switch pair and the reference voltage output, storing energy and creating the hysteresis effect. This intermediary approach provides stability improvement without requiring complex circuit structures, as the single capacitor element suffices to create the desired hysteresis behavior.
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 design achieves precise temperature compensation with reduced IC area consumption and improved accuracy by allowing bidirectional trimming and minimizing the impact of ON resistance variations, resulting in a more efficient and compact integrated circuit.
Implementation Method 1
The voltage across a forward-biased semiconductor PN junction for a given current through the junction decreases with increasing temperature, commonly called complementary to absolute temperature (CTAT), varying by approximately −2 mV/° K in a silicon semiconductor, for example.
Implementation Method 2
A band gap module uses a voltage difference between a pair of matched forward-biased PN junctions operating at different current densities to generate a current that increases with increasing temperature, commonly called proportional to absolute temperature (PTAT).
Data Source
AI summary
A band gap reference voltage generator has first and second current conduction paths between a first node and a second node. The first current conduction path has first resistive elements in series with a first forward-biased PN junction element. A tap is connected selectively to the first resistive elements through switches that are controllable to select a voltage divider ratio at the tap. The second current conduction path includes a second resistive element in series with a second PN junction element of greater current density than the first PN junction. A voltage error amplifier has inputs connected to the tap and the second PN junction element, and an output for providing a thermally compensated output voltage VREF. A feedback path applies the output voltage VREF through a third resistive element to the first node.