Bandgap Circuit Base Current Compensation for Beta Spread
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Solution Overview
Problem
In modern CMOS processes, the characteristics of bipolar transistors, particularly Beta, are difficult to control due to low Beta values and significant base recombination current, leading to inaccuracies in bandgap voltage generation and temperature sensing.
Innovation Solution
A compensation circuit is introduced to adjust the base current of bipolar transistors, using a resistor or active circuitry to regulate base current fluctuations, effectively canceling out Beta spread and improving temperature sensing accuracy.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If bipolar devices are used for temperature sensing based on base-emitter voltage difference, then temperature sensing capability is achieved, but Beta spread between devices causes measurement inaccuracy
Solution Approach 1:
The patent introduces a feedback mechanism where the voltage difference (ΔVbe) between two bipolar devices with different emitter areas is amplified and used to adjust the base currents. The amplifier circuit continuously monitors the voltage difference and adjusts the currents to maintain a proportional relationship, compensating for Beta variations and improving temperature sensing accuracy.
Solution Approach 2:
The patent changes the operating parameters by using bipolar devices with different emitter areas (Area1 and Area2) and adjusting their base currents proportionally. By varying the emitter area parameter and controlling the base current ratio, the circuit compensates for Beta spread effects and achieves more accurate temperature sensing.
2Ease of operation
If base recombination current is significant in bipolar devices, then device operation is maintained, but temperature sensing accuracy deteriorates due to low Beta values
Solution Approach 1:
The amplifier circuit provides continuous feedback to adjust the base currents of the two bipolar devices. By monitoring the voltage difference and dynamically adjusting the currents, the system compensates for base recombination effects and maintains accurate temperature sensing even when Beta values are low.
Solution Approach 2:
The patent uses asymmetric bipolar devices with different emitter areas (Area1 ≠ Area2). This asymmetry creates a measurable voltage difference that is proportional to temperature, allowing the circuit to operate effectively with significant base recombination current while maintaining sensing accuracy through proper current ratio control.
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
The compensation circuit enhances the accuracy of temperature sensing by controlling base current variations, leading to more precise temperature readings and improved performance in integrated circuits.
Implementation Method 1
an amplifier circuit configured to generate the bias voltage using a first voltage drop across the first bipolar device and a second voltage drop across the series combination of the bias resistor and the second bipolar device
Implementation Method 2
A compensation circuit is also included, where the compensation circuit is configured to adjust, based on a value of the bias resistor, a base current of the second bipolar device
Implementation Method 3
The current through the base of the second bipolar device, representing the beta spread with temperature, may be controlled based on a ratio of resistances of the bias resistor to the compensation circuit resistor
Data Source
AI summary
A bandgap circuit is disclosed. The bandgap circuit includes a current source configured to generate, using a bias voltage, a first current and a second current, a first bipolar device configured to sink the first current, and a second bipolar device configured to sink the second current via a bias resistor. The bandgap circuit further includes an amplifier circuit configured to generate the bias voltage using a first voltage drop across the first bipolar device and a second voltage drop across the series combination of the bias resistor and the second bipolar device. A compensation circuit is also included, where the compensation circuit is configured to adjust, based on a value of the bias resistor, a base current of the second bipolar device.