Bandgap Reference Circuit With Current Mirrors for Low-Noise Stability
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Solution Overview
Problem
Bandgap reference circuits face challenges in generating accurate voltage references over a wide range of supply voltages and temperatures due to multiple operating points and inaccuracies caused by offset voltages and current mirroring, especially in deep sub-micron processes.
Innovation Solution
A circuit design incorporating a first and second current mirror circuit, amplifier, and start-up circuit that generates a temperature-compensated bandgap voltage by mirroring averaged currents through diode-connected PFETs, ensuring minimal impact from transistor mismatches and reducing quiescent current, while the start-up circuit ensures rapid and correct operating point attainment.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by stationary object
If conventional bandgap reference circuits are used to provide voltage references, then the circuits can operate over a range of temperatures and process variations, but the circuits consume relatively high amounts of power and have high quiescent current
Solution Approach 1:
The bandgap reference circuit is divided into multiple independent stages: a first current mirror circuit, a first stage, a second stage, and an amplifier. Each stage processes currents separately and contributes to the final bandgap voltage in a controlled manner, allowing power consumption to be optimized at each stage while maintaining overall reference stability.
Solution Approach 2:
The circuit uses temperature-dependent parameters (such as base-emitter voltage differences between transistors operating at different current densities) to generate a compensated bandgap voltage. By carefully selecting transistor areas and current ratios, the circuit achieves temperature independence while operating at lower quiescent currents.
2Adaptability or versatility
If bandgap reference circuits are designed to turn on early and stay on as long as possible, then the voltage reference is available across wide operating ranges, but the circuits consume more power
Solution Approach 1:
The circuit employs dynamic current mirroring where the first and second current mirror circuits actively track and replicate current relationships across varying supply voltages. This dynamic adaptation allows the circuit to maintain accurate bandgap reference operation from low supply voltages (e.g., 1.2V) up to higher voltages, extending the operating range while consuming power only when needed.
Solution Approach 2:
The current mirror circuits serve multiple functions: they provide current scaling, voltage level shifting, and temperature compensation simultaneously. This multi-functionality allows a single circuit architecture to operate effectively across wide supply voltage ranges (1.2V to 5V or more) without requiring separate circuits for different voltage domains.
3Reliability
If current mirroring is used in bandgap reference circuits, then the circuits can provide stable voltage references, but inaccuracies occur due to offset voltages and transistor mismatches
Solution Approach 1:
The amplifier provides negative feedback that continuously monitors and corrects for offset voltages and current mismatches in the current mirror circuits. By comparing the actual current relationships with the ideal relationships and adjusting accordingly, the circuit compensates for manufacturing variations and maintains high accuracy in the generated bandgap voltage.
Solution Approach 2:
The first and second current mirror circuits act as intermediaries that isolate and buffer the sensitive bandgap voltage generation from load variations and noise. The mirrors transfer current relationships with high fidelity while providing impedance transformation, reducing the impact of direct connections and parasitic effects on accuracy.
4Area of stationary object
If deep sub-micron processes are used to reduce circuit size, then integration is improved, but inaccuracies increase due to offset voltages and current mirroring effects
Solution Approach 1:
The circuit exploits the temperature dependence of base-emitter voltages in bipolar transistors, using transistors with different areas (Q1 with area A1, Q2 with area A2) operating at different current densities to generate a voltage difference that is proportional to temperature. This temperature-dependent parameter is then combined with the PTAT current to create a voltage that is independent of temperature variations, achieving high accuracy despite the small geometric dimensions of deep sub-micron transistors.
Data Source
AI summary
In described examples, a circuit includes a first current mirror circuit. The first current mirror circuit is coupled to a power input terminal. A first stage is coupled to the first current mirror circuit, and a second stage is coupled to the first stage and to the first current mirror circuit. An amplifier is coupled to the first and second stages. The amplifier has first and second input terminals. The first input terminal is coupled to the first stage, and the second input terminal is coupled to the second stage. A second current mirror circuit is coupled to the first stage, the second stage and the amplifier.