Drain-Coupled MOS Reference Circuit for Low-Voltage Operation
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Conventional bandgap reference circuits face challenges in low-power applications due to limited voltage headroom, making it difficult to operate effectively in low-voltage, low-power environments.
Innovation Solution
The development of MOS reference circuits that utilize drain-coupled metal oxide semiconductor (MOS) transistors to generate a reference current, employing a common-source configuration with coupled drains and feedback loops for stable current regulation, along with thermal compensation techniques to maintain reliability across a wide range of power supply and temperature conditions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional bandgap reference circuits are used, then reference current or voltage can be generated through p-n junctions operated at different current densities, but the circuits require higher supply voltages and consume more power, making them unsuitable for low-power applications
Solution Approach 1:
The patent replaces the conventional bandgap reference circuit architecture (which uses p-n junctions and requires high voltage headroom) with a drain-coupled MOS transistor configuration. This substitution enables the reference current to be generated using only the gate-to-source voltage difference of two MOS transistors, eliminating the need for complex biasing circuits and reducing power consumption while maintaining reference stability
Solution Approach 2:
The invention changes the operating parameters by using MOS transistors in saturation mode with different width-to-length ratios to create a voltage difference, rather than using p-n junctions at different current densities. This parameter change allows the circuit to operate at lower supply voltages (1.8V to 5.5V) and reduces power consumption while maintaining temperature compensation through the PTAT current generation
2Reliability
If conventional bandgap reference circuits are used, then reference voltage can be derived from p-n junctions, but the circuits require sufficient voltage headroom which limits their operation in low-voltage environments
Solution Approach 1:
The patent substitutes the p-n junction-based voltage derivation mechanism with a MOS transistor-based voltage difference generation mechanism. The drain-coupled MOS configuration generates the reference voltage directly from the gate-to-source voltage difference, eliminating the voltage headroom requirements of conventional bandgap circuits and enabling operation across a wide voltage range (1.8V to 5.5V)
Solution Approach 2:
The drain-coupled MOS transistor circuit serves multiple functions: it generates the PTAT current, provides temperature compensation, and operates across a wide supply voltage range, making the reference circuit universally applicable to both low-voltage and standard-voltage applications without requiring circuit redesign
3Reliability
If p-n junctions are operated at different current densities to generate PTAT current, then temperature compensation can be achieved, but the circuit complexity and power consumption increase
Solution Approach 1:
The patent merges the temperature compensation function with the reference current generation function by using the same drain-coupled MOS transistor configuration to both generate the PTAT current and provide thermal compensation. This integration eliminates the need for separate compensation circuits, reducing overall circuit complexity while maintaining temperature stability
Solution Approach 2:
The MOS transistor configuration inherently provides temperature compensation through its own characteristics - the gate-to-source voltage difference automatically tracks temperature variations, and the feedback mechanism uses this information to maintain a stable reference current without requiring external compensation elements
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
These circuits provide reliable current line regulation and flexibility for thermal compensation, enabling operation within a low-voltage range of 1.7V to 5.6V, with the ability to function at lower voltages and maintain stability across varying temperatures, thus addressing the limitations of conventional bandgap reference circuits in low-power applications.
Implementation Method 1
The reference circuit applies the difference of gate-to-source voltages of two MOS transistors across a resistor to produce a reference current. The MOS transistors are configured with their drains connected to provide the same drain-to-source (VDS) condition for both devices.
Implementation Method 2
A feedback loop preserves the level of current flowing through the reference resistor.
Implementation Method 3
employing thermal compensation techniques to maintain reliability across a wide range of power supply and temperature conditions
Data Source
AI summary
A reference circuit includes a first transistor having a first current electrode, a control electrode, and a second current electrode coupled to a power supply terminal. The reference circuit further includes a resistive element including a first terminal coupled to the control electrode of the first transistor and a second terminal coupled to the first current electrode. Additionally, the reference circuit includes a second transistor including a first current electrode coupled to the second terminal of the resistive element, a control electrode coupled to the second terminal, and a second current electrode coupled to the power supply terminal. The second transistor is configured to produce an output signal related to a voltage at the control electrode of the first transistor.