Weak-Inversion Reference Current Circuit With Precise Resistor Trimming
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Solution Overview
Problem
Existing electronic circuits for generating reference currents at low or ultra-low voltages face challenges in trimming a degeneration resistor due to its floating voltage, which complicates achieving precise and reliable reference current values without adverse effects.
Innovation Solution
The circuit incorporates a tap resistor with a tap subcircuit comprising switches and functional transistors, where the switches are grounded at supply line voltages, allowing precise trimming of the resistor resistance without significant voltage drops.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If a degeneration resistor is used in a floating voltage configuration to enable low-voltage operation, then the circuit can operate at low or ultra-low voltages, but the resistor cannot be trimmed precisely due to voltage drops across switch transistors
Solution Approach 1:
The degeneration resistor is divided into multiple segments with different resistance values. Switch transistors are used to selectively connect different segments in parallel, enabling precise trimming of the total resistance. This segmentation allows the resistor to be adjusted in fine steps while maintaining a floating voltage configuration for low-power operation.
Solution Approach 2:
The circuit uses controlled switch transistors to dynamically reconfigure the resistor network. By selectively turning switches on or off, the effective resistance can be changed without physically replacing components. This dynamic trimming capability enables precise resistance adjustment while maintaining the floating voltage configuration necessary for low-voltage operation.
2Adaptability or versatility
If switch transistors are introduced to trim the degeneration resistor, then resistance adjustment is enabled, but voltage drops across the switches degrade trimming precision
Solution Approach 1:
The circuit design ensures that switch transistors operate at matched voltage potentials during trimming operations. By maintaining equipotential conditions across switching nodes, voltage drops across the switches are minimized and compensated, preserving trimming precision while enabling resistance adjustment.
Solution Approach 2:
The invention changes the operating parameters of the switch transistors to minimize their impact on precision. Switches are designed to operate in a specific conduction state with optimized on-resistance, and the trimming process uses parameter adjustments that compensate for switch-induced voltage drops, maintaining high reference current precision.
3Use of energy by moving object
If the degeneration resistor is trimmed at floating voltage, then low-voltage operation is maintained, but trimming reliability is reduced due to lack of reference to supply rails
Solution Approach 1:
The circuit introduces intermediary control circuits that mediate between the floating voltage domain and the supply rail reference domain. These intermediary elements provide stable reference voltages and control signals that enable reliable trimming operations while maintaining the floating voltage configuration for low-power operation.
Solution Approach 2:
The trimming mechanism incorporates feedback loops that monitor the actual resistance value and reference current output. This feedback enables closed-loop trimming control, compensating for variations and ensuring high reliability of the trimming process even in the floating voltage configuration necessary for low-power operation.
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 configuration enables precise and reliable generation of reference currents at low or ultra-low voltages with minimal power consumption, unaffected by temperature dependence and switch-induced errors.
Implementation Method 1
The NMOS transistors 7 and 8, operated in weak inversion region with common source voltage, have the drain current proportional to exp (VGS/[n*VT])
Implementation Method 2
VT is a thermal voltage equal to (k*T/q), in which k is the Boltzmann constant, T the absolute temperature
Implementation Method 3
A drain current ID produces a voltage drop equal to (ID*R) across the resistor 9
Data Source
AI summary
In an electronic circuit for producing a reference current by using weak inversion in MOS transistors (7, 8) while using degeneration in a resistor (10) at a floating voltage along an electric path (4) linking two supply lines (1, 2), adjustment of the reference current is obtained by trimming the resistor. Parallel branches (13) in the electric path (4) can be selectively activated by a switch controller (17) for allowing the current flowing through them. A part of the switches (15) is connected to one of the supply lines at a supply voltage, which allows a precise adjustment.