Resistor-Less Bias Current Generator Using MOS Triode Region
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Solution Overview
Problem
Existing bias current generators in silicon-based integrated circuits face challenges such as high die area and cost due to the use of resistors for low power applications, and they often have temperature-dependent performance.
Innovation Solution
A bias current generator using MOS devices to generate a current related to the voltage difference between bipolar transistors operating at different current densities, where the voltage difference is reflected across MOS devices configured as resistors to produce a proportional current, eliminating the need for resistors and optimizing silicon area usage.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If resistors are used to generate bias current in low power applications, then the bias current can be generated, but the die area and cost increase
Solution Approach 1:
The patent changes the operating parameters of MOS transistors by controlling their channel width-to-length ratios to operate in the triode region, where they exhibit resistive behavior. This allows the circuit to achieve the current-generating function of resistors while using MOS devices that can be more densely integrated, thereby reducing die area while maintaining low power consumption
Solution Approach 2:
The patent creates a functional copy of resistor behavior using MOS transistors operating in the triode region. By controlling the aspect ratios of the MOS devices, the circuit replicates the voltage-to-current conversion function of resistors without requiring actual resistor elements, thus reducing die area while maintaining the desired low power operation
2Use of energy by moving object
If resistors are used to generate bias current, then the current can be generated, but the precision and trimming capability are limited
Solution Approach 1:
The patent introduces dynamic control capability by using MOS transistors whose effective resistance can be adjusted through aspect ratio design and gate voltage control. This dynamic characteristic enables trimming mechanisms to precisely adjust the bias current by modifying the channel dimensions or operating conditions of the MOS devices, providing both precision and adaptability while maintaining low power consumption
Solution Approach 2:
The patent enables precision trimming by allowing parameter changes in the MOS transistor characteristics. By controlling the aspect ratios and operating points of the MOS devices, the circuit can be trimmed to optimize bias current precision, overcoming the fixed nature of physical resistors while maintaining low power operation
3Quantity of substance
If bipolar transistors are used to generate PTAT voltage, then temperature-dependent current can be generated, but temperature independence is not achieved
Solution Approach 1:
The patent employs feedback mechanisms where the PTAT voltage generated by bipolar transistors is used to control the gate voltages of MOS transistors operating as resistors. This feedback loop allows the circuit to compensate for temperature variations by adjusting the MOS device operating points, thereby achieving temperature-independent bias current output while maintaining proper current generation across temperature ranges
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 solution enables a low power, resistor-less bias current generator that occupies less silicon area, operates at low supply voltages, and allows for temperature-independent performance, with the ability to trim the bias current for precision and cost-effectiveness.
Implementation Method 1
The PTAT current is related to the ratio of the ΔVBE to the RON of the MOS device
Data Source
AI summary
A bias current generators that may be implemented in low power environments is described. The current generator can be implemented without using resistors and may be used to generate reference currents and voltages. It may also be used to generate voltage references where the output of the circuit is to at least a first order temperature independent.