Bias Current Generator Using Negative Threshold Transistors
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Existing bias current generators for low power chips are area-intensive, time-consuming, and costly to trim due to the use of poly resistors, which require multiple measurements and can introduce scaling errors.
Innovation Solution
A bias current generator using two or more negative threshold transistors coupled in series, optionally with a current mirror and cascode transistor, allows for faster and more accurate measurement of bias current through threshold voltage measurement, and enables efficient trimming via a look-up table.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Area of stationary object
If a poly resistor is used in the bias current generator, then the bias current can be generated, but the circuit occupies a significant area on the chip
Solution Approach 1:
The patent changes the fundamental parameter of the resistive element from poly resistor to negative threshold transistor. This parameter change enables the generation of bias current while occupying significantly less chip area, as transistors have a much smaller footprint compared to poly resistors required for the same current generation function.
Solution Approach 2:
The patent substitutes the poly resistor (passive component) with a negative threshold transistor (active component). This substitution replaces the traditional resistive mechanism with a transistor-based mechanism that utilizes the negative threshold voltage characteristic to generate bias current, thereby reducing area while maintaining functionality.
2Loss of time
If the poly resistor is scaled down to decrease resistance, then measurement speed improves, but scaling errors are introduced
Solution Approach 1:
The patent employs negative threshold transistors that do not require long settling times for measurement. The bias current can be measured directly without waiting for charge accumulation or discharge processes, enabling faster measurement while avoiding the scaling errors associated with reduced resistor dimensions.
3Loss of time
If the bias current is scaled up for measurement, then measurement speed improves, but scaling errors are introduced
Solution Approach 1:
The patent uses a current mirror to create an accurate copy of the bias current for measurement purposes. The current mirror replicates the nanoampere bias current without requiring scaling, allowing direct measurement of the actual bias current value while maintaining measurement accuracy and avoiding scaling errors.
4Measurement precision
If multiple measurements are performed to evaluate bias current, then measurement accuracy improves, but trimming time and cost increase
Solution Approach 1:
The negative threshold transistor inherently provides stable bias current generation through its device physics characteristics. The transistor's negative threshold voltage creates a self-regulating effect that stabilizes the bias current, reducing the need for multiple measurements and extensive trimming procedures while maintaining accuracy.
Data Source
AI summary
An apparatus comprising a bias current generator for generating a bias current, the bias current generator comprising two or more negative threshold transistors of the same type and coupled in series.