Current Reference Circuit Using Transistor Current Difference
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Solution Overview
Problem
Conventional current reference circuits in semiconductor devices occupy a large area and are prone to resistor mismatch issues due to fabrication variations and temperature changes, affecting their stability and operation.
Innovation Solution
A method and circuit that generate a reference current using NMOS and PMOS transistors, calculating a current difference and multiplying it by a proportional constant to create a third current with a similar temperature slope, then subtracting this from the PMOS current to produce a temperature-stable reference current, eliminating the need for separate PTAT and CTAT current components and resistors.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional band gap reference circuits with separate PTAT and CTAT generating units are used, then temperature compensation is achieved, but chip area occupancy increases
Solution Approach 1:
The patent combines the PTAT and CTAT current generating functions into a single band gap reference circuit structure. The first and second current generating units share common circuit elements and topology, integrating temperature compensation functionality without requiring separate dedicated circuits for PTAT and CTAT generation, thereby reducing overall chip area while maintaining temperature stability
2Reliability
If resistors are used in conventional current reference circuits for generating PTAT and CTAT currents, then temperature compensation is achieved, but resistor mismatch occurs due to fabrication variations and voltage variations
Solution Approach 1:
The patent extracts and eliminates the resistor elements from the current reference circuit. Instead of using resistors to generate PTAT and CTAT currents, the invention uses transistor-based current mirrors and biasing circuits that are less sensitive to fabrication variations and voltage changes, thereby removing the source of resistor mismatch while preserving temperature compensation functionality
Solution Approach 2:
The patent changes the fundamental operating parameters and mechanisms of the circuit from resistor-based current generation to transistor-based current generation. By utilizing transistor threshold voltages, current mirrors, and biasing techniques, the circuit achieves temperature compensation through transistor characteristics rather than resistor ratios, which are more stable against process variations
3Reliability
If conventional current reference circuits are used, then reference current is generated, but the circuit is sensitive to voltage variations and local temperature variations
Solution Approach 1:
The patent incorporates feedback mechanisms through current mirrors and biasing circuits that continuously monitor and adjust the reference current. The circuit uses feedback loops that sense variations in supply voltage and local temperature, and automatically compensate for these variations by adjusting transistor gate voltages and current levels, thereby maintaining stable reference current output despite external disturbances
Data Source
AI summary
Provided are a reference current generating method and a current reference circuit. The reference current generating method includes generating a first current using a NMOS transistor and a second current using a PMOS transistor, calculating a current difference between the first and second currents, generating a third current which has a similar current/temperature slope as the second current by multiplying the current difference by a proportional constant, and generating a reference current by subtracting the third current from the second current.