On-Chip Current Mirror Circuit for Temperature-Independent Bias Current
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Solution Overview
Problem
Conventional current generators that produce temperature-independent currents in CMOS technology face challenges in implementing temperature-independent reference voltages and resistances, requiring precise trimming and are difficult to integrate on-chip.
Innovation Solution
An on-chip temperature-independent current generator using a CMOS current mirror with an on-chip bipolar NPN transistor and a temperature-independent reference voltage generator, where the current mirror replicates the collector current to generate a temperature-independent current, eliminating the need for trimming.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Stability of the object's composition
If conventional voltage to current converter circuits with temperature independent reference voltage band gap are used, then temperature independent current can be generated, but implementation in CMOS technology is difficult
Solution Approach 1:
The circuit is divided into distinct functional blocks: a bandgap reference voltage generator (providing temperature-independent voltage), a PTAT current generator (providing temperature-proportional current), and a summing node. This segmentation allows each block to be optimized independently for CMOS compatibility while maintaining overall temperature independence.
Solution Approach 2:
The patent combines two temperature-dependent current paths (PTAT current through first transistor and CTAT current through second transistor) into a single summing node where their temperature dependencies cancel out, producing a temperature-independent output current. This merging approach achieves temperature compensation without requiring external trimming components.
2Stability of the object's composition
If conventional current generators with current DACs and current mirrors are used, then temperature independent current can be generated, but precise trimming of temperature dependency compensation is required
Solution Approach 1:
The circuit automatically compensates for temperature variations through its inherent structure. The bandgap reference provides a temperature-independent voltage that automatically adjusts the bias conditions, while the summing of PTAT and CTAT currents inherently cancels temperature dependencies without requiring external trimming or calibration procedures.
Solution Approach 2:
The patent changes the operating parameters of the transistors and resistors such that their temperature coefficients are matched to achieve automatic compensation. By carefully selecting transistor dimensions and resistor ratios, the circuit achieves temperature independence through parameter matching rather than post-fabrication trimming.
3Stability of the object's composition
If temperature independent reference voltage band gap and temperature independent resistance are used, then temperature independent current can be generated, but it is difficult to implement in CMOS technology
Solution Approach 1:
The bandgap reference circuit serves multiple functions: it provides a temperature-independent reference voltage for the current generator, and its output is also used to bias the PTAT and CTAT current paths. This multi-functionality reduces the need for separate dedicated components, simplifying the overall CMOS implementation.
Solution Approach 2:
The patent introduces intermediate current paths (PTAT and CTAT currents) that act as mediators between the bandgap reference voltage and the final temperature-independent output current. These intermediary currents allow the temperature compensation to be achieved through current summation rather than direct voltage-to-current conversion, simplifying the CMOS implementation.
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 provides a temperature-independent current across a wide range (-60°C to +200°C) with a nominal current amplitude of 0.6 to 1.0 µAmp, effectively addressing the integration and trimming challenges of conventional generators.
Implementation Method 1
an on chip current generator (3) having an output (4) to provide an electrical current (IPTAT) being proportional to an absolute temperature (T) of the chip
Implementation Method 2
the current mirror (12) is adapted to mirror a collector current (IC) flowing to the collector of the on chip transistor (9) to generate the temperature independent current (Iout)
Data Source
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AI summary
An on chip temperature independent current generator, TICG, (1) for generating a temperature independent current (Iout), said TICG (1) comprising an on chip current generator (3) having an output (4) to provide an electrical current (IPTAT) having a current amplitude being proportional to a temperature (T) of said chip; an on chip transistor (9) having a base (B) connected to a temperature independent reference voltage generator (10), a collector (C) connected to a current mirror (12) and an emitter (E) connected to the output (4) of the on chip current generator (3) and connected via an on chip resistor (14) to a reference potential (GND); wherein the current mirror (12) is adapted to mirror a collector current (Ic) flowing to the collector (C) of said on chip transistor (9) to generate the temperature independent current (Iout).