Delta-Vbe Reference Voltage Circuit Using Thin-Film Resistors
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Conventional delta-Vbe circuits face challenges in reducing 1/f noise and require high voltage supply due to the use of current mirrors and cross-connected quad BJT structures, which also increase circuit area and complexity.
Innovation Solution
The proposed delta-Vbe circuit employs thin-film resistors instead of active current mirrors, eliminating the need for stacked BJTs and allowing operation with a lower voltage supply, thereby reducing 1/f noise and circuit area.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Stability of the object's composition
If current mirrors and cross-connected quad BJT structures are used in delta-Vbe circuits, then temperature stability is achieved, but 1/f noise increases and circuit area expands
Solution Approach 1:
The patent extracts and eliminates the current mirror structure from the delta-Vbe circuit, replacing it with a simplified transistor pair configuration. This removal of the harmful current mirror element reduces 1/f noise while maintaining the temperature compensation function through direct voltage subtraction of the two transistors with different current densities
Solution Approach 2:
The patent uses two copies of the basic transistor structure (Q1 and Q2) with different emitter areas, creating a scaled version of the same circuit topology. This copying approach allows temperature compensation without requiring complex current mirrors, as the scaled transistor pair directly generates the compensating voltage
2Stability of the object's composition
If current mirrors and cross-connected quad BJT structures are used, then temperature compensation is achieved, but circuit area increases
Solution Approach 1:
The patent removes the redundant current mirror structures and cross-connected quad BJT configurations, retaining only the essential scaled transistor pair (Q1, Q2) with different emitter areas. This extraction eliminates unnecessary area-consuming components while preserving the core temperature compensation mechanism
Solution Approach 2:
The circuit is segmented into two independent but scaled transistor paths (Q1 with area A1 and Q2 with area A2) that can be independently sized and positioned. This segmentation allows flexible layout optimization and reduces overall circuit area compared to the interconnected quad BJT structure
3Measurement precision
If stacked BJTs are used in conventional delta-Vbe circuits, then voltage reference is generated, but voltage supply requirement increases
Solution Approach 1:
Instead of stacking BJTs in series to generate the voltage reference (which increases voltage headroom requirements), the patent inverts the approach by using parallel-scaled transistors with different current densities. The voltage reference is generated through the voltage difference across these parallel structures, eliminating the need for high voltage supply while maintaining measurement precision
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 effectively minimizes 1/f noise and reduces the overall circuit area, achieving a temperature-stable reference voltage with lower noise and lower voltage requirements.
Implementation Method 1
The voltage across the transistor is proportional to the thermal voltage, VT, where V=VT*ln(IC/IS) and VT=k*T/q, where k is the Boltzmann's constant, q is the electron charge, and T is the absolute temperature
Implementation Method 2
A bandgap voltage reference circuit is a temperature independent voltage reference circuit widely used in integrated circuits. Such a circuit is designed to produce a fixed voltage regardless of temperature changes. One example of a bandgap voltage reference circuit combines a complementary to absolute temperature (CTAT) circuit and a proportional to absolute temperature (PTAT) circuit to obtain a voltage relatively insensitive to temperature.
Data Source
AI summary
A delta-Vbe based bandgap reference voltage circuit generates a temperature stable reference voltage. First and second paths of the circuit each include a respective transistor coupled in series with a resistance. The collector current density of the transistor in first path is lower than the collector current density of transistor in the other path. A control path is used to generate a 2Vbe voltage that is coupled to the base nodes of the resistors in each path. A resistance that is coupled between a common node of a first end of the two paths and a circuit ground node. The circuit current is controlled by this resistance and a voltage drop of 2ΔVbe is across the resistance. The output reference voltage of the circuit is 2(Vbe+ΔVbe) when stack resistors in each path are used.