Reference Voltage Circuit Using Transistor On-Resistance for Low Noise
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Solution Overview
Problem
Conventional band gap reference (BGR) circuits generate noise in the reference voltage, which increases with the ratio of resistors, making it challenging to achieve a constant voltage independent of power supply voltage or temperature.
Innovation Solution
A reference voltage generation circuit incorporating a diode, a first resistor, a transistor, and a control unit that sets the potential of the transistor and diode to the same, with the transistor's on-resistor resistance increasing with temperature, and multiple transistors in parallel to adjust resistance, reducing noise and temperature dependence.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Stability of the object's composition
If a conventional BGR circuit with multiple diodes and resistors is used to generate a constant reference voltage, then temperature compensation can be achieved, but the noise component in the reference voltage increases due to the large resistor ratio required
Solution Approach 1:
The patent changes the key parameter from resistor ratio to transistor on-resistance ratio. By using transistors with different on-resistances (Rds_on1 and Rds_on2) instead of resistors, the circuit achieves temperature compensation while avoiding the noise amplification problem. The transistor's on-resistance naturally varies with temperature, providing the needed temperature dependence without requiring large resistance values that amplify noise.
Solution Approach 2:
The patent substitutes passive resistive elements with active transistor elements. Instead of using resistors whose values are fixed and whose ratio determines temperature compensation, the invention uses transistors whose on-resistance dynamically changes with temperature and process conditions, providing adaptive temperature compensation with lower noise.
2Stability of the object's composition
If the resistor ratio RC/RBGR is increased to improve temperature compensation, then the reference voltage becomes more stable against temperature changes, but the gain with respect to noise increases
Solution Approach 1:
The patent fundamentally changes the parameter used for temperature compensation from resistor ratio (RC/RBGR) to transistor on-resistance ratio (Rds_on1/Rds_on2). This parameter change allows the circuit to achieve temperature compensation through the natural temperature dependence of transistor on-resistance, avoiding the need for large resistance ratios that amplify noise.
3Stability of the object's composition
If a BGR circuit is designed to be independent of power supply voltage, then reference voltage stability is improved, but circuit complexity increases due to additional components and constraints
Solution Approach 1:
The patent makes the transistor serve multiple functions: it provides temperature compensation through its on-resistance temperature dependence, acts as a variable resistor in the voltage division network, and contributes to power supply rejection. This multi-functionality reduces the need for separate dedicated components, simplifying the overall circuit while achieving power supply independence.
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 reduces noise in the reference voltage, maintaining its constancy regardless of power supply voltage or temperature, improving signal quality and stability.
Implementation Method 1
the transistor's on-resistor resistance increasing with temperature
Implementation Method 2
a control unit that controls a potential of the another end of the transistor and a potential of the one end of the diode to the same potential
Data Source
AI summary
A noise component of a reference voltage is reduced in a circuit that generates a constant reference voltage that does not depend on a power supply voltage or a temperature. A reference voltage generation circuit includes a transistor, a first resistor, a diode, a second resistor, and a control unit. One of both ends of the transistor is connected to an output signal line. The first resistor is connected to another end of the transistor. Both ends of the second resistor are connected to one end of the diode and the output signal line. The control unit controls a potential of the another end of the transistor and a potential of the one end of the diode to the same potential.