Reference Voltage Circuit Temperature Compensation
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Solution Overview
Problem
Existing reference voltage generating circuits using Brokaw cells face challenges in maintaining a constant reference voltage across varying temperatures due to variations in transistor and resistor characteristics, leading to tilted temperature dependence curves.
Innovation Solution
A reference voltage generating circuit with bipolar transistors and variable resistors, employing differential amplifiers and current mirror circuits for low- and high-temperature compensation, adjusts the temperature dependence by using correction currents and variable resistors to flatten the temperature slope and stabilize the reference voltage.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Temperature
If a Brokaw cell with temperature compensating circuit is used to generate reference voltage, then the temperature dependence is compensated in low- and high-temperature regions, but the reference voltage still exhibits tilted temperature dependence due to variations in transistor and resistor characteristics
Solution Approach 1:
The patent introduces dynamically adjustable resistors (switchable resistors) that can change their resistance values based on detected temperature ranges. This dynamic adjustment compensates for the tilted temperature dependence caused by element variations, allowing the circuit to maintain accurate reference voltage across different temperature conditions rather than relying on fixed compensation values.
Solution Approach 2:
The patent changes the resistance parameters of the compensating resistors based on temperature conditions. By switching between different resistor values corresponding to different temperature ranges, the circuit adapts the compensation amount to match the actual temperature-dependent variations in transistor and resistor characteristics, thereby flattening the temperature dependence curve.
2Device complexity
If fixed resistors are used in the temperature compensating circuit, then the circuit structure is simple, but the reference voltage varies due to unintended variations in current sources and element characteristics
Solution Approach 1:
The patent replaces fixed resistors with dynamically switchable resistors that can adjust their resistance values based on temperature ranges. This dynamic configuration allows the circuit to compensate for element variations and current source uncertainties, significantly improving reference voltage stability while adding only moderate complexity through the switchable resistor network.
3Manufacturing precision
If the area ratio of transistor emitter areas is fixed at A:1, then the Brokaw cell operates with defined current ratios, but variations in transistor characteristics cause tilted temperature dependence that cannot be fully compensated
Solution Approach 1:
The patent introduces switchable resistors that can change their resistance values based on temperature ranges, compensating for the tilted temperature dependence caused by fixed transistor area ratios and characteristic variations. This parameter adjustment in the resistive network balances the temperature coefficients, flattening the overall temperature dependence of the reference voltage.
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 corrects temperature-dependent variations, ensuring a more constant reference voltage across a wide temperature range, improving accuracy and stability of the output voltage.
Implementation Method 1
the voltage VBE between the base and emitter of the transistor Q2 has a negative temperature coefficient that decreases with respect to the temperature rise
Implementation Method 2
a voltage having a positive temperature coefficient that increases with respect to temperature rise is generated across the resistor R2
Implementation Method 3
an operational amplifier that differentially amplifies the voltage between the collectors of the transistors Q1 and Q2
Implementation Method 4
The output currents are supplied to a mirror circuit, whose output corrects the output voltage of the Brokaw cell
Data Source
AI summary
A reference voltage generating circuit comprises a pair of variable resistors connected to a pair of bipolar transistors. A differential amplifier amplifies the band gap voltage difference between the bipolar transistors and outputs a reference voltage to an output terminal. An output stage resistor is connected to the output terminal and a resistance dividing circuit. The generating circuit includes temperature compensating circuits that receive tap voltages from resistance dividing circuit and a current proportional to the temperature, then output correction currents. The generating circuit additionally includes a current mirror circuit that outputs a mirror current depending on each correction current. The reference voltage generating circuit thus corrects the temperature dependence of the reference voltage.