Differential Amplifier Gain Compensation Using CMOS Feedback
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Solution Overview
Problem
Amplifier stages using MOSFETs and CMOS transistors experience gain reduction with increasing temperature, leading to variable power output and linearity issues, and existing solutions like programmable current amplifiers increase manufacturing costs and have accuracy limitations.
Innovation Solution
A differential amplifier stage with a temperature compensation circuit using two CMOS transistors that provide a feedback resistance to maintain constant gain, where the CMOS transistors control the gain through a temperature-dependent voltage, minimizing temperature dependence.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a programmable current amplifier is used to compensate for temperature dependence, then the gain can be maintained across temperatures, but the manufacturing costs increase and accuracy is limited due to discrete programming steps
Solution Approach 1:
The patent implements a feedback mechanism where a feedback transistor connects the output to the input of the amplifier stage. This feedback loop automatically adjusts the gain by utilizing the temperature-dependent characteristics of the feedback transistor to counteract the temperature-induced gain variations in the main amplifying transistors, eliminating the need for external programmable components
Solution Approach 2:
The amplifier stage uses its own output signal and inherent transistor characteristics to generate the compensation effect. The feedback transistor leverages the same temperature-dependent behavior as the main transistors to automatically regulate gain without requiring external control circuits or programmable elements, making the system self-regulating
2Reliability
If resistors and diodes are added to compensate for temperature dependence, then worst-case temperatures can be handled, but the device complexity and manufacturing cost increase
Solution Approach 1:
The feedback transistor serves multiple functions simultaneously: it provides the primary feedback for gain control, acts as a temperature compensation element, and contributes to the overall amplification process. This multi-functionality eliminates the need for separate compensation components like resistors and diodes, reducing circuit complexity while maintaining temperature range performance
Solution Approach 2:
The patent exploits the natural parameter changes (temperature-dependent characteristics) of the feedback transistor to achieve compensation. By carefully selecting the transistor dimensions and biasing conditions, the feedback transistor's parameters change with temperature in a manner that counteracts the gain variations of the main amplifying transistors, providing temperature compensation without additional components
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 ensures a constant small signal gain for the amplifier stage across varying temperatures, reducing manufacturing costs and complexity while maintaining high linearity, by using a simple and efficient temperature-controlled feedback mechanism.
Implementation Method 1
The CMOS transistors of the temperature compensation circuit will control the gain of the amplifier stage by means of a controlled feedback resistance. A temperature dependent voltage of the temperature compensation circuit will set the linearity of the gain so that the gain of the amplifier stage has minimum dependence on temperature.
Data Source
AI summary
The invention relates to an differential amplifier circuit comprising an amplifier stage comprising a first and a second transistor, the gates of which are connected to differential input terminals of the amplifier stage. The differential amplifier further comprises a temperature compensation circuit comprising a third and fourth transistor. The third transistor is connected to the source of the first transistor and the fourth transistor is connected to the source of the second transistor. Further, the temperature compensation circuit comprises a constant current source connected to the respective sources of the third and fourth transistors. Thereby the temperature compensation circuit is arranged to provide a feedback resistance in dependence on the operating temperature so as to compensate for variations of the resistance of the first and second transistors.