Controllable Bias Circuit for Temperature-Stable Amplifier Gain
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Existing amplifier circuits face challenges in maintaining constant gain over a broad temperature range, particularly when using field effect transistors (FETs), as the gain varies with temperature due to transconductance changes, and it is difficult to offset these variations without using 'like-kind' devices, especially in environments with rapid switching and silicon-on-insulator (SOI) FETs.
Innovation Solution
A controllable temperature coefficient bias (CTCB) circuit is introduced, comprising a variable with temperature (VWT) circuit and a control circuit with two current control elements having controllable resistances, allowing independent control of current levels and temperature coefficient slopes, using digital signals to adjust the bias current to compensate for temperature effects.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Stability of the object's composition
If a proportional-to-absolute-temperature (PTAT) circuit is used to maintain constant gain, then the gain stability over temperature is improved, but the device complexity increases and requires matched 'like-kind' devices
Solution Approach 1:
The patent changes the temperature coefficient parameter of the bias current from fixed (as in traditional PTAT circuits) to variable and controllable. By adjusting the temperature coefficient parameter, the circuit can compensate for transistor transconductance variations without requiring complex matched device pairs, thus maintaining gain stability while reducing circuit complexity
Solution Approach 2:
The patent introduces dynamic control of the bias current's temperature coefficient through a control circuit that can adjust the temperature compensation characteristic in real-time. This dynamic adjustment allows the amplifier to maintain constant gain across temperature variations without the static limitations and matching requirements of traditional PTAT circuits
2Device complexity
If traditional bias circuits are used, then the device simplicity is maintained, but the gain varies with temperature
Solution Approach 1:
The patent introduces a control circuit as an intermediary between the power supply and the amplifier bias current. This control circuit generates a bias current with a controllable temperature coefficient that compensates for transistor transconductance variations, thereby maintaining constant gain while keeping the overall circuit relatively simple and avoiding the need for complex matched device structures
3Stability of the object's composition
If 'like-kind' devices are used for temperature compensation, then the gain stability is improved, but the manufacturing difficulty and cost increase
Solution Approach 1:
The patent changes the approach from using matched 'like-kind' devices to using a controllable temperature coefficient parameter in the bias current. This parameter-based approach achieves the same gain stability effect without requiring precise device matching, thereby simplifying the manufacturing process and reducing costs associated with selecting and matching specific transistor pairs
4Productivity
If rapid switching operation is implemented, then the productivity is improved, but the gain stability over temperature becomes more difficult to maintain
Solution Approach 1:
The control circuit acts as an intermediary that can rapidly adjust the bias current's temperature coefficient in response to temperature changes during fast switching operations. This dynamic compensation mechanism maintains gain stability even during rapid transitions, allowing the amplifier to operate at high speeds without sacrificing temperature compensation effectiveness
Data Source
AI summary
A controllable temperature coefficient bias (CTCB) circuit is disclosed. The CTCB circuit can provide a bias to an amplifier. The CTCB circuit includes a variable with temperature (VWT) circuit having a reference circuit and a control circuit. The control circuit has a control output, a first current control element and a second current control element. Each current control element has a “controllable” resistance. One of the two current control elements may have a relatively high temperature coefficient and another a relatively low temperature coefficient. A controllable resistance of one of the current control elements increases when the controllable resistance of the other current control element decreases. However, the “total resistance” of the current control circuit remains constant with a constant temperature. The VWT circuit has an output with a temperature coefficient that is determined by the relative amount of current that flows through each current control element of the control circuit. A Current Digital to Analog Converter (IDAC) scales the output of the VWT and provides the scaled output to an amplifier bias input.