Temperature-Coefficient Bias Circuit for Constant Amplifier Gain
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Solution Overview
Problem
Electrical amplifiers face challenges in maintaining constant gain over a broad temperature range due to variations in transconductance of field effect transistors, especially when operating in uncontrolled environments or with components that generate heat, making it difficult to offset these variations without using 'like-kind' devices which can be inaccurate or inefficient.
Innovation Solution
A controllable temperature coefficient bias circuit that provides independent control over current levels and temperature coefficients, using a combination of current digital-to-analog converters and proportional-to-absolute-temperature circuits to maintain constant gain by adjusting the relative contributions of currents with different temperature coefficients, allowing for precise temperature compensation without relying on 'like-kind' devices.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If traditional PTAT circuits using like-kind devices are used to maintain constant gain, then temperature compensation is achieved, but manufacturing precision and accuracy are compromised due to device matching limitations
Solution Approach 1:
The patent changes the fundamental parameter approach from relying on device matching characteristics to using independently controllable current parameters with specific temperature coefficients. By controlling the ratio and temperature coefficients of currents in parallel branches rather than relying on matched device parameters, the system achieves temperature compensation without the manufacturing precision limitations of like-kind device matching.
Solution Approach 2:
The bias circuit is segmented into multiple independent parallel branches, each with controllable current sources and adjustable resistance elements. This segmentation allows independent control of each branch's temperature coefficient, enabling precise adjustment of the overall bias temperature coefficient without requiring matching between segments, thus resolving the contradiction between reliability and manufacturing precision.
2Device complexity
If fixed bias circuits are used, then circuit simplicity is maintained, but adaptability to different temperature conditions and performance requirements is reduced
Solution Approach 1:
The patent transforms the static fixed bias circuit into a dynamic adjustable circuit by incorporating digitally controllable current sources and resistance elements. The bias circuit can dynamically adjust its temperature coefficient and current levels through digital control signals, providing adaptability to different temperature conditions and performance requirements while maintaining a relatively simple overall structure through integrated control.
Solution Approach 2:
The bias circuit is designed with universal functionality to serve multiple purposes: it can provide temperature compensation, adjust bias current levels, and adapt to different operating conditions through digital control. The same circuit structure can be configured for different temperature coefficients by changing control parameters rather than requiring different hardware configurations, achieving versatility without proportionally increasing complexity.
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 maintains constant amplifier gain over varying temperatures by adjusting the temperature coefficient of the bias current, ensuring accurate and rapid stabilization of the amplifier bias, even in environments with rapid switching and using silicon-on-insulator FETs, which can be challenging for traditional methods.
Implementation Method 1
a current I1 flows through the transistor 106 and a current I2 flows through the FET 110. The currents I1 and I2 change over temperature in order to maintain a constant gm for the FET 108
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.