Temperature-Coefficient Bias Circuit for Stable 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 in proximity to heat-generating components, and existing solutions often require matching temperature coefficients which can be difficult and inaccurate.
Innovation Solution
A controllable temperature coefficient bias circuit that provides independent control over current levels and temperature coefficients, using a variable with temperature circuit and a proportional-to-absolute-temperature circuit to maintain constant gain by adjusting current ratios through digitally controlled resistance changes, allowing for precise temperature compensation without relying on 'like-kind' devices.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Temperature
If traditional PTAT circuits are used to maintain constant gain over temperature, then temperature compensation is achieved, but manufacturing precision and accuracy are compromised due to difficulty in matching temperature coefficients
Solution Approach 1:
The patent changes the approach from matching temperature coefficients to independently controlling them. The bias circuit generates two separate currents with different temperature coefficients that are summed to create a composite bias current. This allows the temperature coefficient to be controlled by adjusting current ratios rather than by precise component matching, thereby resolving the contradiction between temperature stability and manufacturing precision.
Solution Approach 2:
The bias circuit is segmented into multiple independent current sources, each with its own temperature coefficient characteristics. Instead of relying on a single matched pair of components, the circuit divides the bias current into segments that can be independently adjusted. This segmentation eliminates the need for precise temperature coefficient matching while maintaining temperature compensation.
2Stability of the object's composition
If current levels are adjusted to compensate for temperature variations, then gain stability is improved, but device complexity increases due to additional control mechanisms
Solution Approach 1:
The bias circuit uses a universal approach where a single circuit structure provides both temperature compensation and gain stabilization functions. The same current sources and summing nodes that provide temperature compensation also maintain gain stability across operating conditions. This multi-functionality reduces overall device complexity compared to separate control mechanisms.
3Manufacturing precision
If independent control of current levels and temperature coefficients is implemented, then manufacturing precision is improved, but device complexity increases due to additional control elements
Solution Approach 1:
The patent implements dynamic control where the bias circuit can adjust current ratios in response to operating conditions. The control mechanism dynamically balances the two current sources to achieve the desired temperature coefficient and current level. This dynamic approach provides precise manufacturing control without requiring a large number of static control elements.
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.