Programmable Gain INA Frontend With V2I-Driven Resistor Network
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Solution Overview
Problem
Current instrument amplifiers (INAs) with current-feedback architecture face limitations in programmable gain due to signal-dependent current flowing through the entire gain resistor network, leading to large voltages across resistors and a restricted operating signal range.
Innovation Solution
Incorporating a voltage-to-current converter (V2I) that drives the gain resistor network via a switch, allowing unused resistors to receive little current and maintaining a near-constant bandwidth across all gain values, while the V2I tracks differential input voltage and provides current to specific nodes in the gain resistor network for programmable gain.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If a current-feedback architecture INA with programmable gain is used, then gain can be adjusted via an internal resistor network, but signal-dependent current flows through the entire gain resistor network causing large voltages across resistors and restricting the operating signal range
Solution Approach 1:
The gain resistor network is segmented into multiple sections with tap points, allowing the V2I to inject current at specific locations rather than forcing signal-dependent current through the entire network. This segmentation enables selective activation of resistor portions based on desired gain, preventing large voltage drops across unused resistors and expanding the operating signal range.
Solution Approach 2:
A voltage-to-current converter (V2I) is introduced as an intermediary component that converts the differential input voltage to a current and injects it at specific tap points in the gain resistor network. This intermediary enables programmable gain control without requiring signal-dependent current to flow through the entire resistor network, thereby eliminating the voltage drop limitation and expanding the operating signal range.
2Power
If the gain resistor network is configured for high gain, then amplification is increased, but bandwidth decreases due to signal-dependent current flow
Solution Approach 1:
The V2I acts as an intermediary that provides the necessary current for high gain amplification without requiring signal-dependent current to traverse the entire gain resistor network. By injecting current at optimally selected tap points, the system achieves high amplification gain while maintaining wide bandwidth, effectively decoupling the gain-bandwidth tradeoff that plagues conventional current-feedback INAs.
Solution Approach 2:
The system dynamically selects which tap points in the gain resistor network to activate based on the desired gain setting. This dynamic configuration allows the system to optimize the current injection location for each gain level, maintaining wide bandwidth across all gain settings from low to high, rather than being constrained by a fixed signal-dependent current path.
3Adaptability or versatility
If the operating signal range is expanded, then larger input signals can be processed, but signal-dependent current increases causing larger voltages across the gain resistor network
Solution Approach 1:
The V2I serves as an intermediary that handles the conversion of large input signals to current, preventing large signal-dependent current from flowing through the gain resistor network. By injecting the converted current at specific tap points, the system can process larger input signals within an expanded operating range without generating harmful large voltages across the resistor network.
Solution Approach 2:
The harmful signal-dependent current is extracted from the gain resistor network path by using the V2I to provide the necessary current independently. This extraction allows the gain resistor network to operate with controlled, non-signal-dependent current, enabling expanded operating signal range without the penalty of large voltages developing across the resistors.
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
This approach enables INAs with current-feedback architecture to achieve programmable gain without signal-dependent current through the entire resistor network, maintaining high bandwidth across various gain settings, thus expanding the operating signal range and allowing for precise amplification.
Implementation Method 1
generating a current in the voltage to current converter proportional to a difference between the first input signal and the second input signal
Data Source
AI summary
A system includes an instrumentation amplifier (INA) including a first transistor coupled to a first input node, and a second transistor coupled to a second input node. The INA also includes a resistor coupled between the first transistor and the second transistor. The INA includes a gain resistor network coupled to the resistor and to the first and second transistors, where the gain resistor network includes two or more gain resistors. The system also includes a voltage to current converter, where the voltage to current converter is coupled to the resistor and the gain resistor network.