Negative Impedance Circuit Topology for Rail-to-Rail Operation
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Solution Overview
Problem
Existing negative impedance circuits have limited operating ranges due to the requirement for operational amplifiers (op-amps) to have a gain greater than unity, causing saturation when the voltage approaches the supply rails, resulting in the circuit behaving as a positive resistance rather than maintaining negative impedance.
Innovation Solution
The development of techniques that allow negative impedance circuits to operate to their power supply rails by generating currents in response to differential voltage signals, mirroring these currents back to the input terminals, and controlling the circuit to operate about a common-mode voltage, using configurations such as parallel resistor-capacitor circuits with matched or unmatched impedance magnitudes to achieve desired impedance characteristics.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If operational amplifiers are used with gain greater than unity to develop negative impedance, then negative impedance is achieved, but the circuit has limited operating range and saturates when voltage approaches supply rails
Solution Approach 1:
The circuit is divided into multiple operational amplifiers with specific configurations. The first op-amp is configured with unity gain to avoid saturation, while a second op-amp provides the necessary gain. This segmentation allows the circuit to maintain negative impedance behavior across a wider voltage range without saturation, resolving the contradiction between reliability of negative impedance maintenance and adaptability of operating range.
2Reliability
If op-amp gain is increased to maintain negative impedance, then negative impedance behavior is preserved, but the op-amp saturates near supply rails causing the circuit to become positive resistance
Solution Approach 1:
A second operational amplifier is introduced as an intermediary element. The first op-amp operates at unity gain to handle the voltage signal without saturation, while the second op-amp amplifies the feedback signal to maintain the negative impedance characteristic. This intermediary structure allows the circuit to operate effectively near supply rails while preserving negative impedance behavior, resolving the contradiction between reliability of negative impedance behavior and ease of operation across voltage range.
Data Source
AI summary
Techniques to develop negative impedance circuits that may operate to their power supply rails. The techniques may include generating currents in response to voltage signals presented at respective input terminals of a negative impedance circuit. The voltage signals may be differential signals. The generated currents may be driven through a common impedance within the negative impedance circuit. The currents flowing through the common impedance may be mirrored back to the input terminals of the negative impedance circuit. The negative impedance circuit may be controlled to operate about a common-mode voltage for the circuit.