Negative Impedance Circuit Using Current-Mirror Feedback
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Existing negative impedance circuits, particularly in read interfaces for Piezoelectric Micro-machined Ultrasonic Transducers (PMUTs), face limitations due to high resistance ratios in the feedback path, which restrict input signal dynamics and lead to undesirable low input impedance.
Innovation Solution
The implementation of a negative impedance circuit using a differential stage with a combination of positive and negative feedback paths, where the negative feedback path is coupled without voltage amplification and includes a reference impedance, allowing for a high negative capacitance without amplifying the input-output voltage, thereby enhancing signal dynamics by modifying the input impedance through a negative impedance ratio.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If conventional negative impedance circuits use high resistance ratios in the feedback path to achieve negative capacitance, then negative capacitance is implemented, but input signal dynamics are limited and input impedance becomes undesirably low
Solution Approach 1:
The patent changes the feedback mechanism from voltage-based to current-based by using a current mirror circuit. This parameter change allows the negative capacitance to be achieved without relying on high resistance ratios, thereby maintaining good input signal dynamics and avoiding the limitation of low input impedance while still achieving the desired negative capacitance effect.
2Power
If voltage amplification is used in the feedback path to enhance signal, then signal gain is improved, but the denominator in the impedance ratio increases which limits input signal dynamics
Solution Approach 1:
The patent replaces the voltage amplification mechanism with a current mirror mechanism. Instead of using voltage amplification that increases the denominator in the impedance ratio, the current mirror directly replicates and inverts the input current, achieving signal enhancement without the adverse effect on input signal dynamics caused by voltage amplification.
Data Source
AI summary
A negative impedance circuit includes: a differential circuit stage; a positive feedback path from an output of the differential circuit stage to a first input of the differential circuit stage; and a negative feedback path from the output of the differential circuit stage to a second input of the differential circuit stage. The negative feedback path includes a first transistor, and a unitary gain path from the output of the differential circuit stage to the second input of the differential circuit stage, the unitary gain path coupled to ground via a reference impedance. The positive feedback path includes a second transistor. The first and second transistors are coupled in a current mirror arrangement and have respective control electrodes configured to be driven by the output of the differential circuit stage, where the negative impedance circuit causes a negative impedance at the first input of the differential circuit stage.