Negative Impedance Circuit With Constant-Gm Biasing for Amplifier Noise
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Operational amplifiers face challenges in reducing internal noise in output signals without increasing power dissipation, and existing negative resistance circuits are prone to instability due to variations in component values caused by process voltage or temperature changes.
Innovation Solution
The implementation of cross-coupled transistor circuits biased with constant-Gm biasing, which provide a small signal negative resistance value and are insensitive to process voltage or temperature variations, maintaining stability and effectively canceling internal noise.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If conventional negative resistance circuits are used to reduce operational amplifier noise, then noise reduction is achieved, but circuit stability deteriorates due to component value variations from process voltage or temperature changes
Solution Approach 1:
The patent applies parameter changes by using constant-Gm biasing to maintain the transconductance parameter of cross-coupled transistors stable across process voltage and temperature variations. This ensures the negative resistance value remains constant, stabilizing the circuit while maintaining noise reduction effectiveness.
Solution Approach 2:
The patent implements feedback through constant-Gm biasing circuits that continuously monitor and adjust the bias conditions of cross-coupled transistors. This feedback mechanism compensates for environmental variations, maintaining stable negative resistance values and preventing circuit instability.
2Use of energy by moving object
If operational amplifier power dissipation is reduced, then energy efficiency is improved, but internal noise in output signals increases
Solution Approach 1:
The patent introduces cross-coupled transistors configured as a negative resistance circuit as an intermediary element connected to the operational amplifier. This intermediary actively generates negative resistance to cancel noise, allowing the operational amplifier to operate at lower power while maintaining low noise output through the compensating action of the negative resistance circuit.
Data Source
Figure 1
Figure 2
Figure 3
AI summary
A circuit includes a first operational amplifier having an inverting input and a noninverting input, and a negative resistance circuit connected to the inverting input of the operational amplifier. The negative resistance circuit includes a second operational amplifier, a current source controlled by the second operational amplifier, and a crosscoupled transistor circuit having at least one transistor biased by a current produced by the current source.