LNA Input Impedance Adjustment via Negative Magnetic Coupling
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Solution Overview
Problem
Existing low-noise amplifiers (LNAs) face challenges in achieving optimal input impedance matching with filters, leading to degraded noise figure and filter performance due to negative capacitance effects and thermal noise from resistors, which increase form factor and cost when using off-chip elements.
Innovation Solution
An input impedance adjustment circuit using negative magnetic coupling between inductors and capacitors is employed to cancel the negative capacitance effects, enhancing the real part of the input impedance and improving impedance matching with filters, thereby reducing noise figure and thermal noise.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If traditional LNA input impedance matching is used, then the circuit is simple, but the noise figure degrades due to negative capacitance effects
Solution Approach 1:
An impedance adjustment circuit is introduced as an intermediary between the filter and the LNA. This circuit includes a first inductor coupled to the LNA input node, a second inductor magnetically coupled to the first inductor, and a capacitor coupled to the second inductor, forming a mediating network that compensates for negative capacitance effects without requiring direct modification of the LNA core circuitry.
Solution Approach 2:
The invention changes the electrical parameters of the input impedance by introducing reactive elements (inductors and capacitors) with specific values. The first inductor has inductance L1, the second inductor has inductance L2, and the capacitor has capacitance C, where these parameters are selected to provide the desired impedance transformation and noise figure improvement at the operating frequency.
2Reliability
If resistors are used to adjust input impedance, then impedance matching is achieved, but thermal noise increases and form factor increases
Solution Approach 1:
The invention substitutes resistive impedance adjustment with reactive impedance adjustment using inductors and capacitors. Instead of using resistors that dissipate power and generate thermal noise, the circuit employs magnetic coupling between inductors and capacitive elements to achieve impedance transformation, thereby eliminating thermal noise generation while maintaining impedance matching capability.
3Reliability
If off-chip elements are used to adjust impedance, then impedance matching improves, but form factor and cost increase
Solution Approach 1:
The impedance adjustment circuit is merged with the LNA input stage by coupling the first inductor directly to the input node of the LNA. The magnetic coupling between the first and second inductors allows for compact integration, and the entire circuit can be implemented using on-chip inductors and capacitors, eliminating the need for separate off-chip impedance matching components.
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
The solution effectively increases the real part of the input impedance, improving impedance matching and reducing noise figure, thus enhancing the performance of both the LNA and the filter without increasing form factor or cost.
Implementation Method 1
a second inductor, wherein the second inductor is coupled with the first inductor through negative magnetic coupling
Data Source
AI summary
Aspects of the present disclosure provide a circuit configured to adjust an input impedance of an amplifier such as a low-noise amplifier. In certain aspects, the circuit is coupled to a node, wherein the node is between a first transistor and a second transistor of the amplifier. The circuit may include an inductor and a capacitor coupled in series, wherein the inductor is coupled with one or more load inductors of the amplifier through negative magnetic coupling.