Negative gm Circuit Enhances LC Filter Q Factor
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Solution Overview
Problem
In frequency division duplex communication systems, achieving high isolation between transmitter and receiver is challenging, especially when the frequency difference between the transmit and receive signals is small, leading to complex filter designs and performance issues with integrated LC notch filters due to their low Q factor and increased noise, power consumption, and complexity.
Innovation Solution
A negative resistance circuit is synthesized using first and second active devices, with an inductor integrated within the circuit, allowing for improved performance in amplifiers and frequency division duplex systems by enhancing the quality factor of LC filters without significant noise penalty, using a configuration of transistors and capacitors that reduces noise and power consumption.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If external filters are used between low noise amplifier and mixer, then blocking signal rejection is improved, but device complexity and pin requirements increase
Solution Approach 1:
The patent combines the filter function with the low noise amplifier by integrating a resonant circuit directly into the amplifier circuit. The amplifier and filter share common components (transistors, inductors, capacitors), eliminating the need for separate external filter devices and reducing pin requirements while maintaining blocking signal rejection capability.
Solution Approach 2:
The circuit implements multi-functionality by making the low noise amplifier also serve as the filter. The same transistors and reactive components provide both amplification and frequency-selective filtering functions, reducing overall device complexity and component count.
2Device complexity
If integrated LC notch filters are used, then device integration is improved, but quality factor and performance deteriorate due to low Q factor of spiral inductors
Solution Approach 1:
The patent changes the circuit configuration from a simple parallel LC notch filter to a resonant circuit with active feedback. By using transistors in a regenerative configuration with the LC tank, the circuit achieves a high effective Q factor that overcomes the inherent low Q of integrated spiral inductors, while maintaining full integration.
Solution Approach 2:
The circuit employs positive feedback through the transistor configuration where the output of the amplifying stage is fed back to the input through the resonant tank. This feedback mechanism compensates for energy losses in the inductor and enhances the quality factor of the integrated filter.
3Object-affected harmful factors
If higher order filters are used to achieve large isolation, then isolation performance is improved, but filter design complexity increases
Solution Approach 1:
The patent achieves wideband rejection through a continuous resonant response rather than discrete notches. The regenerative resonant circuit provides sustained oscillation and energy storage in the LC tank, creating a broad rejection band that maintains isolation performance without requiring multiple high-order filter sections.
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 provides improved filter performance with reduced noise and power consumption, achieving better isolation and rejection of interfering signals, while maintaining sensitivity, and requires fewer components and less complexity compared to traditional colpitts cell implementations.
Implementation Method 1
first and second devices interacting with each other such that the circuit synthesises a negative resistance
Implementation Method 2
an inductor integrated within the circuit
Implementation Method 3
integrated LC resonant circuits
Data Source
AI summary
A circuit for synthesising a negative resistance, comprising first and second active devices, the first device having a control terminal connected to a first node, and the second device having a current flow terminal connected to the first node, and the first and second devices interacting with each other such that the circuit synthesises a negative resistance.