Active Inductor DC Bias for RF Filter Parasitics
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Solution Overview
Problem
Existing radio frequency (RF) filter circuits in dual conversion tuners face performance issues due to parasitic attributes from DC biasing circuits, which affect the filter's frequency response and impedance, leading to interference from image and spurious frequencies.
Innovation Solution
The implementation of an active inductor configuration as a DC current path circuitry that absorbs parasitic attributes, using a transistor-based active inductor to provide a low impedance at DC frequencies and high impedance at RF frequencies, thereby eliminating the adverse effects on the filter's performance without increasing the circuit's size.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a traditional DC biasing circuit with high inductance is used, then the filter achieves desired frequency response, but the circuit size increases and parasitic attributes interfere with filter performance
Solution Approach 1:
The patent replaces the traditional passive inductor-based DC biasing circuit with an active inductor implementation using a transistor (M1) and associated components. This substitution eliminates the need for large physical inductors while maintaining the DC biasing function, thereby reducing circuit area while preserving filter frequency response characteristics.
Solution Approach 2:
The patent changes the operational parameters by using an active transistor circuit to simulate inductor behavior at DC frequencies while presenting high impedance at RF frequencies. This parameter change allows the circuit to achieve the same electrical function with significantly reduced physical dimensions.
2Reliability
If traditional DC biasing circuits are used, then the filter provides DC current path, but parasitic attributes from the biasing circuit interfere with the filter's frequency response and impedance
Solution Approach 1:
The patent extracts the harmful parasitic attributes from the traditional DC biasing circuit by separating the DC current path function from the RF signal path. The active inductor configuration allows DC current to flow through the transistor while presenting high impedance to RF frequencies, effectively removing parasitic interference from the filter's frequency response.
Solution Approach 2:
The transistor-based active inductor acts as an intermediary element that couples the DC biasing network to the filter circuit while isolating the RF signal from parasitic effects. This intermediary provides the necessary DC current path while preventing parasitic attributes from affecting the filter's impedance and frequency response.
3Measurement precision
If high inductance DC biasing circuits are used, then the filter achieves precise center frequency control, but the circuit complexity and area increase
Solution Approach 1:
The patent replaces complex passive inductor networks with a simplified active transistor circuit that achieves the same center frequency control function. The active inductor configuration using transistor M1 provides precise frequency control through manageable component values while reducing overall circuit complexity.
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
This solution allows for precise center frequency control and high Q-factor filtering with reduced area requirements, minimizing interference from unwanted signals and maintaining the filter's performance without the drawbacks of traditional high inductance DC biasing circuits.
Implementation Method 1
using a transistor-based active inductor to provide a low impedance at DC frequencies and high impedance at RF frequencies
Implementation Method 2
The implementation of an active inductor configuration as a DC current path circuitry that absorbs parasitic attributes
Data Source
AI summary
Systems and methods which provide DC current path circuitry, such as for providing a DC bias, in association with a filter circuit such that parasitic attributes of the DC current path circuitry combines with the filter component attributes are shown. According to embodiments, the parasitic attributes of the DC current path circuitry components are added into the associated filter circuit network design. A parasitic capacitance of the DC current path circuitry may, for example, be aggregated with a capacitor of the filter circuit to eliminate or mitigate the effect of the presence of the DC current path circuitry on the associated filter frequency response. Embodiments implement an active inductor configuration for providing a DC current path in association with a filter circuit. An active inductor of embodiments is provided using a transistor, appropriately biased to actively exhibit low impedance at DC and high impedance at RF frequencies.