Passive Mixer LLC Filter for Wideband Linearity and Harmonic Rejection
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Solution Overview
Problem
Existing RFIC transceiving circuits face challenges in achieving high linearity and wide bandwidth due to low impedance and high power consumption, especially in high-frequency bands, which is exacerbated by the limitations of active mixer structures.
Innovation Solution
A passive mixer structure with an LLC filter is employed, featuring a configuration of inductors and a capacitor to provide high impedance and reject 3rd harmonic frequencies, thereby improving power consumption and impedance characteristics in higher frequency bands.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If active mixer structures are used in high-frequency bands, then mixing function is achieved, but power consumption increases and linearity decreases
Solution Approach 1:
The patent replaces the active mixer structure with a passive mixer structure, substituting active devices (transistors) with passive devices (inductors, capacitors, resistors). This substitution eliminates the high power consumption and linearity issues inherent in active mixer structures operating at high frequencies, while maintaining the essential mixing function through passive impedance transformation.
Solution Approach 2:
The patent changes the operating parameters by designing the passive mixer with specific impedance values (e.g., 50Ω differential output impedance) and using an LLC filter with tuned inductance and capacitance values to achieve optimal performance at the target frequency. This parameter optimization enables the passive mixer to achieve both low power consumption and high linearity simultaneously.
2Power
If passive mixer structure is used, then power consumption decreases, but impedance matching becomes difficult and bandwidth is limited
Solution Approach 1:
The patent introduces an LLC filter as an intermediary component between the passive mixer and the subsequent amplifier stage. This filter serves as a mediator that performs impedance transformation and frequency selection, enabling the passive mixer to achieve both low power consumption and wide bandwidth by properly matching impedances across different stages while filtering out unwanted harmonics.
Solution Approach 2:
The LLC filter performs multiple functions simultaneously: impedance matching, frequency selection, and harmonic rejection. This multi-functionality allows the passive mixer to achieve wide bandwidth support while maintaining low power consumption, as the single filter structure addresses multiple performance requirements that would otherwise require separate components.
3Adaptability or versatility
If output impedance is increased to support wide bandwidth, then bandwidth increases, but 3rd harmonic rejection becomes insufficient
Solution Approach 1:
The patent converts the harmful 3rd harmonic distortion into a beneficial filtering opportunity by designing the LLC filter with a resonant frequency that specifically targets and rejects the 3rd harmonic. The filter's inductance and capacitance values are tuned so that the 3rd harmonic frequency coincides with the filter's stopband, transforming the harmonic distortion problem into an effective frequency selection mechanism that maintains wide bandwidth while achieving superior harmonic rejection.
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 reduces power consumption and enhances the 3rd harmonic rejection ratio, achieving a high impedance at the operating frequency while maintaining low impedance at harmonic frequencies, thus supporting wider bandwidths and reducing physical size.
Implementation Method 1
a first inductor connecting a first node of the differential output of the transmission mixer to a first intermediate node, a second inductor connecting a second node of the differential output of the transmission mixer to a second intermediate node, a third inductor connecting the first intermediate node to the second intermediate node
Implementation Method 2
a capacitor in parallel with the third inductor
Implementation Method 3
LLC filter electrically connected to a differential output of the transmission mixer and a differential input of the driving amplifier
Data Source
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AI summary
Disclosed is a transmission radio frequency (RF) circuit including a transmission mixer configured to receive an intermediate frequency (IF) signal and up-convert the IF signal into an RF signal, a driving amplifier configured to amplify the RF signal, and an LLC filter electrically connected to a differential output of the transmission mixer and a differential input of the driving amplifier, the LLC filter comprising a first inductor connecting a first node of the differential output of the transmission mixer to a first intermediate node, a second inductor connecting a second node of the differential output of the transmission mixer to a second intermediate node, a third inductor connecting the first intermediate node to the second intermediate node, and a capacitor in parallel with the third inductor.