Integrated LNB Downconversion Circuit for Image Rejection
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Solution Overview
Problem
Traditional LNB frequency down conversion systems face issues with frequency stability due to temperature drift, occupy valuable PCB space with band-pass filters, and are cumbersome for manufacturing and debugging due to numerous discrete components.
Innovation Solution
An integrated LNB frequency down conversion chip incorporating a pre-amplifier, quadrature voltage-controlled oscillator, quadrature frequency mixer, In-phase/Quadrature intermediate frequency amplifier, and polyphase filter to transform single-ended signals into differential signals, produce quadrature local oscillations, and eliminate mirror image signals, thereby enhancing noise suppression and reducing component count.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If discrete components are used for LNB design, then the system is easier to manufacture with individual components, but the device complexity increases and PCB area is occupied by band-pass filters
Solution Approach 1:
The patent integrates multiple discrete components including the band-pass filter, frequency mixer, and amplifier into a single integrated circuit chip. This merging eliminates the need for separate discrete components and their interconnections, thereby reducing device complexity while maintaining ease of manufacture through standardized chip production processes
Solution Approach 2:
The integrated circuit chip performs multiple functions simultaneously: frequency conversion, signal amplification, and mirror image suppression through the integrated band-pass filter. This multi-functionality reduces the overall component count and simplifies the system architecture while maintaining ease of manufacture
2Reliability
If passive band-pass filter is used to filter out-of-band signals, then the noise performance is improved, but the PCB area is occupied and manufacturing complexity increases
Solution Approach 1:
The band-pass filter function is integrated into the same chip as the frequency mixer and amplifier circuits. This integration eliminates the need for separate PCB-mounted passive filters, freeing up valuable PCB area while maintaining the noise performance benefits of filtering out-of-band and mirror image signals
Solution Approach 2:
The band-pass filter is nested within the integrated circuit chip structure, with the filter circuits embedded alongside the mixer and amplifier circuits. This nesting approach allows the filter functionality to be contained within the chip footprint rather than occupying separate PCB space
3Device complexity
If Dielectric Resonator Oscillator is used for frequency generation, then the circuit is simpler, but the frequency stability deteriorates due to temperature drift
Solution Approach 1:
The patent employs a temperature-compensated crystal oscillator instead of a simple dielectric resonator oscillator. By changing the oscillator type to one with inherent temperature compensation capabilities, the system maintains frequency stability across temperature variations while keeping the circuit design relatively simple through the use of standard compensated oscillator circuits
Data Source
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AI summary
The present invention disclosed a type of LNB frequency down conversion integrated circuit. The present invention frequency-down-converts the RF signal with the Quadrature local oscillation signal (LO) and Quadrature Mixer. Then the 90 degree phase-shifting of the quadrature intermediate frequency (IF) signal after mixed is done by the use of passive Polyphase filter. The present invention further disclosed a LNB frequency down conversion chip, a LNB frequency down circuit adopting the LNB frequency down conversion chip circuit and a method of LBN frequency down. The invention ensures the elimination of the mirror image signal and the realization of the mirror image suppression function.