Transferred Impedance Filter Clocking for Odd-Harmonic Rejection
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Solution Overview
Problem
Existing signal filters, particularly in wireless communication equipment, face limitations in harmonic rejection and attenuation around odd harmonics of the local oscillator frequency, leading to inadequate filtering performance for applications like wireless local area networks in cellular transceivers.
Innovation Solution
A signal filter comprising two 4-differential-path transferred impedance filters (TIFs) coupled in parallel, each clocked with non-overlapping clock signals having a duty cycle in the range of 16.75% to 25%, with the second TIF's clock phases delayed by 45 degrees relative to the first TIF's phases, enabling reduced harmonic folding and improved attenuation without increasing the oscillator frequency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If the number of phases in TIF is increased to 6 or 8 paths to improve harmonic rejection, then harmonic rejection capability is improved, but the maximum VCO frequency required for generating the LO signal increases significantly
Solution Approach 1:
The patent changes the duty cycle parameter of the clock signals to a specific range (16.75% to 25%) and optimizes the phase shift to 45 degrees between the two TIFs. This parameter optimization allows achieving improved harmonic rejection with a 4-path TIF configuration, avoiding the need to increase to 6 or 8 paths which would require higher VCO frequencies.
2Manufacturing precision
If the switching duty cycle is reduced to improve bandpass frequency selectivity, then frequency selectivity is improved, but attenuation at odd harmonics of the LO signal is severely degraded
Solution Approach 1:
The patent optimizes the duty cycle parameter to a specific range (16.75% to 25%) rather than using extremely short duty cycles. This optimized parameter range achieves improved bandpass frequency selectivity while maintaining adequate attenuation at odd harmonics of the LO signal, resolving the trade-off between these two performance aspects.
Solution Approach 2:
The patent combines two 4-path TIFs in parallel with complementary clock phases (45 degrees shifted). This merging approach provides frequency selectivity through the TIF structure while the parallel combination with phase diversity improves harmonic attenuation by distributing the switching activity across different phases.
3Object-affected harmful factors
If shorter switch on-time is used to improve filtering at odd harmonics, then filtering at odd harmonics is improved, but losses in the desired passband increase
Solution Approach 1:
The patent optimizes the duty cycle to a moderate range (16.75% to 25%) rather than using extremely short on-times. This parameter optimization ensures sufficient filtering at odd harmonics while maintaining adequate switch on-time to minimize resistive losses in the passband, balancing harmonic rejection with passband efficiency.
Data Source
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AI summary
A signal filter (100) comprises a first transferred impedance filter, TIF, (TIFA) having four differential signal paths (PA,1, PA,2, PA,3, PA,4) and a second TIF (TIFB) having four differential signal paths (PB,1, PB,2, PB,3, PB,4). A first differential signal port of the first TIF (32A) is coupled to a first differential signal port of the second TIF (32B). A first clock generator (12A) is arranged to provide first-TIF clock signals (CLKA,l+, CLKA,Q+, CLKA,l-, CLKA,Q-) having four non-overlapping phases for selecting the respective first-TIF differential signal paths (PA,1, PA,2, PA,3, PA,4), and a second clock generator (12B) is arranged to provide second-TIF clock signals (CLKB,l+, CLKB,Q+, CLKB,l-, CLKB,Q-) having four non-overlapping phases for selecting the respective second-TIF differential signal paths (PB,1, PB,2, PB,3, PB,4). The phases of the second-TIF clock signals (CLKB,l+, CLKB,Q+, CLKB,l-, CLKB,Q-) are equal to the phases of the first-TIF clock signals (CLKA,l+, CLKA,Q+, CLKA,l-, CLKA,Q-) delayed by 45 degrees.