Frequency-Translated Notch Filter for SAW-Less RF Interference Rejection
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Solution Overview
Problem
Current RF receiver designs face challenges in attenuating large out-of-band interferers on semiconductor substrates, particularly in wideband applications, due to the limitations of silicon-based inductors and the need for high-quality factor filters that are not amenable to monolithic integration.
Innovation Solution
The implementation of frequency translated notch filters (FTNFs) on semiconductor substrates, which use a passive mixer and baseband impedance to create a high-Q band-stop filter, effectively attenuating out-of-band interferers by translating the impedance to a higher frequency, thereby providing a high-impedance path for desired signals and a low-impedance path for interferers.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If SAW filters are used to provide high Q-factor for attenuating out-of-band interferers, then the attenuation performance is improved, but the filter is not amenable to monolithic integration on semiconductor substrate
Solution Approach 1:
The patent replaces the mechanical-resonant SAW filter with an electrical circuit implementation consisting of a passive mixer and baseband impedance network. The mixer translates the baseband notching impedance to the RF frequency domain, achieving high-Q filtering without mechanical components. This substitution enables monolithic integration while maintaining attenuation performance.
Solution Approach 2:
The patent changes the operating parameters by using a passive mixer to translate impedance from baseband to RF frequency. By adjusting the mixer's local oscillator frequency and the baseband impedance values, the filter's center frequency and Q-factor can be tuned without changing the physical structure, enabling flexible design on semiconductor substrates.
2Reliability
If SAW filters are used to provide high Q-factor, then the quality factor is improved, but the insertion loss increases by 1-2 dB
Solution Approach 1:
The electrical mixer-based filter replaces the mechanical SAW filter, eliminating the inherent 1-2 dB insertion loss of SAW devices. The passive mixer introduces minimal loss while the baseband impedance network can be designed to have very low insertion loss at the notching frequency, improving overall signal transmission.
3Reliability
If SAW filters are used for out-of-band interferer attenuation, then the filter performance is improved, but the cost and circuit board area increase
Solution Approach 1:
The patent merges the filter function with the existing RF receiver circuitry by using the passive mixer (already present for frequency conversion) and adding a baseband impedance network. This integration eliminates the need for separate SAW filter components, reducing board area and overall system cost while maintaining filter performance.
Solution Approach 2:
The passive mixer serves dual functions: frequency conversion (its primary role) and impedance translation for filtering (the added function). This multi-functionality eliminates the need for dedicated SAW filters, reducing component count, board area, and cost while achieving the required out-of-band 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
This solution enables efficient attenuation of out-of-band interferers, reducing noise and improving sensitivity in RF receivers, while allowing for monolithic integration and wideband applications without the need for mechanically-resonant SAW filters.
Implementation Method 1
a passive mixer and a baseband impedance, the passive mixer being configured to translate the baseband impedance to a higher frequency
Data Source
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Figure 2A
AI summary
Embodiments of a SAW-less RF receiver front-end (100) that includes a frequency translated notch filter (FTNF) are presented. An FTNF (400) includes a passive mixer (410) and a baseband impedance (420). The baseband impedance (420) includes capacitors (CBB1-CBB4) that form a low-Q band-stop filter. The passive mixer (410) is configured to translate the baseband impedance (420) to a higher frequency. The translated baseband impedance (420) forms a high-Q notch filter and is presented at the input of the FTNF (400). The FTNF can be fully integrated in CMOS IC technology (or others, e.g., Bipolar, BiCMOS, and SiGe) and applied in wireless receiver systems including EDGE/GSM, Wideband Code Division Multiple Access (WCDMA), Bluetooth, and wireless LANs (e.g., IEEE 802.11). In addition, embodiments of a generalized FTNF for wideband applications are presented.