RF Front-End Filter Delay Matching with Tunable Analog Path
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Solution Overview
Problem
Conventional RF front end filters in base stations face challenges with size, reconfigurability, and high insertion loss due to group delay mismatch between RF and DSP paths, limiting their ability to meet diverse frequency specifications and standards.
Innovation Solution
A system with two parallel feed forward paths, one containing a digital filter and the other a tunable analog filter, where the tunable analog filter reduces the delay mismatch by offsetting impulse responses, allowing for a shorter delay line and improved reconfigurability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If a digital filter is used in the RF front end, then reconfigurability and frequency agility are improved, but group delay mismatch with the RF path increases
Solution Approach 1:
The feed forward path is segmented into two parallel paths: a digital signal processing path and an RF path. Each path is independently optimized, with the digital path containing ADC, digital filter, and DAC, and the RF path containing analog filters and amplifiers. This segmentation allows independent tuning of each path's group delay characteristics.
Solution Approach 2:
A tunable analog filter is introduced as an intermediary component in the digital signal processing path to compensate for group delay mismatch. This analog filter acts as a mediator that adjusts the group delay of the digital path to match the RF path, enabling both reconfigurability and precise delay matching.
2Manufacturing precision
If the delay line is lengthened to compensate for group delay mismatch, then group delay matching is improved, but physical space and cost increase
Solution Approach 1:
Instead of physically lengthening the delay line, the invention changes the electrical parameters of the tunable analog filter (cut-off frequency, Q-factor, center frequency) to adjust group delay characteristics. This parameter-based adjustment achieves group delay matching without increasing physical dimensions.
3Reliability
If high-order filtering is implemented, then filtering performance is improved, but device complexity and physical size increase
Solution Approach 1:
The invention replaces complex high-order analog filters with a combination of lower-order analog filters and digital signal processing. The digital filter (FIR or IIR) performs the high-order filtering function in the digital domain, eliminating the need for complex analog filter structures with multiple resonators and reducing overall device complexity.
4Adaptability or versatility
If switches are used to connect high Q components for reconfigurability, then frequency agility is improved, but insertion loss increases
Solution Approach 1:
A coupler is introduced as an intermediary device to combine the outputs of the digital signal processing path and RF path. The coupler provides isolation between the two paths, allowing independent optimization of each path's components without mutual interference, thereby minimizing insertion loss while maintaining frequency agility.
Data Source
AI summary
A radio frequency (RF) front end having group delay mismatch reduction is provided. One embodiment provides a first feed forward path and a second feed forward path. The second feed forward path is electrically in parallel with the first feed forward. The second feed forward path has a first signal path and a second signal path. The first and second signal paths are arranged to be electrically in parallel. The first signal path has a digital filter. The second signal path has a tunable analog filter. The tunable analog filter operates to reduce a delay associated with the second feed forward path as compared with a delay associated with the first feed forward path.