Frequency-Translational Bandpass Filter With Harmonic Blocker Rejection
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Solution Overview
Problem
Traditional high-Q frequency translational bandpass filters replicate the wanted pass-band around the local oscillator harmonics, leading to insufficient attenuation of unwanted blocker signals, which can saturate the receiver and degrade performance.
Innovation Solution
The implementation of transconductance cells with varying transconductance weighting to suppress frequency components corresponding to local oscillator harmonics while maintaining unattenuated wanted frequency components, using multiple transconductance cells and frequency conversion cells to convert RF voltage signals into RF current signals and mix them with non-overlapping local oscillator signals, forming a high-Q filter with enhanced harmonic rejection.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If traditional high-Q frequency translational bandpass filters are used to provide programmable filtering, then the wanted pass-band is filtered effectively, but unwanted blocker signals around LO harmonics are not significantly attenuated
Solution Approach 1:
The filter is divided into multiple frequency conversion cells, each handling a specific frequency component. Each cell processes signals at different harmonics independently, allowing selective attenuation of blocker signals at LO harmonics while maintaining the wanted pass-band.
Solution Approach 2:
Different frequency conversion cells are assigned different local oscillator signals with specific phases and frequencies tailored to their function. This allows each cell to have optimized characteristics for its specific frequency range, achieving both high-Q filtering and harmonic rejection.
2Reliability
If frequency translational bandpass filtering is applied, then receiver sensitivity to wanted signals is improved, but receiver saturation from harmonic blockers occurs
Solution Approach 1:
The filter performs preliminary attenuation of blocker signals at LO harmonics before the signals reach the baseband amplifier. By suppressing these harmful signals in advance, the receiver is protected from saturation while maintaining sensitivity to wanted signals.
3Object-affected harmful factors
If multiple frequency conversion cells with varying transconductance weighting are used to suppress harmonic blockers, then harmonic rejection is enhanced, but device complexity increases
Solution Approach 1:
Multiple frequency conversion cells are merged into a single integrated filter structure that processes multiple frequency components simultaneously. The cells share common circuit elements and are controlled by a unified architecture, reducing overall complexity compared to separate filtering stages.
Solution Approach 2:
Each frequency conversion cell is designed to handle multiple functions: frequency translation, signal filtering, and harmonic suppression. The varying transconductance weighting allows the same basic cell structure to adapt to different frequency components, reducing the need for specialized circuits for each function.
Data Source
AI summary
A high quality factor frequency translated bandpass filter (FTBPF) with harmonic rejection includes multiple transconductance cells configured to convert a received radio frequency (RF) voltage signal into respective RF current signals. Each of the transconductance cells are weighted such that the FTBPF has an effective transconductance of a first magnitude for frequency components of the received RF voltage signal arising from a first harmonic and an effective transconductance of a second magnitude less than the first magnitude for frequency components of the received RF voltage signal arising from harmonics at integer multiples of the first harmonic. The FTBPF also includes multiple frequency conversion cells coupled to the transconductance cells and configured to mix respective ones of the RF current signals with multiple non-overlapping local oscillator signals. The FTBPF also includes multiple baseband impedances coupled to outputs of the frequency conversion cells and ground and are frequency translated by mixed signals from the frequency conversion cells.