Multimode RF Receiver Complex Filter Design
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Solution Overview
Problem
RF receivers face challenges in rejecting unwanted signals and addressing sideband asymmetry in gains, particularly in multi-standard wireless communication systems like 2G and 3G, where frequency response symmetry is compromised.
Innovation Solution
The RF receiver design incorporates a first and second mixer with an impedance circuit to decouple channels and a digital filter with complex coefficients to compensate for frequency response asymmetry, allowing operation across multiple standards without disabling mixers or clocks, and utilizing polyphase reactive circuits to enhance filter quality.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If quadrature down conversion is used to down convert RF signals, then the received RF signal can be converted to baseband signal, but image signals are produced that require additional filtering
Solution Approach 1:
The patent applies quadrature down conversion which inherently produces image signals, but then uses the I and Q channels with complex filtering to convert this harmful effect into a benefit by selectively filtering and combining the channels to recover the desired signal while rejecting images and interferers
2Object-affected harmful factors
If bandpass filtering is used to remove interfering signals, then desired signals can be passed and interfering signals removed, but the quality factor limits the effectiveness at removing nearby frequency signals
Solution Approach 1:
The patent segments the filtering function across multiple components: RF filtering stage, IF filtering stage, and digital signal processing stage. This segmentation allows each stage to handle specific frequency ranges and types of interference, achieving better overall selectivity than a single bandpass filter could provide
Solution Approach 2:
The patent transitions from analog frequency-domain filtering to digital time-domain processing by converting IF signals to digital samples and applying digital filtering algorithms. This dimensionality change enables more precise control over frequency response and better rejection of nearby interferers
3Adaptability or versatility
If the receiver supports multiple communication standards (2G and 3G), then versatility is improved, but frequency response asymmetry and gain differences occur between standards
Solution Approach 1:
The patent implements dynamic configuration of the receiver chain, allowing different mixing schemes (direct conversion for 2G, super-heterodyne for 3G), different filtering parameters, and different signal processing paths to be activated depending on the detected communication standard, thereby maintaining optimal performance across standards
Solution Approach 2:
The patent changes key operating parameters including local oscillator frequency, mixing architecture, and digital filter coefficients based on the communication standard being received, allowing the same hardware to optimize its frequency response and gain characteristics for each standard
4Object-affected harmful factors
If SAW filters are used for RF filtering, then signal selectivity is improved, but device complexity and cost increase
Solution Approach 1:
The patent extracts the filtering function from dedicated hardware components (SAW filters) and distributes it across multiple stages including simple analog filters and digital signal processing algorithms, eliminating the need for complex RF filtering hardware while maintaining selectivity performance
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 configuration improves frequency response symmetry and supports multiple communication modes, enhancing receiver selectivity and reducing the need for SAW filters, while compensating for asymmetrical frequency responses to ensure consistent signal amplification across the desired bandwidth.
Implementation Method 1
A mixer mixes RF input signals with LO signals and translates the impedance of the polyphase reactive circuit into the RF input impedance of the mixer
Implementation Method 2
When fed from a high impedance source, such as a current source, the mixer provides a high quality factor (Q) impedance response associated with an impedance peak
Implementation Method 3
received RF signals are mixed using mixers with a local oscillator (LO) signal to down convert the received RF signals into lower frequency signals
Implementation Method 4
down convert the received RF signals into lower frequency signals, which are, known as intermediate frequency (IF) signals
Implementation Method 5
a digital filter with complex coefficients to compensate for frequency response asymmetry
Data Source
AI summary
One aspect of the present invention includes a radio frequency (RF) receiver having a first mixer and a second mixer. The first mixer may be an I-mixer and the second mixer a Q-mixer for downconverting the received RF signal. An impedance circuit is disposed between the first mixer and the second mixer to decouple the channels. In another aspect of present invention, the RF receiver includes a digital filter having at least one complex coefficient. The digital filter exhibits asymmetrical frequency response, and may be used to compensate the asymmetrical frequency response of another filter in the RF receiver.