Quadrature Multi-Mode RF Receiver with Dynamic VLIF Frequency
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Solution Overview
Problem
RF receivers in UMTS systems face challenges in supporting both WBCDMA and EGPRS protocols with different architectures, requiring efficient operation in multiple modes while minimizing power consumption, cost, and complexity, and effectively rejecting image frequencies with varying signal strengths.
Innovation Solution
A quadrature multi-mode RF receiver using a single quadrature mixer that adjusts the VLIF frequency based on signal strength, employing programmable filters and gain/phase correction circuitry to improve image rejection, and converting signals to digital for enhanced filtering.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a single receive path is used for both WBCDMA and EGPRS protocols, then cost, complexity, and current consumption are reduced, but the receiver cannot efficiently support both protocols with different architectural requirements
Solution Approach 1:
The receiver employs a single quadrature mixer that can dynamically switch between two operating modes: direct conversion mode for WBCDMA protocol and VLIF mode for EGPRS protocol. The local oscillator frequency is adjustable to enable the mixer to function at different frequencies, allowing the same hardware to adapt to different protocol requirements without requiring separate receive paths
Solution Approach 2:
The single quadrature mixer is designed to perform multiple functions by supporting both direct conversion and VLIF operating modes. This universal mixer replaces what would traditionally require two separate mixers (one for each protocol), thereby reducing device complexity while maintaining the ability to support both WBCDMA and EGPRS protocols
2Object-affected harmful factors
If a lower VLIF frequency is used, then image rejection is improved, but 1/f noise, DC offsets, and IIP2 problems increase, reducing receiver sensitivity
Solution Approach 1:
The receiver dynamically adjusts the VLIF frequency based on the strength of the desired signal. When the desired signal is strong, the receiver operates at a lower VLIF frequency to maximize image rejection. When the desired signal is weak, the receiver switches to a higher VLIF frequency to minimize 1/f noise and DC offset effects, thereby maintaining optimal receiver sensitivity across varying signal conditions
Solution Approach 2:
The system changes the operating frequency parameter of the quadrature mixer based on signal strength conditions. By varying the local oscillator frequency, the receiver can shift between different VLIF frequencies to optimize performance for different signal scenarios, balancing image rejection and sensitivity requirements
3Reliability
If a higher VLIF frequency is used, then receiver sensitivity is improved, but image rejection deteriorates
Solution Approach 1:
The receiver employs dynamic frequency adjustment where the VLIF frequency is selected based on the strength of the desired signal. For weak signals, a higher VLIF frequency is used to maximize sensitivity and minimize noise. For strong signals, a lower VLIF frequency is used to maximize image rejection, creating an adaptive system that optimizes performance based on real-time signal conditions
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
The solution enables efficient operation in both direct conversion and VLIF modes, reducing noise and inter-modulation effects, and effectively rejecting image signals, while maintaining low cost and complexity, thus improving receiver sensitivity and image rejection based on signal strength.
Implementation Method 1
a received RF signal is mixed with a local oscillator signal to obtain a lower intermediate frequency (IF) signal
Implementation Method 2
A quadrature receiver architecture uses two mixers receiving the same RF input signal, which is mixed with two different local oscillator signals that are equal in frequency and phase-shifted from each other by 90 degrees
Data Source
AI summary
The present invention is a quadrature multi-mode RF receiver that uses a single quadrature mixer for tuning to desired frequency bands. In a direct conversion mode of operation, the RF receiver down converts a received RF signal directly into a baseband signal. In a VLIF mode of operation, the RF receiver down converts a received RF signal into a VLIF signal. When receiving a wanted RF signal, the frequency of the resulting VLIF signal is called the wanted VLIF frequency, and is based on the signal strength of the received RF signal. In one embodiment of the present invention, the wanted VLIF frequency is selected to be one of two VLIF frequencies. The wanted VLIF frequency is inversely related to the signal strength of the received RF signal.