Programmable Gain Current Buffer for LTE Image Rejection
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Solution Overview
Problem
Current cellular phone receiver front-end designs face complexity in supporting multiple modes and bands, requiring highly programmable analog filters to optimize ADC dynamic range and power consumption, while stringent Image Rejection (IR) is needed for LTE with higher order modulations like 64QAM.
Innovation Solution
A multimode multiband receiver with a programmable current buffer and analog filter architecture that includes differential shunt feedback LNAs, T/4 passive mixers, and programmable current buffers to optimize SNR and IR performance, using a test tone generator for IR calibration and reducing frequency response variations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If a highly programmable analog filter is used to optimize ADC dynamic range across various modes, then power consumption is saved and ADC dynamic range is optimized, but device complexity increases
Solution Approach 1:
The receiver front-end is designed with a universal programmable analog filter structure that can be configured for different filtering requirements across multiple communication modes (GSM, WCDMA, LTE, etc.). This single multi-functional filter replaces what would otherwise require multiple mode-specific filters, reducing overall device complexity while maintaining the ability to optimize ADC dynamic range and power consumption for each mode.
Solution Approach 2:
The analog filter employs dynamic reconfiguration capability where filter coefficients, cutoff frequencies, and transfer functions can be programmably adjusted in real-time based on the active communication mode. This dynamic adaptability allows the filter to optimize performance for each mode without requiring separate static filter circuits, balancing complexity and functionality.
2Reliability
If stringent Image Rejection (IR) requirements are met for LTE with higher order modulations, then modulation performance improves, but receiver complexity increases
Solution Approach 1:
The receiver implements preliminary image rejection filtering in the analog domain before ADC conversion. By performing image rejection early in the signal chain with programmable analog filters, the system achieves stringent IR requirements for high-order modulations like 64QAM without requiring complex digital signal processing, thus limiting complexity growth.
Solution Approach 2:
A programmable analog filter acts as an intermediary between the RF front-end and ADC, providing the necessary image rejection and signal conditioning. This intermediate filtering stage enables the system to meet IR requirements for LTE with higher order modulations while keeping the overall receiver architecture manageable by handling complexity in the analog domain.
3Adaptability or versatility
If multiple LNA/mixer paths are implemented to support multiple bands, then band compatibility improves, but area penalty increases
Solution Approach 1:
Multiple LNA and mixer paths are merged into a shared common infrastructure. The patent describes a configuration where multiple LNAs feed into common mixer and buffer stages, allowing the system to support multiple bands through path selection rather than requiring completely separate processing chains. This merging reduces the total area compared to fully parallel implementations.
Solution Approach 2:
The receiver is segmented into modular LNA paths that can be independently configured for different bands, while sharing common downstream components. This segmentation allows flexible band support by activating only the necessary LNA paths for the current operating mode, reducing the effective area in use compared to having all paths fully implemented simultaneously.
Data Source
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AI summary
A receiver includes LNA (14)-mixer (12) arrangement, a current buffer (8, 10) arrangement and an analog filter (4,6) arrangement. The LNA (14)-mixer (12) arrangement receives a plurality of input signals and provides a wide-band input match for a specified frequency range of operation. The LNA (14)-mixer (12) arrangement includes a plurality of LNA structures and a plurality of mixer structures where each of the LNA structure path is coupled to a single mixer structure. The LNA (14)-mixer (12) arrangement outputs a first signal. The current buffer (8,10) arrangement receives the first signal and reduces the Image Rejection (IR) asymmetry between the high frequency portion and the low frequency portion of the first signal as well as provides a gain to the first signal. The current buffer (8, 10) arrangement outputs a second signal. The analog filter (4,6) arrangement receives the second signals and perform filtering and calibration.