Multi-Path LO Leakage Dodging for RF Carrier Transmission
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Solution Overview
Problem
RF transmitters face challenges in satisfying RF emission specifications due to local oscillator (LO) leakage, particularly in multi-carrier transmissions where the instantaneous bandwidth exceeds the occupied bandwidth, leading to adjacent channel leakage and out-of-band emissions.
Innovation Solution
The RF transmitter employs multiple transmit paths, each with a dedicated local phase-locked loop (PLL) for upconversion mixing, generating LO signals specific to each carrier bandwidth to minimize LO leakage and comply with emission specifications.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a single local oscillator is used for multi-carrier transmission, then device complexity is reduced, but adjacent channel leakage and out-of-band emissions increase
Solution Approach 1:
The patent divides the single local oscillator into multiple separate local oscillators, each dedicated to a specific transmit path. This segmentation allows each oscillator to generate LO signals at frequencies that fall within the occupied bandwidth of their respective carriers, preventing LO leakage into adjacent channels while maintaining manageable system complexity through modular architecture.
Solution Approach 2:
Each transmit path is equipped with its own local oscillator tailored to its specific carrier frequency and bandwidth requirements. This local quality approach ensures that the LO signal characteristics are optimized for each individual path, with the LO frequency positioned within the occupied bandwidth of the corresponding carrier, thereby eliminating adjacent channel leakage without requiring all paths to use identical oscillator configurations.
2Reliability
If multiple transmit paths with dedicated PLLs are used, then RF emission specifications are met, but device complexity increases
Solution Approach 1:
The system segments the transmit function into multiple independent transmit paths, each with its own PLL and local oscillator. This segmentation enables precise control over LO leakage in each path, ensuring compliance with RF emission standards by confining LO signals within their respective occupied bandwidths, while the modular structure allows for scalable implementation.
Solution Approach 2:
Each local oscillator is configured with specific frequency parameters positioned within the occupied bandwidth of its associated carrier. By changing the LO frequency parameter from a fixed external frequency to a carrier-specific frequency within the occupied bandwidth, the system achieves compliance with emission standards while managing complexity through parameter optimization rather than hardware proliferation.
3Ease of operation
If local oscillator frequency is positioned outside carrier bandwidth, then simple frequency planning is possible, but out-of-band emissions increase
Solution Approach 1:
Instead of positioning the LO frequency outside the carrier bandwidth as in conventional systems, this patent inverts the approach by positioning the LO frequency within the occupied bandwidth of the carrier. This inversion eliminates the need for complex filtering to suppress out-of-band emissions, as the LO leakage naturally falls within the transmitted signal band where it can be accommodated without causing adjacent channel interference.
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 approach enables multi-carrier transmissions to meet RF emission standards by reducing adjacent channel leakage and out-of-band emissions, allowing power savings and supporting advanced deployment scenarios like mMIMO.
Implementation Method 1
each transmit path of the plurality of transmit paths comprises one or more respective digital-to-analog converters (DACs); one or more respective mixers coupled to the one or more respective DACs; and a respective phase-locked loop (PLL) coupled to the one or more respective mixers
Data Source
AI summary
Certain aspects of the present disclosure provide techniques for local oscillator leakage dodging for a radio frequency (RF) transmitter. An example transmitter includes multiple transmit paths, wherein each of the transmit paths comprises a DAC; a mixer coupled to the DAC; and a PLL coupled to the mixer. The transmitter further includes a memory and a processor coupled to the memory. The processor is configured to provide, to the transmit paths, a plurality of first digital baseband signals corresponding to a plurality of RF carriers, when an instantaneous bandwidth of the plurality of RF carriers is different than an occupied bandwidth of the plurality of RF carriers; and provide, to a first transmit path of the transmit paths, one or more second digital baseband signals corresponding to one or more RF carriers, when an occupied bandwidth of the RF carrier(s) matches an instantaneous bandwidth of the RF carrier(s).