Baseband Harmonic Rejection Circuit for 4G Transmitters
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Solution Overview
Problem
Current transmitters for 4G wireless communication, particularly those using LTE standards, face performance degradation due to counter-intermodulation products (C-IM3) generated by baseband non-linearity and LO harmonics, which affect frequency division duplexing and spectral emission requirements, and existing solutions either increase design complexity, power consumption, or fail to adequately address baseband-generated C-IM3 components.
Innovation Solution
A circuit with two baseband sections generating phase-shifted baseband signals, which are then mixed with phase-rotated local oscillator signals and scaled, allowing for the combination of upconverted signals to reduce C-IM3 products, leveraging harmonic rejection techniques to suppress third-order baseband harmonics while minimizing area and power consumption increases.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If baseband non-linearity compensation is increased to reduce C-IM3 products, then transmitter performance improves, but design complexity and power consumption increase
Solution Approach 1:
The baseband signal is divided into three separate signal paths, each processing a different phase-rotated version of the baseband signal. This segmentation allows independent optimization of each path while collectively achieving C-IM3 reduction, resolving the contradiction by distributing complexity across multiple simpler parallel paths rather than one complex sequential path.
Solution Approach 2:
Phase-rotated local oscillator signals are introduced as intermediaries to rotate the phase of baseband signals before mixing. These phase-rotated LO signals act as mediators that enable the cancellation of C-IM3 products through constructive and destructive interference, improving transmitter performance without requiring complex baseband non-linearity compensation circuits.
2Reliability
If baseband non-linearity compensation is increased to reduce C-IM3 products, then transmitter performance improves, but power consumption increases
Solution Approach 1:
The signal is split into three paths with different phase rotations, allowing the use of simpler, lower-power baseband processing in each path. The collective effect of these three simpler paths achieves C-IM3 reduction more efficiently than a single complex baseband compensation circuit, thereby reducing overall power consumption while maintaining transmitter performance.
Solution Approach 2:
The invention changes the phase parameter of the local oscillator signals (0°, 120°, 240° rotations) to create phase-diversity in the three signal paths. This parameter change enables natural cancellation of C-IM3 products through phase interference, replacing the need for power-intensive active non-linearity compensation and reducing overall power consumption.
3Device complexity
If traditional single path mixing is used, then device complexity is low, but C-IM3 products cannot be adequately reduced
Solution Approach 1:
The single mixing path is segmented into three parallel paths, each with a different phase rotation (0°, 120°, 240°). This segmentation increases device complexity only slightly while enabling effective C-IM3 reduction through the combined output of the three paths, where harmful intermodulation products cancel each other out.
Solution Approach 2:
Three separately mixed and phase-rotated signals are merged/combined at the output to produce the final transmitted signal. This combining process is where the magic happens: the desired signal components add constructively while the C-IM3 products cancel through destructive interference, achieving harmful factor reduction with minimal complexity increase.
4Object-generated harmful factors
If phase-rotated LO signals are used for harmonic rejection, then C-IM3 products are reduced, but area consumption increases
Solution Approach 1:
The same baseband sections and mixing circuits are used across all three signal paths, with only the LO phase connections differing. This multi-functional reuse of components achieves C-IM3 reduction without proportionally increasing circuit area, as each component serves multiple purposes across the three phase-rotated paths.
Solution Approach 2:
Instead of adding complex filtering or cancellation circuits that would consume significant area, the invention changes only the phase parameter of the LO signals connecting to the baseband sections. This parameter change approach achieves harmonic rejection and C-IM3 reduction with minimal additional area, as it leverages existing circuitry with different phase connections.
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 effectively reduces C-IM3 products, improving transmitter performance by canceling intermodulation distortions and meeting spectral emission requirements without excessive power consumption or area expansion, thus enhancing the efficiency and reliability of 4G wireless communication.
Implementation Method 1
a mixer for multiplication of the baseband signal with a local oscillator signal, so that an upconverted signal is obtained
Implementation Method 2
The local oscillator signal in one signal path is a phase-rotated version of the local oscillator signal in the other two signal paths, so that three upconverted signals with rotated phase with respect to each other are obtained
Implementation Method 3
three upconverted signals with rotated phase with respect to each other are obtained. Each signal path also includes a scaling unit configured to apply a scaling factor dependent on the rotated phases
Data Source
AI summary
A circuit for reducing counter-intermodulation in a modulated signal caused by an oscillator frequency and harmonics of a baseband signal is disclosed. The circuit comprises a first and a second baseband section arranged for generating a first and a second version of a baseband signal, the second version being phase shifted with respect to the first version. The circuit further comprises three signal paths comprising mixers for multiplication of the first and second version of the baseband signal with a local oscillator signal, so that three upconverted signals with rotated phase with respect to each other are obtained, and arranged for applying a scaling with a scaling factor corresponding to the rotated phases. The circuit further comprises a combination unit arranged for combining the three upconverted signals.