Overlapping LO Pulse Mixer for Lower Counter Intermodulation
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Solution Overview
Problem
Existing wireless transmitters face challenges in reducing counter intermodulation (CIM) performance, particularly CIM3 and CIM5, due to the harmonics generated by square waves from local oscillators, which can lead to waveform distortion and emission constraints violations.
Innovation Solution
The implementation of an electronic circuit that uses overlapping local oscillator (LO) clock signals with specific duty ratios greater than 100/N % and phase differences of 360/N °, where N is the total number of pulse signals, to effectively mix with phase-shifted input signals, thereby reducing CIM without increasing the number of phases.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If square waves from local oscillators are used for mixing, then the mixing function is achieved, but harmonics are generated causing CIM distortion
Solution Approach 1:
The local oscillator signal is segmented into multiple phase-shifted pulse signals (N phases) instead of using a single square wave. Each phase contributes to the mixing process, and their combined effect cancels harmful harmonics while maintaining the mixing function.
Solution Approach 2:
The pulse signals use asymmetric duty ratios (greater than 100/N %) that differ from the conventional 50% or equal-phase distribution. This asymmetric duty ratio design creates overlapping time windows that enable harmful harmonic cancellation while preserving signal mixing capability.
2Reliability
If multiple pulse signals with specific duty ratios are used, then CIM performance is improved, but circuit complexity increases
Solution Approach 1:
The system uses periodic pulse signals with specific duty ratios and phase shifts. By configuring N pulse signals with duty ratios greater than 100/N % and appropriate phase differences, the system achieves periodic overlapping that cancels CIM harmonics without requiring complex additional circuitry.
Solution Approach 2:
The invention changes key parameters of the local oscillator signals: duty ratio (greater than 100/N %) and phase difference (360/N degrees). These parameter modifications enable CIM reduction through harmonic cancellation while using the same basic mixer architecture, thus avoiding increased circuit complexity.
3Object-generated harmful factors
If overlapping pulse signals are used to cancel harmonics, then CIM distortion is reduced, but signal overlap causes interference
Solution Approach 1:
The invention converts the potentially harmful effect of signal overlap into a beneficial harmonic cancellation mechanism. By carefully designing the duty ratio (greater than 100/N %) and phase relationships, the overlapping regions create destructive interference for harmful harmonics while preserving the desired signal components through constructive 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 significantly reduces CIM3 and CIM5 by canceling or minimizing the frequency components that cause these intermodulation distortions, improving transmission performance without increasing circuit complexity or power consumption.
Implementation Method 1
a mixer circuit configured to mix the plurality of differential signal pairs with a plurality of pulse signals to obtain a pair of differential mixer output signals
Data Source
AI summary
An electronic circuit is provided. The electronic circuit includes an input port configured to receive an in-phase (I) data signal and a quadrature (Q) data signal. The electronic circuit includes a conversion circuit configured to convert the I data signal and the Q data signal to a plurality of differential signal pairs. The electronic circuit includes a mixer circuit configured to mix the plurality of differential signal pairs with a plurality of pulse signals to obtain a pair of differential mixer output signals. The electronic circuit includes a variable gain amplifier (VGA) configured to generate an output signal based on the pair of differential mixer output signals. The plurality of pulse signals have a same duty ratio that is greater than 100/N %, where N is a total number of the plurality of pulse signals. A phase difference between two consecutive pulse signals equals 360/N °. Also provided is a method.