Delta-Sigma Mixer Circuit for Harmonic Elimination
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Solution Overview
Problem
Harmonic mixing signals interfere with desired signals in wideband signal transmission applications, particularly in digital TV, due to non-ideal mixing units generating harmonics within the frequency band of interest, leading to inefficient solutions like additional mixing units and external SAW filters.
Innovation Solution
A mixer circuit utilizing a modulation output unit with a delta sigma modulator and digital domain code generator to produce pulse width modulation signals, which are then processed through a low pass filter to generate sine waves, effectively isolating the core frequency and moving harmonics to higher frequency bands, thus preventing harmonic mixing.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If direct down conversion is used to receive wideband signals, then the wanted signal can be obtained, but harmonic frequencies also appear in the output signal causing interference
Solution Approach 1:
The patent changes the parameter of the oscillation signal from a square wave to a sine wave generated through PWM modulation followed by low-pass filtering. This parameter change eliminates the harmonic components present in square waves while maintaining the fundamental frequency, thus resolving the harmonic interference problem while preserving signal reception efficiency
Solution Approach 2:
The patent introduces a low-pass filter as an intermediary component between the PWM modulator and the mixing unit. This intermediary filters out the high-frequency harmonic components generated during PWM modulation, allowing only the fundamental sine wave frequency to pass through to the mixing unit, thereby eliminating harmonic interference
2Object-affected harmful factors
If up conversion and down conversion are applied to avoid harmonic frequencies, then harmonic mixing is eliminated, but additional mixing units and external SAW filters are required increasing cost and complexity
Solution Approach 1:
The patent extracts only the fundamental frequency component from the oscillation signal by using PWM modulation followed by low-pass filtering. This extraction process removes all harmonic components (2Fo, 3Fo, nFo) from the signal before it reaches the mixing unit, eliminating the need for additional mixing units and SAW filters that would otherwise be required to remove these harmonics
Solution Approach 2:
The patent generates a clean sine wave oscillation signal by copying the desired frequency component from a square wave through PWM modulation and filtering. Instead of using multiple mixing stages to eliminate harmonics, the system creates a purified copy of the fundamental frequency that can be directly used in the mixing unit, simplifying the overall architecture
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 effectively eliminates harmonic mixing by retaining the core frequency signal while filtering out harmonics and noise, improving signal quality without the need for additional components like SAW filters, thereby enhancing the cost-effectiveness and efficiency of signal transmission.
Implementation Method 1
the modulated signal is a pulse width modulation signal (PWM signal)
Implementation Method 2
If the pulse width modulation signal is processed through a low pass filter, then a corresponding sine wave signal can be generated
Implementation Method 3
a mixing unit, for receiving an input signal and a modulated signal and mixing the input signal and the modulated signal to generate an output signal
Data Source
AI summary
A mixer for the elimination of harmonic mixing in signal transmission is presented. The mixer incorporates a mixing unit and a modulation output unit. The mixing unit receives an input signal and a modulated signal, and outputs an output signal after signal mixing. The modulation output unit is for the generation of modulated signals, which are usually pulse-width modulated. The modulation output unit includes a delta sigma modulator and a digital domain code generator. The delta sigma modulator outputs the modulated signal responding to the received oscillation signal and digital domain code, the digital domain code generator generates the digital domain code in order to provide digital domain sine wave code for the use of the delta sigma modulator. The oscillation signal may be a signal of constant hi-frequency, or a signal that has a frequency larger or equal to that of the input signal by an integer factor.