Digital Local Oscillator Synthesis in Switching Mixer Arrays
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Existing local oscillator (LO) signal synthesizers face issues such as limited frequency agility, spurs, jitter, and PLL coupling due to analog LO signal generation methods, which introduce noise and harmonics.
Innovation Solution
A digital LO signal is generated and mixed directly with an input signal using a plurality of switching mixers, eliminating the need for analog conversion and subsequent noise-introducing components like image filters and limiters, and employing segmented dynamic element matching to reduce quantization errors.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If an integer-N PLL is used to generate the LO signal, then the LO signal frequency is stable and predictable, but the frequency agility is limited because the LO frequency must be an integer multiple of the input signal frequency
Solution Approach 1:
The mixer is divided into multiple parallel mixing elements (first mixing element, second mixing element, third mixing element, fourth mixing element), each handling a different phase version of the LO signal. This segmentation allows the system to achieve frequency agility by selectively combining outputs from different elements without requiring complex PLL reconfiguration.
Solution Approach 2:
A phase interpolator is introduced as an intermediary component between the PLL and the mixing elements. The phase interpolator takes the LO signal from the PLL and generates multiple phase versions (0°, 90°, 180°, 270°) with precise phase control, enabling frequency agility without changing the PLL configuration.
2Adaptability or versatility
If a fractional-N PLL is used to provide better frequency agility, then the LO frequency can be tuned across frequency bands, but spurs and jitter are introduced
Solution Approach 1:
The mixing function is segmented into four parallel elements, each processing a different phase version of the LO signal. This segmentation allows the system to use a simpler integer-N PLL while achieving frequency tuning capability through phase interpolation, thereby avoiding the spurs and jitter associated with fractional-N PLLs.
Solution Approach 2:
The phase interpolator serves as an intermediary that provides precise phase control to multiple mixing elements. This allows the system to achieve frequency agility through phase modulation rather than frequency modulation, eliminating the spurs and jitter that would otherwise be introduced by fractional-N PLL techniques.
3Adaptability or versatility
If adjacent PLLs are used to provide frequency coverage, then the frequency range is expanded, but the PLLs interact and frequency pull each other, introducing noise
Solution Approach 1:
Multiple mixing elements processing different phase versions of the LO signal are merged into a single mixing stage. This consolidation allows the system to achieve broad frequency coverage through phase diversity rather than using multiple adjacent PLLs, thereby eliminating PLL interaction and frequency pulling effects.
4Duration of action of moving object
If analog LO signal generation is used, then the LO signal can be generated continuously, but noise and harmonics are introduced requiring image filters and limiters
Solution Approach 1:
The system replaces traditional analog LO signal generation with a digital approach using a phase interpolator that generates LO signals in the digital domain. This substitution eliminates the noise and harmonics inherent in analog oscillators while maintaining continuous signal generation capability, removing the need for image filters and limiters.
Solution Approach 2:
The LO signal generation method is changed from analog oscillation to digital phase interpolation. By changing the fundamental parameter of how the LO signal is generated (from continuous analog waveform to digitally controlled phase samples), the system achieves continuous signal generation without the noise and harmonics of analog oscillators.
Data Source
AI summary
A switching mixer array is disclosed for the mixing of a digital LO signal with an analog input signal. Each switching mixer in the array is configured to assume either a first switching state or second switching state responsive to a respective bit of the digital LO signal.