DDS Signal Generator With Tracking Filter for Spurious Suppression
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Solution Overview
Problem
Existing signal generators in wireless communication systems face challenges in generating multiple accurate high-frequency clock signals with minimal spurious frequencies, which is costly and power-consuming due to the need for high-speed DACs, large memories, and sharp low-pass filters.
Innovation Solution
A signal generator using direct digital synthesis (DDS) combined with a narrow-band tracking filter to generate oscillator signals, where the filter is tuned to track the frequency of the generated signal, effectively suppressing wideband noise and reducing the requirements on DACs and filters, leading to lower power consumption and increased dynamic range.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional PLL frequency synthesizers are used to generate multiple clock signals, then the system can generate accurate high frequency clock signals, but coupling between oscillators causes spurious frequencies that ruin system performance
Solution Approach 1:
The patent extracts only the essential function of frequency synthesis by using a single PLL to generate one clock signal, then uses digital signal processing and filtering to derive other clock signals, eliminating the need for multiple oscillators and their associated spurious emissions
Solution Approach 2:
The patent introduces a tracking filter as an intermediary component that selectively passes the desired clock signal while rejecting spurious frequencies and noise, mediating between the PLL output and the final clock signals used in the system
2Object-generated harmful factors
If DDS is used to generate clock signals, then spurious frequencies are reduced, but high-speed DACs, digital memories, and analog filters increase chip area and power consumption
Solution Approach 1:
The patent replaces expensive high-speed DACs and large digital memories with a simpler PLL-based approach combined with selective filtering, using lower-cost components that consume less power while achieving the same spectral purity goals
Solution Approach 2:
The patent changes the operating parameters of the tracking filter dynamically, adjusting its center frequency and bandwidth to match the instantaneous frequency of the DDS output, allowing the use of lower-performance DACs while maintaining signal quality
3Measurement precision
If high-speed DACs and sharp low-pass filters are used in DDS, then spectral purity is improved, but the requirements become very demanding and increase system cost
Solution Approach 1:
The tracking filter serves as an intermediary that performs the spectral purification function, allowing the DAC to operate at lower speeds and resolutions while the filter compensates by providing sharp frequency selectivity to achieve the required spectral purity
Solution Approach 2:
The patent makes the filter characteristics dynamic by continuously adjusting the tracking filter's center frequency and bandwidth to follow the DDS output frequency, allowing the system to maintain high spectral purity across a wide frequency range without requiring excessively demanding static filter specifications
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 proposed solution significantly reduces power consumption and chip area by relaxing the DAC and filter requirements, while maintaining high spectral purity and accuracy in generating oscillator signals, thus addressing the challenges of spurious frequencies and cost in existing systems.
Implementation Method 1
the filter is tuned to track the frequency of the generated signal
Implementation Method 2
A signal generator using direct digital synthesis (DDS) combined with a narrow-band tracking filter
Implementation Method 3
The digital signals are converted to analog form in high speed digital to analog converters (DACs)
Data Source
Figure 1
Figure 2(a)~2(c)
Figure 3
AI summary
A signal generator (100) with direct digital synthesis and tacking filter to generate an oscillator signal is disclosed. The signal generator (100) comprises a digital signal generator (110) configured to generate a digital signal; a digital to analog converter (120) connected to an output of the digital signal generator (110), configured to convert the digital signal to an analog signal; a filter (130) coupled to an output of the DAC (120), configured to filter the analog signal and generate the oscillator signal; a comparator (140) coupled to an output of the filter (130), configured to generate a signal indicating zero crossings of the filter output signal; a digital control unit (150) coupled to outputs of the digital signal generator (110) and comparator (140), configured to generate a control signal to tune the filter (130) to track a center frequency of the generated oscillator signal. The control signal is generated based on adjacent samples values from the digital signal generator (110) before and after zero crossings of the filter output signal.