DDS Signal Generator With Zero-Crossing Tracking Filter
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Solution Overview
Problem
Conventional phase locked loop (PLL) frequency synthesizers in transceivers generate spurious frequencies due to oscillator coupling, leading to unintended signal reception or transmission, and direct digital synthesis (DDS) is costly and power-intensive due to high-speed DACs and wideband filters, making it impractical to generate multiple clock signals with high spectral purity.
Innovation Solution
A signal generator with direct digital synthesis and a narrow-band tracking filter, where the filter is tuned using a digital control unit based on zero crossings to suppress wideband noise and spurious responses, reducing the requirements on DACs and filters, and implemented with passive components for minimal power consumption.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If conventional phase locked loop (PLL) frequency synthesizers are used to generate clock signals, then multiple clock signals can be generated, but spurious frequencies are produced due to oscillator coupling causing unintended signal reception or transmission
Solution Approach 1:
The patent extracts the frequency synthesis function from traditional PLL oscillators and implements it digitally through DDS. The digital signal generator produces clock signals without physical oscillators, thereby eliminating oscillator coupling and spurious frequency generation while maintaining the ability to generate multiple clock signals with different frequencies and phases
Solution Approach 2:
The patent replaces the mechanical/physical PLL oscillator system with a digital signal generation system. Instead of using physical oscillators and mixers that generate spurious frequencies, the system uses digital signal processing with lookup tables and digital-to-analog conversion to generate clean clock signals
2Object-generated harmful factors
If direct digital synthesis (DDS) is used to generate clock signals, then spurious frequencies are suppressed, but the solution becomes expensive and power-intensive due to high-speed DACs and wideband filters
Solution Approach 1:
The patent implements a dynamic tracking filter whose center frequency automatically follows the generated clock signal frequency. This allows the use of narrow-band filters instead of wideband filters, significantly reducing power consumption and chip area while maintaining effective suppression of spurious frequencies and noise
Solution Approach 2:
The patent changes the filter bandwidth parameter dynamically - using narrow bandwidth when the signal frequency is stable and well-defined. This parameter optimization reduces the power consumption and complexity of the filter while maintaining effective spurious frequency suppression
3Productivity
If high-speed DACs and wideband filters are used in DDS, then clock signals can be generated, but chip area and power consumption increase significantly
Solution Approach 1:
The tracking filter dynamically adjusts its center frequency to follow the generated clock signal, enabling the use of compact narrow-band filters instead of large wideband filters. This dynamic adaptation maintains signal generation capability while dramatically reducing chip area
Solution Approach 2:
The patent uses lookup tables to pre-store sinusoidal data, eliminating the need for complex real-time mathematical computations. This preliminary preparation of data reduces the computational complexity and hardware requirements during signal generation
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 suppresses wideband noise and spurious responses, reducing power consumption and chip area while maintaining high spectral purity, allowing for efficient generation of multiple clock signals with reduced complexity and cost.
Implementation Method 1
a digital to analog converter (DAC) connected to an output of the digital signal generator, configured to convert the digital signal to an analog signal
Implementation Method 2
a filter coupled to an output of the DAC, configured to filter the analog signal and generate the oscillator signal
Implementation Method 3
the filter is tuned using a digital control unit based on zero crossings to suppress wideband noise and spurious responses
Implementation Method 4
a comparator coupled to an output of the filter, configured to generate a signal indicating zero crossings of the filter output signal
Data Source
AI summary
A signal generator with direct digital synthesis and tacking filter to generate an oscillator signal. A digital signal generator generates a digital signal; a digital to analog converter is connected to an output of the digital signal generator and converts the digital signal to an analog signal; a filter is coupled to an output of the DAC and filters the analog signal and generates the oscillator signal; a comparator is coupled to an output of the filter and generates a signal indicating zero crossings of the filter output signal; a digital control unit is coupled to outputs of the digital signal generator and comparator and generates a control signal to tune the filter 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 before and after zero crossings of the filter output signal.