Nested Delta-Sigma Modulator for Precise Wide-Range RF Synthesis
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Radio frequency synthesizers face challenges in generating precise frequencies over a large range due to the trade-off between resolution and range, with existing fractional-N synthesizers often resulting in frequency errors and undesirable spurs when using a power-of-two modulus.
Innovation Solution
A nested fractional-N frequency synthesizer system is introduced, utilizing two distinct Digital Delta-Sigma Modulators (DDSMs) with programmable moduli M1 and M2 to set the output frequency exactly, improving spectral performance and reducing spurs by allowing the frequency step to be set exactly while maintaining the advantages of a power-of-two modulus divider.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a power-of-two modulus is used in fractional-N synthesizer, then the device complexity is reduced and transient response is faster, but frequency precision deteriorates and spurs are generated
Solution Approach 1:
The modulus M is segmented into two separate moduli: M1 (power of two) and M2 (programmable). The frequency synthesis is divided into two stages with two DDSMs, where the first DDSM uses M1 for fast transient response and the second DDSM uses M2 for precise frequency control. This segmentation allows each modulus to specialize in one function, resolving the contradiction between speed and precision.
Solution Approach 2:
The patent implements a nested structure where the second DDSM (with modulus M2) is embedded within the overall frequency synthesis system that already contains the first DDSM (with modulus M1). The output of the second DDSM feeds into the first DDSM, creating a nested configuration. This nested architecture enables the system to maintain the simplicity of power-of-two division while incorporating programmable precision through the inner nested module.
2Speed
If a power-of-two modulus is used in fractional-N synthesizer, then the transient response is faster, but frequency precision deteriorates
Solution Approach 1:
The transient response function is assigned to the first DDSM with power-of-two modulus M1, while the frequency precision function is assigned to the second DDSM with programmable modulus M2. The first DDSM's power-of-two structure enables fast switching and rapid transient response, while the second DDSM's programmable structure enables precise frequency setting, thus resolving the speed-precision contradiction through functional segmentation.
Solution Approach 2:
The system dynamically switches between the characteristics of power-of-two division and programmable division by using two parallel DDSMs. The first DDSM provides dynamic fast response characteristics, while the second DDSM provides static precision characteristics. The combination allows the system to exhibit both fast transient response and high frequency precision simultaneously.
3Measurement precision
If frequency resolution is increased in synthesizer, then the frequency generation precision is improved, but the radio frequency range is reduced
Solution Approach 1:
The frequency synthesis range is segmented into two domains: the first DDSM with modulus M1 covers a wide frequency range with lower resolution, while the second DDSM with programmable modulus M2 provides fine frequency resolution within a specific range. The mathematical relationship fVCO = (N0 + N1/M1 + N2/M2) × fPD combines both wide range and high resolution, resolving the contradiction between range and precision.
Solution Approach 2:
The patent adds an additional dimension to the frequency synthesis by introducing a second fractional term N2/M2 alongside the existing N1/M1 term. This creates a two-dimensional frequency control space where M1 handles the coarse frequency range selection and M2 handles the fine frequency resolution adjustment, effectively expanding the system's capability to provide both wide range and high precision simultaneously.
Data Source
AI summary
Methods and systems are disclosed that provide a radio frequency synthesizer that generates precise frequencies over a large radio frequency range. The radio frequency synthesizer can provide a high resolution of frequency generation and still provide precise frequencies over a range of radio frequencies. The precision and resolution while maintaining a large operating range come from the ability of the frequency synthesizer to generate frequencies as a product of a plurality of moduli. For example, the frequency can be generated from a reference frequency using a first modulus and a second modulus. The plurality of modulo can be implemented using nested digital delta-sigma modulators in a fractional-N frequency synthesizer.