Digital Frequency Synthesizer Residue Cancellation for Fine Resolution
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Solution Overview
Problem
Conventional analog frequency synthesizers face challenges in reducing size, cost, and increasing reliability due to the complexity of integrating RF circuitry in wireless devices, particularly in achieving fine frequency resolution and minimizing phase errors.
Innovation Solution
The implementation of digital frequency synthesizers (DFSs) that utilize a time-to-digital converter (TDC) to measure phase differences and a sigma-delta modulator (SDM) with adaptive gain scaling to cancel residue signals, along with a digital loop filter to control a digitally controlled oscillator (DCO), reducing the reliance on analog components and enhancing precision.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Area of moving object
If analog frequency synthesizers are used, then frequency generation capability is achieved, but area usage increases and manufacturing precision decreases
Solution Approach 1:
The patent replaces analog frequency synthesizer circuitry with a digital frequency synthesizer architecture. The TDC converts phase differences to digital values, the SDM processes these digitally, and the DCO generates frequencies based on digital control words. This substitution of digital for analog systems reduces area usage and improves immunity to fabrication variations while maintaining frequency generation capability.
Solution Approach 2:
The patent changes the operational parameters from analog continuous signals to digital discrete values. The TDC measures phase difference and converts it to a digital value, which is then processed by the SDM to generate a digital control word for the DCO. This parameter transformation from analog to digital domain enables reduced area and improved manufacturing precision.
2Measurement precision
If conventional frequency synthesizer architectures are used, then frequency generation is achieved, but frequency resolution and phase error performance deteriorate
Solution Approach 1:
The patent segments the frequency synthesizer into distinct functional blocks: TDC for phase-to-digital conversion, SDM for spectral shaping and residue cancellation, and DCO for frequency generation. This segmentation allows each block to be optimized independently, achieving fine frequency resolution through the TDC's phase measurement capability while managing complexity through modular digital implementation.
Solution Approach 2:
The patent introduces a digital intermediary processing path between phase measurement and frequency generation. The TDC output is processed by the SDM, which acts as an intermediary to shape the spectrum and cancel residues before the final DCO generation. This digital intermediary enables fine frequency resolution without proportionally increasing analog circuit complexity.
3Reliability
If digital frequency synthesizers with residue cancellation are implemented, then phase error is reduced, but circuit complexity increases
Solution Approach 1:
The patent implements a feedback mechanism where the TDC continuously measures the phase difference between the reference signal and the DCO output, converting it to a digital value. The SDM processes this feedback to generate control words that adjust the DCO frequency, thereby reducing phase errors through closed-loop digital control.
Solution Approach 2:
The patent replaces complex analog phase error correction circuits with a digital implementation. The TDC, SDM, and digital control logic substitute for traditional analog phase detectors, charge pumps, and loop filters, achieving phase error reduction through digital processing while reducing overall circuit complexity.
Data Source
AI summary
An apparatus includes a digital frequency synthesizer (DFS). The DFS includes a time-to-digital converter (TDC) to provide an output signal that represents a phase difference between a reference signal and a feedback signal. The DFS further includes a scaling circuit, which has an adaptively changed gain, to provide a scaled residue signal used to cancel an effect of the residue signal in the DFS.