研究目的
To design and implement a sigma-delta fractional-N frequency synthesizer with two-point modulation for FMCW radar applications, aiming to achieve wide bandwidth, low phase noise, high linearity, and programmable chirp parameters.
研究成果
The implemented synthesizer successfully achieves a continuous tuning range over 800 MHz, low phase noise (-93.32 dBc/Hz at 1 MHz offset), and programmable chirp parameters with RMS frequency errors as low as 112 kHz. The two-point modulation technique proves effective in decoupling loop bandwidth from chirp slope, enabling high linearity and fast chirp capabilities. This work demonstrates the potential for mm-wave FMCW synthesizers in radar applications, with suggestions for future improvements in calibration techniques and bandwidth extension.
研究不足
The maximum measurable chirp bandwidth is limited to 640 MHz due to the 160 MHz real-time analysis bandwidth of the Keysight N9030A spectrum analyzer, despite the designed bandwidth of up to 800 MHz. Gain mismatch in the high-pass modulation path requires pre-distortion calibration, and the D/VCO design complexity may increase area and power consumption.
1：Experimental Design and Method Selection:
The study employs a fractional-N phase-locked loop (PLL) architecture with two-point modulation (TPM) to decouple loop bandwidth from chirp slope. Key components include a digital and voltage controlled oscillator (D/VCO), divider chain, phase and frequency detector (PFD), charge pump (CP), loop filter, sigma-delta modulator, and modulation signal generator. Theoretical models for TPM are used to ensure gain and delay matching between modulation paths.
2：Sample Selection and Data Sources:
The synthesizer is implemented as a monolithic chip using TSMC 65 nm CMOS process. Measurements are conducted on a bonded chip on a printed circuit board (PCB) with RF outputs connected via SMAs.
3：List of Experimental Equipment and Materials:
Equipment includes Keysight real-time spectrum analyzer N9030A and Keysight 89600 vector signal analysis (VSA) software for frequency error measurement. Materials involve the CMOS chip, PCB, and bonding components.
4：Experimental Procedures and Operational Workflow:
The synthesizer is tested in PLL locking mode and FMCW mode (open loop, one-point modulation, and two-point modulation). Control words are set via an integrated SPI interface, and frequency, phase noise, and error are measured using spectrum analyzers and VSA software.
5：Data Analysis Methods:
Data analysis includes calculating phase noise, RMS frequency error, and comparing performance across different modes. Statistical methods are implied for error calculation, using manufacturer software tools.
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