Two-Point DPLL Modulation for Wideband Phase Synchronization
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Solution Overview
Problem
Existing two-point modulation systems face limitations in bandwidth due to high-pass characteristics of phase-locked loops, synchronization challenges, and high power consumption, particularly in PLL operations.
Innovation Solution
A two-point modulation apparatus and method that injects both a wrapped-phase and a differentiated unwrapped-phase signal into a phase-locked loop, utilizing CORDIC circuits for rectangular-to-polar conversion and digital switching amplifiers to control tank capacitances, thereby improving transmission characteristics and maintaining compliance with mask requirements.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If single-point modulation schemes are used to inject the modulating signal at the VCO input or frequency divider ratio, then the PLL configuration can be maintained, but the bandwidth of the modulation is inherently limited by the bandwidth of the PLL feedback loop
Solution Approach 1:
The modulation signal is segmented into two separate injection points: one at the VCO input and another at the frequency divider ratio control. This segmentation allows different frequency components to be injected at optimal locations, with the VCO input handling low-frequency components and the frequency divider handling high-frequency components, thereby overcoming the bandwidth limitation of single-point modulation while maintaining PLL stability.
2Speed
If two-point modulation schemes are used to inject the modulating signal at both the VCO and frequency divider controllers, then the bandwidth is increased, but synchronization of the high-pass and low-pass modulation components becomes challenging
Solution Approach 1:
A feedback mechanism is implemented to monitor and adjust the phase and frequency of the two modulation components. The system measures the actual output frequency and phase, compares them with the desired values, and uses this error information to adjust the modulation signals at both injection points, ensuring they remain synchronized despite variations in operating conditions.
3Reliability
If two-point modulation schemes are used to compensate for high-pass characteristics, then the spectral response extends down to DC, but high power consumption results from high-rate PLL operations
Solution Approach 1:
Instead of using full two-point modulation at all times, the system employs partial modulation by dynamically adjusting the modulation depth and frequency at each injection point based on the required output spectrum. When full bandwidth is not needed, the system reduces the modulation intensity, thereby maintaining spectral response quality when needed while reducing power consumption during normal operation.
Data Source
Figure 1
Figure 2A~2B
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AI summary
A digitally controlled oscillator (DCO) modulation apparatus and method provides a wideband phase-modulated signal output. An exemplary modulator circuit uses an oscillator in a phase-locked loop. The circuit receives a wrapped-phase input signal, unwraps the wrapped-phase input signal to generate an unwrapped-phase signal, and differentiates the unwrapped-phase signal. The wrapped-phase input signal and the differentiated unwrapped-phase signal are both injected into a feedback loop of the modulator circuit. The feedback loop may include a multi-modulus frequency divider with a frequency divisor that is temporarily incremented or decremented to cancel out abrupt phase jumps associated with the wrapped-phase to unwrapped-phase conversion.