Two-Point DPLL Modulation With Phase Unwrap for Wideband PLLs
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Solution Overview
Problem
Existing wideband two-point modulation systems face limitations in bandwidth due to high-pass filtering effects in phase locked loops (PLLs), requiring improved synchronization and power efficiency.
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, using unwrap logic to reduce phase discontinuities and improve transmission characteristics, with a digital VCO circuit employing a CORDIC for rectangular-to-polar conversion and a digital power amplifier for efficient signal amplification.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If single-point modulation schemes are used to inject the modulating signal at the VCO input or frequency divider ratio, then the modulation bandwidth is improved, but the bandwidth is still inherently limited by the bandwidth of the PLL feedback loop
Solution Approach 1:
The patent divides the modulation signal into two separate paths: a high-pass component injected at the VCO input and a low-pass component injected at the frequency divider control. This segmentation allows each path to handle different frequency components independently, overcoming the bandwidth limitation of the PLL feedback loop while maintaining overall system functionality.
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 extended, but synchronization of the high-pass and low-pass modulation components becomes challenging
Solution Approach 1:
The patent employs a feedback mechanism where the phase detector compares the phase of the VCO output with the reference signal and generates an error signal. This error signal is filtered and used to adjust the frequency divider ratio, automatically synchronizing the low-pass modulation component with the high-pass component injected at the VCO input.
3Speed
If two-point modulation schemes are used to increase the available bandwidth, then the spectral response extends down to DC, but power consumption increases due to high-rate PLL operations
Solution Approach 1:
The patent dynamically adjusts the frequency divider ratio in response to the low-pass modulation component, allowing the PLL to operate at variable rates. This dynamic operation enables the system to maintain wideband performance when needed while reducing power consumption during periods of lower modulation requirements, optimizing the trade-off between bandwidth and power usage.
Data Source
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.