Two-Point DPLL Modulation for Wideband Stability Control
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Solution Overview
Problem
Conventional digital phase-locked loops (DPLLs) face challenges in modulating oscillators with wideband signals without disturbing their normal operation, especially when the bandwidth of the modulating signal exceeds the closed-loop bandwidth of the DPLL.
Innovation Solution
A DPLL design incorporating two-point modulation, which includes a phase-to-digital converter, a loop filter, a first processing unit for lowpass modulation, and a second processing unit for highpass modulation, allowing the application of input modulating signals to separate paths within the loop to effectively increase bandwidth and support wideband modulation while maintaining minimal disturbance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If a single modulation path is used in a conventional DPLL, then the device complexity is low, but the bandwidth is limited to the closed-loop bandwidth and cannot support wideband modulation
Solution Approach 1:
The modulation function is segmented into two separate paths: a lowpass modulation path for narrowband signals and a highpass modulation path for wideband signals. Each path is optimized for its specific bandwidth range, allowing the DPLL to handle both narrowband and wideband modulation without compromising performance or stability.
2Adaptability or versatility
If the modulating signal bandwidth is wider than the closed-loop bandwidth, then wideband modulation capability is achieved, but the normal operation of the DPLL is disturbed
Solution Approach 1:
By separating modulation into lowpass and highpass paths, wideband modulation signals are routed through the highpass path that does not pass through the loop filter, preventing disturbance to the DPLL's normal operation and maintaining stability while achieving wideband modulation capability.
Solution Approach 2:
The highpass modulation path acts as an intermediary that allows wideband modulation signals to reach the oscillator without passing through the loop filter, thereby mediating between the modulation signal and the DPLL core to prevent stability disturbance.
3Ease of operation
If modulation is applied prior to the loop filter, then narrowband modulation is supported, but wideband modulation cannot be performed without disturbing DPLL operation
Solution Approach 1:
The system segments modulation into two paths: the lowpass path applies modulation prior to the loop filter for narrowband signals, while the highpass path applies modulation after the loop filter for wideband signals, allowing both narrowband and wideband modulation capabilities to coexist without interference.
Data Source
AI summary
A digital phase-locked loop (DPLL) supporting two-point modulation is described. In one design, the DPLL includes a phase-to-digital converter and a loop filter operating in a loop, a first processing unit for a lowpass modulation path, and a second processing unit for a highpass modulation path. The first processing unit receives an input modulating signal and provides a first modulating signal to a first point inside the loop after the phase-to-digital converter and prior to the loop filter. The second processing unit receives the input modulating signal and provides a second modulating signal to a second point inside the loop after the loop filter. The first processing unit may include an accumulator that accumulates the input modulating signal to convert frequency to phase. The second processing unit may include a scaling unit that scales the input modulating signal with a variable gain.