PLL High-Pass Modulation with Digital Pre-Compensation
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Solution Overview
Problem
Existing radio frequency modulators based on direct phase or frequency modulation using phase locked loops face limitations such as narrow bandwidth, complexity in signal processing, and high power consumption, which restrict their ability to perform modulation over the entire frequency range and require complex pre-compensation filters.
Innovation Solution
A direct modulator that digitally processes the modulation signal before injection into a high-pass path of a phase locked loop, compensating for non-flat frequency responses and non-linearity of the controlled oscillator, allowing for accurate pre-compensation and adaptive filtering to achieve a flat transfer function.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If a direct modulator uses a high-pass path of a phase locked loop for modulation, then the bandwidth is improved and the ability to perform modulation over the entire frequency range is enhanced, but the frequency response becomes non-flat and requires complex pre-compensation filters
Solution Approach 1:
The patent applies preliminary action by digitally processing the modulation signal before injection into the high-pass path. A digital pre-compensation filter pre-adjusts the signal to counteract the non-flat frequency response of the high-pass PLL path, eliminating the need for complex analog pre-compensation filters and reducing device complexity while maintaining improved bandwidth
Solution Approach 2:
The patent substitutes mechanical/analog signal processing with digital signal processing. Instead of using complex analog pre-compensation filters with multiple components, the invention uses digital filtering and processing in the digital domain, replacing the mechanical system with an electronic/digital system that achieves the same pre-compensation function with reduced complexity
2Manufacturing precision
If a direct modulator uses analog pre-compensation filters to compensate for non-flat frequency response, then the frequency response flatness is improved, but component value uncertainties and manufacturing costs increase
Solution Approach 1:
The patent replaces analog pre-compensation filters with digital signal processing. Digital filters use software-based filtering algorithms instead of physical analog components, eliminating component value uncertainties and reducing manufacturing costs while maintaining frequency response flatness through programmable filter coefficients
Solution Approach 2:
The patent changes the state of the pre-compensation filter from analog (fixed physical components) to digital (programmable parameters). By using digital signal processing with adjustable filter coefficients, the system achieves precise frequency response control without the manufacturing tolerances and cost issues associated with analog component values
3Stability of the object's composition
If a direct modulator uses a controlled oscillator with narrow bandwidth loop filter, then the stability is improved, but the bandwidth is limited and cannot perform modulation over the entire frequency range
Solution Approach 1:
The patent segments the modulation signal processing into two paths: a high-pass path for high-frequency modulation components and a low-pass path for low-frequency components. This segmentation allows the narrow bandwidth loop filter to maintain stability while the digital pre-compensation and selective signal injection enable extended overall bandwidth coverage
Solution Approach 2:
The patent introduces digital pre-compensation filtering as an intermediary between the modulation signal source and the PLL input. This digital intermediary pre-processes the signal to prepare it for injection into the high-pass path, enabling the narrow bandwidth loop filter to operate stably while the system as a whole achieves extended bandwidth through the mediating digital processing stage
4Manufacturing precision
If a direct modulator uses complex signal processing to compensate for non-linearity of the controlled oscillator, then the linearity is improved, but the device complexity and power consumption increase
Solution Approach 1:
The patent replaces complex analog linearization circuits with digital signal processing. By using digital algorithms to compensate for controlled oscillator non-linearity, the system achieves improved linearity without the complexity and power consumption of analog correction circuits, leveraging the flexibility and efficiency of digital processing
Data Source
AI summary
A radio frequency modulator based on direct frequency/phase modulation of output signal of a controllable oscillator (724) that is a part of a phase locked loop (PLL) provides a direct modulator that is able to operate over a wide frequency range with a flat frequency response. A modulation signal is digitally processed (721, 730) before injection to a high-pass path of a direct modulator. Applicability of digital signal processing is based on the fact that the modulation signal is a base band signal. Therefore, the modulation signal (702) occupies such a band in the frequency domain so that a sufficient ratio of a sampling rate to an upper edge frequency of the modulation signal can be achieved. Digital processing is used for compensating an effect of non-flat high-pass PLL transfer function and/or to perform pre-distortion of the input signal of a controlled oscillator to compensate an effect of non-linearity of a controlled oscillator.