PLL FM Circuit Using Dual Digital-Analog VCO Modulation
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Solution Overview
Problem
Traditional FM transmitters with phase-locked loops face challenges in high power consumption, increased chip area due to complex high-precision digital-to-analog converter (DAC) design, and higher output noise gain from the voltage-controlled oscillator (VCO), which complicates frequency modulation circuits.
Innovation Solution
A frequency modulation circuit with a phase-locked loop and voltage-controlled oscillator (VCO) that uses a dual-modulation approach, combining digital and analog modulation signals to control the VCO, reducing the complexity of the DAC design and noise gain by using switched capacitor arrays and sigma-delta modulation, thereby optimizing power consumption and chip area.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a high-precision digital-to-analog converter (DAC) is used in the frequency modulation circuit, then the frequency resolution is improved, but the chip area and manufacturing complexity increase
Solution Approach 1:
The frequency modulation range is divided into multiple segments, with each segment controlled by a separate DAC channel. Instead of using one high-precision DAC to cover the entire frequency range, multiple lower-precision DACs work in parallel, each handling a specific frequency segment. This segmentation reduces the precision requirement for each individual DAC while maintaining overall frequency resolution.
Solution Approach 2:
The patent transitions from a single-dimensional frequency control approach to a multi-dimensional approach by introducing multiple DAC channels that control different frequency segments. This dimensional expansion allows the system to achieve high frequency resolution through coordinated control of multiple lower-precision components rather than relying on a single high-precision DAC.
2Object-affected harmful factors
If the voltage-controlled oscillator (VCO) output noise gain is reduced, then the output noise is improved, but the frequency modulation range is reduced
Solution Approach 1:
The frequency modulation range is segmented across multiple DAC channels, allowing the system to achieve wide frequency modulation range through coordinated control of multiple channels. Each channel operates with optimized noise characteristics for its specific frequency segment, enabling the overall system to maintain low output noise while covering a broad frequency range.
Solution Approach 2:
The patent implements dynamic switching between different DAC channels based on the desired frequency modulation requirements. By dynamically allocating which DAC channel controls which frequency segment, the system can optimize noise performance for different operating conditions while maintaining the ability to access the full frequency modulation range when needed.
3Use of energy by moving object
If the DAC precision is reduced, then the chip area and power consumption are reduced, but the frequency resolution is degraded
Solution Approach 1:
The frequency control task is segmented across multiple DAC channels, allowing each DAC to operate at lower precision levels. This segmentation enables the use of simpler, lower-power DAC designs while maintaining overall high frequency resolution through the coordinated operation of multiple channels. Each DAC consumes less power individually, and the combined system achieves the required frequency resolution.
Solution Approach 2:
Instead of using a single high-precision DAC, the patent employs multiple copies of lower-precision DACs working in parallel. Each DAC copy handles a specific portion of the frequency control task, reducing the precision requirements for each individual copy. This copying approach allows the system to achieve high frequency resolution through the collective output of multiple simpler DAC components.
Data Source
AI summary
A frequency modulation circuit can include: a modulation circuit configured to generate a digital modulation signal and an analog modulation signal according to an input signal of the frequency modulation circuit; and a phase-locked loop having a voltage-controlled oscillator configured to receive a reference frequency, and to modulate a frequency of an output signal of the voltage-controlled oscillator according to the analog modulation signal and the digital modulation signal.