Dual-Path PLL Radio Transmitter for Flat Frequency Response
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Solution Overview
Problem
Existing radio transmitters using PLLs with VCXO and VCO modulation paths face challenges in maintaining a flat frequency response and stability, especially across varying temperatures, due to differences in frequency responses between the two paths.
Innovation Solution
A radio transmitter design that splits the modulating signal into two paths, one for the VCO and one for the PLL, with adjustable frequency division ratios and phase/frequency-response adjustments to ensure balanced modulation across a wide frequency range, thereby minimizing frequency variation and maintaining a flat frequency response.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If VCXO is used to modulate the reference-frequency signal for wide frequency range modulation, then modulation coverage from DC to several kHz is achieved, but frequency variation increases and frequency response balance deteriorates
Solution Approach 1:
The patent divides the single modulation path into two separate paths: one using VCO for frequency modulation and another using VCXO with frequency division ratio variation. Each path handles specific frequency ranges and characteristics, allowing the system to achieve wide frequency coverage while maintaining frequency stability through coordinated operation of both segments.
2Adaptability or versatility
If VCXO-based modulation path is used, then wide frequency range modulation is achieved, but frequency-response balance between VCO and VCXO paths deteriorates
Solution Approach 1:
The patent dynamically adjusts the frequency division ratio in the VCXO-based path and applies frequency-response adjustment to modify the characteristics of the second modulating signal. This parameter change allows the VCXO path to compensate for its inherently different frequency response compared to the VCO path, achieving balanced overall frequency response across the wide modulation range.
3Measurement precision
If frequency division ratio is varied in PLL path, then modulation accuracy is improved, but device complexity increases
Solution Approach 1:
The patent integrates the frequency division ratio variation function within the existing PLL circuitry, allowing the same PLL structure to serve multiple purposes: maintaining frequency synthesis functionality while enabling precise modulation through dynamic division ratio changes. This multi-functionality approach improves modulation accuracy without proportionally increasing device complexity.
Data Source
AI summary
A radio transmitter includes a signal processing circuit splitting a basic modulating signal into first and second modulating signals and outputting the first and second modulating signals. A PLL decides a fundamental wave. A VCO forms a portion of the PLL and modulates the fundamental wave decided by the PLL in accordance with a voltage of the first modulating signal outputted from the signal processing circuit. A PLL circuit forms a portion of the PLL and varies a frequency division ratio to modulate the fundamental wave decided by the PLL in accordance with the second modulating signal outputted from the signal processing circuit.