Demodulator Signal Path Split for Varactor Linearity and Noise Control
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Existing demodulators face deterioration in demodulation performance due to nonlinearity of input amplitude-frequency characteristics of variable capacitive elements in frequency variable oscillators, leading to distortion and reduced Signal-to-Noise and Distortion Ratio (SNDR), and this issue is exacerbated by noise when using Auto Gain Control (AGC) to limit signal amplitude.
Innovation Solution
A demodulator configuration that includes a phase difference signal generator, low-resolution A/D and D/A converters, control signal generators, and a frequency variable oscillator, which processes signals to operate within the linear region of varactor capacitance, reducing distortion and noise influence by generating control signals with lower amplitudes and using ADPLL or analog PLL circuits for phase locking.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If AGC function is implemented to limit amplitude of analog input signal, then distortion due to nonlinearity is avoided, but signal amplitude with respect to noise floor is decreased causing deterioration in reception performance
Solution Approach 1:
The control signal is segmented into two parts: a first control signal with limited amplitude (processed through low-resolution A/D and D/A converters) and a second control signal with high resolution (generated by ADPLL). This segmentation allows each signal to handle different aspects of frequency control, with the first signal preventing nonlinearity distortion and the second maintaining signal amplitude for noise resistance.
Solution Approach 2:
Low-resolution A/D and D/A converters act as intermediaries to process the first control signal, transforming it into a form that limits amplitude to avoid nonlinearity while preserving the essential frequency control function. This intermediary processing resolves the contradiction by mediating between the need for amplitude limitation and noise resistance.
2Adaptability or versatility
If amplitude of analog control signal is increased, then frequency control range is improved, but nonlinearity of variable capacitive element causes distortion in VCO signal
Solution Approach 1:
The frequency control function is segmented between two control signals: the first control signal handles amplitude-limited frequency adjustments (avoiding nonlinearity), while the second control signal provides high-resolution frequency tuning. This segmentation enables broad frequency control range without entering the nonlinear region of the variable capacitive element.
Solution Approach 2:
The invention changes the resolution parameter of the control signals differently for each function: the first control signal uses low resolution (1-3 bits) to limit amplitude, while the second control signal uses high resolution (12-16 bits) for precise frequency control. This parameter differentiation resolves the contradiction between control range and linearity.
3Manufacturing precision
If resolution of A/D converter is reduced, then distortion from nonlinearity is reduced, but quantization noise increases
Solution Approach 1:
The control function is segmented into two parallel paths: one using low-resolution A/D conversion for amplitude-limited frequency control (reducing nonlinearity distortion), and another using high-resolution digital processing (ADPLL) for precise frequency tracking. This segmentation allows each path to optimize for its specific function, minimizing overall distortion and noise.
Solution Approach 2:
The low-resolution A/D converter acts as an intermediary that deliberately introduces quantization but limits its impact by constraining the signal amplitude to the linear region. The quantization noise is confined to a controlled range and does not propagate to degrade overall system performance.
Data Source
AI summary
There is provided a demodulator that makes it possible to reduce or avoid deterioration in demodulation performance due to nonlinearity of input amplitude-frequency characteristics of a variable capacitive element included in an analog control signal input section of a frequency variable oscillator, while suppressing an influence of noise. The demodulator includes: a low-resolution A/D converter that performs analog-digital conversion of a first phase difference signal to generate a second phase difference signal that is digital; a low-resolution D/A converter that performs digital-analog conversion of the second phase difference signal to generate a third phase difference signal; an analog subtractor that subtracts the third phase difference signal from the first phase difference signal to generate a first control signal; an ADPLL that generates a second control signal; and an FVO that generates the oscillation signal on the basis of the first control signal and the second control signal.