Two-Point Modulation Phase Apparatus Alias Suppression
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Existing two-point modulation phase modulation apparatuses face challenges in achieving superior modulation precision for wide frequency band signals while maintaining low power consumption and simple anti-alias filter configurations, as they require high sampling frequencies or complex filter configurations to suppress alias signals without degrading noise characteristics.
Innovation Solution
The apparatus incorporates a differentiator to preprocess the digital baseband modulation signal, followed by an anti-alias filter with a narrower bandwidth than the PLL frequency band, and an adder to output the combined signal to the voltage controlled oscillator, maintaining a flat frequency characteristic and suppressing alias signals effectively without increasing the sampling frequency or filter complexity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If the sampling frequency of the D/A converter is increased to suppress alias signals, then alias signal suppression improves, but power consumption increases
Solution Approach 1:
The differentiator circuit performs preliminary processing on the digital baseband modulation signal before it reaches the D/A converter. By differentiating the signal in advance, the spectral characteristics are modified such that alias components are naturally suppressed after D/A conversion, eliminating the need to increase sampling frequency and thus avoiding increased power consumption.
Solution Approach 2:
The differentiator acts as an intermediary processing stage between the digital baseband modulation signal and the D/A converter. This intermediate processing modifies the signal spectrum so that when aliasing occurs during D/A conversion, the aliased components fall into frequency ranges that are subsequently filtered out by the anti-alias filter, achieving suppression without higher sampling rates.
2Adaptability or versatility
If the bandwidth of the anti-alias filter is widened to pass wide frequency band signals, then signal bandwidth coverage improves, but alias signal suppression deteriorates
Solution Approach 1:
The differentiator circuit performs preliminary spectral shaping on the digital baseband modulation signal before D/A conversion. This preliminary action ensures that when the anti-alias filter with narrow bandwidth processes the signal, the desired frequency components are already positioned in a way that allows effective alias suppression while maintaining wide frequency band adaptability.
Solution Approach 2:
The differentiator changes the spectral parameters of the digital baseband modulation signal by performing differentiation in the time domain, which corresponds to multiplying by frequency in the frequency domain. This parameter transformation allows the signal to be processed by a narrow-band anti-alias filter while still achieving wide frequency band coverage after PLL processing.
3Measurement precision
If the PLL frequency bandwidth is made wide to improve modulation precision, then modulation precision improves, but noise characteristics deteriorate
Solution Approach 1:
The modulation process is segmented into two independent paths: one path handles low-frequency components through the PLL with narrow bandwidth to maintain good noise characteristics, while the other path handles high-frequency components through the differentiator-D/A converter-anti-alias filter chain. The two paths are then combined to achieve wide frequency band modulation precision without sacrificing noise performance.
Solution Approach 2:
The differentiator-D/A converter-anti-alias filter chain acts as an intermediary path that handles the high-frequency components of the modulation signal. This intermediary path allows wide frequency band signals to be processed without requiring the PLL to have wide bandwidth, thus preserving the PLL's noise characteristics while achieving wideband modulation precision through combination with the PLL output.
Data Source
AI summary
There provides a two-point modulation phase modulation apparatus capable of obtaining an RF phase modulation signal of superior modulation precision with low power consumption and a simple configuration even in the event of inputting a wide band baseband modulation signal. A differentiator (21) of the opposite characteristics to the attenuation characteristics of anti-alias filter (22) is provided at the front stage of a D/A converter (6). As a result, it is possible to sufficiently suppress an alias signal without raising the sampling frequency of the D/A converter (6) (i.e. low power consumption) using an anti-alias filter (22) of a simple configuration (i.e. low cost) with a low order for a narrower bandwidth than a PLL modulation frequency bandwidth, and it is possible to obtain an RF phase modulation signal where the entire frequency band of input digital baseband modulation signal (S1) is reflected in a superior manner.