What is the purpose of a low-pass filter used at the output of a digital-to-analog converter?
The correct answer is C: Remove spurious sampling artifacts from the output signal. The purpose of a low-pass filter used at the output of a digital-to-analog converter (DAC) is to remove spurious sampling artifacts from the output signal. The filter removes high-frequency components created by the sampling process.
When a DAC converts digital samples to analog, it creates a stepped waveform. This stepped waveform contains high-frequency components (harmonics and aliasing artifacts) at multiples of the sampling frequency. The low-pass filter removes these unwanted high-frequency components, leaving only the desired signal. The filter's cutoff frequency is typically set just above the highest desired signal frequency but well below the sampling frequency. This is essential for clean analog output from digital systems.
Exam Tip
DAC output filter = Remove sampling artifacts. Remember: A low-pass filter at the DAC output removes spurious high-frequency components created by the digital-to-analog conversion process.
Memory Aid
"**D**AC **F**ilter = **R**emove **S**ampling **A**rtifacts (think 'DF = RSA')"
Real-World Application
Your digital signal generator uses a DAC to create analog waveforms. The DAC output is a stepped waveform containing high-frequency artifacts from the sampling process. A low-pass filter after the DAC removes these unwanted high frequencies, leaving a clean, smooth analog signal. Without this filter, the output would contain unwanted harmonics and noise.
FCC Part 97.3Key Concepts
Why Other Options Are Wrong
Option A: Incorrect. The filter doesn't lower input bandwidth to increase resolution. It filters the output to remove unwanted frequencies, not change input characteristics.
Option B: Incorrect. The filter doesn't remove out-of-sequence codes from the input. It removes high-frequency artifacts from the DAC output signal.
Option D: Incorrect. Not all options are correct. Only removing spurious sampling artifacts is the purpose of the DAC output filter.
题目解析
The correct answer is C: Remove spurious sampling artifacts from the output signal. The purpose of a low-pass filter used at the output of a digital-to-analog converter (DAC) is to remove spurious sampling artifacts from the output signal. The filter removes high-frequency components created by the sampling process. When a DAC converts digital samples to analog, it creates a stepped waveform. This stepped waveform contains high-frequency components (harmonics and aliasing artifacts) at multiples of the sampling frequency. The low-pass filter removes these unwanted high-frequency components, leaving only the desired signal. The filter's cutoff frequency is typically set just above the highest desired signal frequency but well below the sampling frequency. This is essential for clean analog output from digital systems.
考试技巧
DAC output filter = Remove sampling artifacts. Remember: A low-pass filter at the DAC output removes spurious high-frequency components created by the digital-to-analog conversion process.
记忆口诀
**D**AC **F**ilter = **R**emove **S**ampling **A**rtifacts (think 'DF = RSA')
实际应用示例
Your digital signal generator uses a DAC to create analog waveforms. The DAC output is a stepped waveform containing high-frequency artifacts from the sampling process. A low-pass filter after the DAC removes these unwanted high frequencies, leaving a clean, smooth analog signal. Without this filter, the output would contain unwanted harmonics and noise.
错误选项分析
Option A: Incorrect. The filter doesn't lower input bandwidth to increase resolution. It filters the output to remove unwanted frequencies, not change input characteristics. Option B: Incorrect. The filter doesn't remove out-of-sequence codes from the input. It removes high-frequency artifacts from the DAC output signal. Option D: Incorrect. Not all options are correct. Only removing spurious sampling artifacts is the purpose of the DAC output filter.
知识点
DAC output filter, Low-pass filter, Sampling artifacts, Anti-aliasing
Verified Content
Question from official FCC Extra Class question pool. Explanation reviewed by licensed amateur radio operators.