What type of frequency synthesizer circuit uses a phase accumulator, lookup table, digital-to-analog converter, and a low-pass anti-alias filter?
The correct answer is A: A direct digital synthesizer. A direct digital synthesizer (DDS) uses a phase accumulator, lookup table, digital-to-analog converter (DAC), and a low-pass anti-alias filter. This is the architecture of a DDS system.
In a DDS, the phase accumulator generates a digital phase value that increments at each clock cycle. This phase value is used to address a lookup table (which contains amplitude values representing a sine wave). The lookup table outputs digital amplitude values that are converted to analog by the DAC. The low-pass filter removes aliasing artifacts and smooths the output. DDS systems provide precise frequency control and are commonly used in modern radio equipment for frequency synthesis. They can generate clean sine waves with excellent frequency resolution.
Exam Tip
Phase accumulator + lookup table + DAC = DDS. Remember: A direct digital synthesizer uses a phase accumulator, lookup table, digital-to-analog converter, and low-pass filter.
Memory Aid
"**D**DS = **D**igital **P**hase **A**ccumulator, **L**ookup, **D**AC, **F**ilter (think 'DDS = DPLDF')"
Real-World Application
Your modern transceiver uses a DDS for frequency generation. The phase accumulator creates a digital phase ramp, the lookup table converts phase to amplitude values, the DAC converts these to analog, and the filter removes aliasing. This provides precise, stable frequency generation that can be controlled digitally with excellent resolution.
FCC Part 97.3Key Concepts
Why Other Options Are Wrong
Option B: Incorrect. A hybrid synthesizer might combine different techniques, but the specific components listed (phase accumulator, lookup table, DAC, filter) are characteristic of a DDS, not a hybrid.
Option C: Incorrect. A phase-locked loop synthesizer uses a phase detector, VCO, and reference oscillator, not a phase accumulator and lookup table.
Option D: Incorrect. A direct conversion synthesizer is not a standard term. The components described are specific to DDS architecture.
题目解析
The correct answer is A: A direct digital synthesizer. A direct digital synthesizer (DDS) uses a phase accumulator, lookup table, digital-to-analog converter (DAC), and a low-pass anti-alias filter. This is the architecture of a DDS system. In a DDS, the phase accumulator generates a digital phase value that increments at each clock cycle. This phase value is used to address a lookup table (which contains amplitude values representing a sine wave). The lookup table outputs digital amplitude values that are converted to analog by the DAC. The low-pass filter removes aliasing artifacts and smooths the output. DDS systems provide precise frequency control and are commonly used in modern radio equipment for frequency synthesis. They can generate clean sine waves with excellent frequency resolution.
考试技巧
Phase accumulator + lookup table + DAC = DDS. Remember: A direct digital synthesizer uses a phase accumulator, lookup table, digital-to-analog converter, and low-pass filter.
记忆口诀
**D**DS = **D**igital **P**hase **A**ccumulator, **L**ookup, **D**AC, **F**ilter (think 'DDS = DPLDF')
实际应用示例
Your modern transceiver uses a DDS for frequency generation. The phase accumulator creates a digital phase ramp, the lookup table converts phase to amplitude values, the DAC converts these to analog, and the filter removes aliasing. This provides precise, stable frequency generation that can be controlled digitally with excellent resolution.
错误选项分析
Option B: Incorrect. A hybrid synthesizer might combine different techniques, but the specific components listed (phase accumulator, lookup table, DAC, filter) are characteristic of a DDS, not a hybrid. Option C: Incorrect. A phase-locked loop synthesizer uses a phase detector, VCO, and reference oscillator, not a phase accumulator and lookup table. Option D: Incorrect. A direct conversion synthesizer is not a standard term. The components described are specific to DDS architecture.
知识点
Direct digital synthesizer, DDS, Phase accumulator, Lookup table, DAC
Verified Content
Question from official FCC Extra Class question pool. Explanation reviewed by licensed amateur radio operators.