Direct Digital Synthesizer (DDS) is actually a frequency divider: divide the system clock (SYSTEM CLOCK) by programming the frequency control word to generate the required frequency. DDS has two outstanding features. On the one hand, DDS works in the digital domain. Once the frequency control word is updated, the output frequency will change accordingly and its frequency hopping rate is high. Higher), high frequency resolution. The internal structure of DDS is mainly divided into 3 parts: phase accumulator, phase amplitude conversion, digital-to-analog converter (DAC).
Features:
The module can output sine wave and square wave, 2 sine wave and 2 square wave output.
AD9850: 0-40MHz
AD9851: 0-70MHz
After the frequency is 20-30MHz, the harmonic becomes larger and larger, and the waveform will become more and more unclean.
Square wave: 0-1MHz
Uses a 70MHz low-pass filter to make the waveform's SN ratio better
10-bit DAC, 32-bit frequency control word
The comparator's reference input voltage is generated by a variable resistor. Adjusting this resistor can get different duty cycle square waves.
Note: In the case of outputting a sine wave, connect to the IO port of the square wave output and directly adjust
The blue potentiometer can output a square wave.
AD9850 module uses 125MHz active crystal, AD9851 module uses 30MHZ active crystal
AD9850 and AD9851 main differences:
The clock frequency of AD9850 is up to 125MHz, and the clock frequency of AD9851 is up to 180MHz (30MHz * 6). The highest output frequency AD9851 is higher than AD9850.
AD9850 does not have a 6 octave, AD9851 does
