{"id":8324,"date":"2024-04-13T20:32:40","date_gmt":"2024-04-13T15:02:40","guid":{"rendered":"https:\/\/nuclearrambo.com\/wordpress\/?p=8324"},"modified":"2024-10-03T14:56:45","modified_gmt":"2024-10-03T09:26:45","slug":"diy-stm32-and-ad9913-signal-generator-board","status":"publish","type":"post","link":"https:\/\/nuclearrambo.com\/wordpress\/diy-stm32-and-ad9913-signal-generator-board\/","title":{"rendered":"DIY STM32 and AD9913 signal generator board"},"content":{"rendered":"\n

The AD9913 direct digital synthesizer works as a digital waveform synthesizer that can generate signals with very precise resolution. When it comes to radio receivers, the AD9913 with <0.05Hz resolution can be used as a beat frequency oscillator for SSB demodulation. As compared to the AD9833<\/a> DDS, the AD9913 has an internal PLL that can internally generate higher sampling rates. This allows us to use a lower-frequency external oscillator. Additionally, the AD9913 is a very low power chip, and it takes very little power. Therefore, this chip generates very little heat.<\/p>\n\n\n\n

This circuit generates clean sine wave signals or it may also generate signals based on a frequency ramp profile. ‘Frequency profile’ is a very good feature when it comes to generating any frequency varying waveforms. Additionally, frequency profiles can also allow frequency hopping often used in wireless communication systems. The DDS finds itself in many applications but we won’t dive into those in this article. The main purpose of this article is to show the board design and a basic firmware that is able to generate any frequency in the given limits. The article does not go too deep into the theory. I have simply attempted to demonstrate the “top level” working of this board with a few tips here and there to get your design working.<\/p>\n\n\n\n

The schematic<\/h2>\n\n\n\n

The hardware is designed with help of the reference design provided by Analog devices. It uses three linear voltage regulators: one for powering the microcontroller, one for analog signal conditioning and one for the digital signals controlling the DDS. I could have used a signal regulator for the DDS but I went for three for keeping the output signal generation noise free. <\/p>\n\n\n\n

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AD9913 and STM32F103 board block diagram<\/figcaption><\/figure>\n\n\n\n

The power section<\/h3>\n\n\n\n

As described above, I used 3 voltage regulators with 2.6V to 11V input range with part number ADP3334<\/a>. Although quite expensive, I wanted to consume the stock of these regulators that I already own. Feedback resistors at the output set the output voltage of the regulator. <\/p>\n\n\n\n

You can either calculate the feedback resistor network on your own or refer the datasheet and use the suggested values. <\/p>\n\n\n\n

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I went the easy route and used the suggested resistor values and design my schematic as shown below.<\/p>\n\n\n\n

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ADP3334 schematic in Altium Designer<\/figcaption><\/figure>\n\n\n\n

The simplest schematic suggested by Analog devices allows you to skip the input capacitors and only have a single 1uF capacitor at the output. For better noise rejection and stability, I chose to add the input and output capacitors. Additionally, I also added a LC filter at the output for further noise filtering. Based on your choice, you can decide to bypass it with a 0 Ohm resistor.<\/p>\n\n\n\n

There is another regulator that generates analog 1V8 supply for the DDS core and that’s not shown here.<\/p>\n\n\n\n