Listing includes: 

• AD9959 DDS Shield Board
• OLED Display (included with the DDS Shield)
• Clock Source TCXO (included with the DDS Shield)

DDS AD9959 RF Unit support control from PC via Serial Port Commands

We recommend to use RF Amplifier and Low Pass Filter with our DDS Shield Boards:

• RF Amplifier LNA 8-2000 MHz, GAIN = 20 dB, P = +20 dBm + LDO MMIC MRFA89 SOT-89
  https://www.ebay.com/itm/184629327037
  
  
• Low-Pass Filter LPF 7th Order Elliptical 1-1000Mhz 3.5 7 14 28 144 433MHz etc.
  https://www.ebay.com/itm/184877243792

Key Benefits: 

• Convenient and fast control with an encoder.
• 4 synchronized DDS channels 225MHz @ up to 600 MSPS
• Low harmonics no more than -60 dBc. An output RF transformer is used for the correct operation of the current mirror.
• Small spurs.
• 4 layer board. Signal lines TOP and Bottom, inner layers Ground and Power.
• RF Unit supports control from PC via Serial Port Commands. List of Commands presented below
• Low Noise LDO Stabilizers.
• Separate power supply for all analog and digital lines (1.8V and 3.3V), 5 pcs IC voltage stabilizers are used. Additionally, there is an RF Ferrite bead interchange.
• High-speed decoupling Level converter and TTL 5V matching.

Types of possible reference oscillators (choose one of them in the selector):

1. XO – Crystal 25 MHz 20 ppm internal oscillator with PLL up to 600 MHz.
2. TCXO – 40MHz (Supports 10 – 50 MHz) 1 ppm external oscillator PLL up to 600 MHz.
3. REF CLK IN – external reference clock input, up to 600 MHz. (this source is NOT INCLUDED).

Features: 

• At the output of each channel is a transformer to reduce even harmonics.
• Additionally balancing transformer is used for XO, TCXO and REF CLK IN options.
• Easy to connect OLED display.
• Device control with one encoder and one button.
• The synthesizer is capable to generate sine wave.
• The software allows you to select and configure the frequency of the clock generator through the user menu (without the need to recompile the program).
• Any settings can be stored in non-volatile EEPROM memory (located at Arduino Mega).
• Basic settings are applied and saved automatically.
• This shield support overclocking the AD9959 core up to 600 MHz.
• DDS AD9959 Shield has ability to generate a signal up to 225 MHz with a core overclocking up to 600 MHz (to suppress harmonics, it is recommended to  overclock the AD9959 for frequencies above 200 MHz).

Phase Noise

This parameter is very important and interesting for those who buy DDS.
Since the intrinsic phase noise of DDS is obviously less than that of PLL generators, the final value is highly dependent on the clock source. In order to achieve the values stated in the datasheet on AD9959, when designing our DDS AD9959 Arduino Shield, we strictly adhered to all recommendations from Analog Devices: PCB layout in 4 layers, separate power supply of all 4 power lines (3.3 V digital, 3.3 V analog, 1.8 V digital, and 1.8 V analog). Therefore, when buying our DDS AD9959 Arduino Shield, You can focus on the data from the datasheet on the AD9959.

Figure 18 shows the noise level when using the built-in PLL in DDS. The PLL multiplies the frequency of a 25 MHz generator by 20 times. We use a frequency – 40 MHz (x12 Multiplier) or 50 MHz (x10 Multiplier) from TCXO which gives even more stability.

And figure 16 shows the noise level when using an external reference clock 500 MHZ, with the PLL off.

Comparing these two plots, for example, for Fout = 40.1 MHz and the internal PLL turned on at 10 kHz carrier offset, the phase noise level is -127 dBc @ 10 kHz. And with the PLL off and using external clocking, the phase noise is 155 dBc @ 10kHz. That is, when using an external clock phase noise by 28 dBc better (lower).

For the same frequency Fout = 40.1 MHz, and the internal PLL turned on at 1 MHz carrier offset, the phase noise level is -130 dBc @ 1 MHz. And with the PLL off and using external clocking, the phase noise is 160 dBc @ 1 MHz. That is, when using an external clock phase noise by 30 dBc better (lower).

Conclusion: when using external clocking, You can get much lower phase noise than using the built-in PLL. But do not forget that in order to achieve such results, increased requirements are put forward to the external generator.

OLED Display Menus: