With the rapid development of digital technology, digital control method from a reference frequency source to produce a variety of frequency technology, that is, direct digital frequency synthesis (DDS) technology sudden emergence. US AD company introduced the highly integrated frequency synthesizer AD9850 DDS technology is one of the typical products.

The AD9850 uses the first locust CMOS process, its power consumption is only 155mW at 3.3V power supply, extended industrial temperature range of -40 ~ 80 ℃, 28 feet SSOP surface package form. AD9850 pin arrangement shown in Figure 1, Figure 2 for the composition of the block diagram. Figure 2 in the middle of the dotted line is a complete programmable DDS system, the outer dotted line contains the AD9850's main component.There are many electronic components distributors for supply.

The AD9850 includes programmable DDS systems and high-speed comparators for frequency synthesis of all-digital programming. Programmable DDS system is the core of the phase accumulator, which consists of an adder and an N-bit phase register, N is generally 24 to 32. For each external reference clock, the phase register is incremented by step M. The output of the phase register is added to the phase control word and can be entered on the sine lookup table address. The sine lookup table contains the digital amplitude information for a sine wave period, and each address corresponds to a phase point in the range of 0 ° to 360 ° in the sine wave. The lookup table maps the phase information of the input address to a sine wave amplitude signal, and then drives the DAC to output the mode amount.

Phase register every 2N / M external reference clock and then return to the initial state once, the phase of the sine query table each consumer goods a cycle also returned to the initial position, so that the entire DDS system output a sine wave. The output sine wave period To = Tc2N / M, the frequency fout = Mfc / 2N, Tc, fc are the cycle and frequency of the external reference clock respectively.

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