DDS generator. Scheme, description

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ENCYCLOPEDIA OF RADIO ELECTRONICS AND ELECTRICAL ENGINEERING
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DDS generator. Encyclopedia of radio electronics and electrical engineering

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Encyclopedia of radio electronics and electrical engineering / Measuring technology

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Often, in amateur radio practice, a simple functional DDS (Direct Digital Frequency Synthesis) generator is needed. To get a specific frequency...

I have developed a simple on-chip sine generator from Analog Devices AD9832. The circuit generated a sinusoid from 0.005 to 12 MHz with a step of 0.005 Hz. But while I was waiting for the AD9832 chip to arrive, a simple DDS generator was developed using an AT90S2313 microcontroller and a resistive matrix.

The generator is controlled via RS232 by a small Windows program and can generate the following waveforms: sine, triangle, sawtooth, rectangle in the frequency range from 0.07 Hz to 200-300 kHz in 0.07 Hz steps (depending on the quartz used).

DDS generator. DDS generator program

I don't want to go into the details of how a DDS generator works. The source code is attached, it is very simple and easy to understand.

DDS generator

The circuitry of the device is also simple, it has 4 main parts: a voltage regulator, an RS232 transceiver, an AT90S2313P microcontroller and a resistive matrix (R2R). Matrix R2R is connected to the pins of MK portB, thus. forming a simple DAC and allowing you to get 256 voltage levels.

The MAX603 is also used to implement generator on/off functions via the RS232 serial interface (DTR signal). When you close the generator program on the computer, then the DDS generator is turned off by the received signal, i.e. saving batteries.

(click to enlarge)

The program code is written in assembler. The code is small and the main loop is very fast. This is the heart of the generator code. The main loop contains 7 lines of code. The rest of the code is waveform tables and communication code.

The phase accumulator is 24 bits and is used to set the resolution.

The maximum generated frequency and resolution also depends on the crystal used:
Resolution = Crystal frequency / 150994944
fOut = Accumulator * Resolution
In my case, the quartz was at 11.059200 MHz, so the resolution was 0.073242188 Hz.
In order to get an output frequency of 1 kHz, it is necessary to write the value 0x003556 (13654 dec) into the phase accumulator. This will give 1000.048835 Hz. Quite sufficient accuracy for a radio amateur.

The communication code of the program is also simple and allows you to write values to the phase accumulator and select the type of waveform.

DDS generator. Oscillator Waveforms: Sine, Rectangle, Saw

Download assembler source and Windows program

Publication: cxem.net

See other articles Section Measuring technology.

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