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I'm making a precise, low-current current source for a bio-impedance meter using a howland current pump.

Currently the current pump is driven by a wien-bridge oscillator to produce a 1V p-p 100hz sine wave, my goal is to make it programmable by swapping this for a DDS (AD9852 tentatively). Most commercial DDS ic's are designed for telecom and other high frequency applications and have performance specs available on the MHz level, however information on performance in the low frequency domain is sparse.

SO my question is, how well do commercial DDS IC's perform at frequencies on the order of 100Hz - 1Khz? I'll be sticking an atmega or similiar MCU and will probably drive both the MCU and DDS with a 10MHz clock

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  • \$\begingroup\$ Just tried an experiment with a $4.50 prebuilt DDS module bought on eBay, the trace looks perfectly smooth on the oscilloscope down to 50 Hz. Inexpensive enough to buy one and try whether it meets your needs. \$\endgroup\$
    – Anindo Ghosh
    Jul 19, 2013 at 4:24

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100 Hz to 1 KHz really sounds like audio frequencies. I can, and have, used audio DAC's and some opamps to generate arbitrary frequency sine waves in the 20 Hz to 20 KHz range with better than -100 dB THD+N, better than 100 dB Signal to Noise, and very good frequency accuracy (limited by the crystal/oscillator that you use).

Good quality audio DAC's run just a couple of dollars. The highest quality DAC's are maybe US$3 in 1K qty. So it is not that expensive. You'll have to add some opamps to it, but those are cheap too.

You would be hard pressed to do this another way for cheaper and/or with better quality of sine wave.

You can drive the DAC from many MCU's. I did it with an FPGA, but that's because I had an FPGA handy.

I should also point out that @Anindo's comment about getting a cheap module to play around with is completely valid. That module he linked to has the ADI AD9850 on it and it might also do what you want.

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  • \$\begingroup\$ +1, Analog has outdone itself with that family of DDS chips. "Output frequency can be digitally changed (asynchronously) at a rate of up to 23 million new frequencies per second. The device also provides five bits of digitally controlled phase modulation, which enables phase shifting of its output in increments of 180°, 90°, 45°, 22.5°, 11.25°, and any combination thereof." \$\endgroup\$
    – Anindo Ghosh
    Jul 19, 2013 at 17:03
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I suspect that microcontrollers running a bit of frequency divider code have taken over most of those very low frequency applications. That's down in the audio range, have you looked at audio synthesizers as examples? You could probably just use your atmega as a DDS.

There's also this part http://www.analog.com/static/imported-files/data_sheets/AD9837.PDF

which is a low frequency DDS/Signal Generator. The specs all seem to end at 1 kHz, but it should work lower than that.

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