Electronics > Projects, Designs, and Technical Stuff
DIY function generator design
Dhanushka:
I am going to design a simple DIY function generator using an AD9833 cheap 3$ module and a high bandwidth output amplifier module. Could you please tell me about the things below that I have stated.
1. Possibility to success this
2. What are the suitable cheap high bandwidth(about 10 MHz) amp modules on E bay? (That should have offset adjustments, output impedance about 50 Ohm and maximum output voltage should about +-10 V)
3. What is the best output amplifier configuration of simple non inverting or instrumentation?
I hope you give good solutions.
Thank you.
MarkF:
Spoiler alert!
I think the AD9834 is a better choice because it allows you to do amplitude control.
Go here for my design: https://www.eevblog.com/forum/projects/amplitude-modulation-of-ad9834-dds-failed-but-why/msg2325642/#msg2325642
Sine, triangle, square, sine sweep, triangle sweep and PWM waveforms. Some generated in combination with pic18F2550.
Prototype:
Actually, updated circuit here.
bloguetronica:
Hi,
As MarkF said, the AD9834 is a very good choice. And besides having amplitude control, it provides a way to cancel offset thanks to its differential output. You can see another project, based on the AD9834, on my blog (it is in Portuguese, but the automatic translation to English is good):
http://www.bloguetronica.com/2018/07/gerador-de-funcoes-gf2.html
You can find AD9834 modules cheap on eBay. With a CP2130 evaluation board (also cheap), you can make yourself a decent function generator. You may have to change or even implement a reconstruction filter. Having a 7th order, 0.01dB Chebyshev aligned low pass filter is essential. You can use a lower order one, or instead choose a Butterworth aligned one.
If you wish to have more power, you can choose an AD9102. It has all the features of the previous, but with the addition of direct amplitude and offset control (i.e. inside the chip itself), plus more waveforms at a higher sampling rate.
For the amplifier stage, definitely you'll need an high speed op-amp with a gain–bandwidth product in the order of thousands of MHz, at least, if not in the order of GHz. Choose wisely! My suggestion, you should choose the LMH6612 or similar for the output stage. Take into account that this op-amp will need to drive 50 \$\Omega\$ loads, rail-to-rail if required.
Kind regards, Samuel Lourenço
HB9EVI:
+1 for the AD9834
the AD9833 is a real minimalistic device without any nice-to-have features, also 25MHz MCLK is rather low; I overclocked the AD9834 to 80MHz without issues; about 20MHz sine with filtering is achievable.
Kleinstein:
If one does not need the triangle wave one could also consider modules with an AD9850. These are faster and include the clock and often a filter - though with often poor quality.
With the amplifier it depends on the needs (e.g. amplitude, frequency range). The choice could also depend on availability / possible choices.
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