DIY function generator design - Page 1
Forum section: electronics / projects

author: Dhanushka
author_rank: Regular Contributor
timestamp: April 18, 2019, 08:04:02 am
content: 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 this2. 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.

author: MarkF
author_rank: Super Contributor
timestamp: April 18, 2019, 09:22:52 am
content: 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/#msg2325642Sine, triangle, square, sine sweep, triangle sweep and PWM waveforms. Some generated in combination with pic18F2550.Prototype:Actually, updated circuit here.

author: bloguetronica
author_rank: Frequent Contributor
timestamp: April 18, 2019, 01:58:12 pm
content: 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.htmlYou 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 50loads, rail-to-rail if required.Kind regards, Samuel Lourenço

author: HB9EVI
author_rank: Frequent Contributor
timestamp: April 18, 2019, 07:33:19 pm
content: +1 for the AD9834the 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.

author: Kleinstein
author_rank: Super Contributor
timestamp: April 18, 2019, 08:05:15 pm
content: 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.

author: HB9EVI
author_rank: Frequent Contributor
timestamp: April 18, 2019, 08:12:12 pm
content: the AD9850 is a good choice to get the whole shortwave area covered; but I fast gave up on those chinese modules; a very poor design; it's really worth doing your own PCB and LPF

author: Dhanushka
author_rank: Regular Contributor
timestamp: April 19, 2019, 06:17:23 pm
content: Thanks for all comments and resources you provided.Also, could you please let me know that can I use the AD9833 Arduino library to control AD9834?Thank you.