anyone can advice me?
i'm now doing a project of signal generator by using DDS technique.
i've used PIC 16F877 with 24MHz clock.
analog output waveform using R-2R ladder network.
but the output waveform that i got is not smooth at 40KHz and above.
one thing i'd like to know is how to get the smoother 100KHz analog output waveform.
thanks in advance.
Hi,
I hope you are using a LPF network after the DAC. To get it to 100kHz and also get 40kHz is slightly difficult. What is the resolution you expect.
B R M
What is your DAC sample rate? I'm guessing it's slower than 24MHz. As brmadhukar suggests, you need a low pass filter after the DAC to reject sampling images (they look like stair steps on an oscilloscope). Design a filter that passes the frequencies you want, and strongly attenuates the sample rate and higher.
Thanks for your advise.
I've used 8-bits DAC & 24-bits phase accumulator wordlength.
How much resolution will be got the output analog waveform to be smooth?
Your third sentance is unclear, so this may not answer your question.
An 8-bit DAC generates quantization noise approximately 48 dB below the desired sinewave. If you build a very good low-pass filter, the sinewave will look beautiful and smooth on an ordinary oscilloscope, however the quantization noise will be easily visible on a spectrum analyzer.