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# AD9786 maximum analog output frequency

Hi,

What is the maximum analog output frequency we can generate from AD9786 DAC in 1x,2x,3x and 4x interpolation modes?

Max input data rate : 200Msps.

Max output update rate : 500Msps.

How to determine the max output frequency from above data?

Regards,

Surendra

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• the answer is "it depends"

with max input datarate of 200MSPS, the max BW without aliasing is 100MHz. Minus the interpolation filter pass BW, which is typically 80%, assuming interpolation is used.

Note that, with Fdac=500MSPS, a 2x interpolation would set the datarate at the interpolation filter input to 250MSPS. datarate=Fdac/interpolation. datarate with 4x interpolation is 125MSPS, and so on.

Regarding max frequency. The AD9786 has an NCO, which is a digital mixer. So you can up-convert the baseband signal to higher frequency. Then the limitation is only the DAC sampling rate (Fdac=500MSPS in this case).

So Fout = Fnco * Fsignal

Note however, that above Fdac/2, the signal will both generate image and alias tones. So for example, with Fdac=500MHz and Fsignal=100Mhz, you will also see an image tone at Fdac-Fout and an alias tone at Fdac*N+Fout which would repeat across the spectrum.

This is due to nyquist rate and sampling theory.

So the answer is "it depends". You can very well use the aliases and/or image tones of the tone you generate, move it around the spectrum using the NCO, and filter around it.

The only limitation is, ultimately the bandwidth of the signal. so BWmax = datarate/2.

• the answer is "it depends"

with max input datarate of 200MSPS, the max BW without aliasing is 100MHz. Minus the interpolation filter pass BW, which is typically 80%, assuming interpolation is used.

Note that, with Fdac=500MSPS, a 2x interpolation would set the datarate at the interpolation filter input to 250MSPS. datarate=Fdac/interpolation. datarate with 4x interpolation is 125MSPS, and so on.

Regarding max frequency. The AD9786 has an NCO, which is a digital mixer. So you can up-convert the baseband signal to higher frequency. Then the limitation is only the DAC sampling rate (Fdac=500MSPS in this case).

So Fout = Fnco * Fsignal

Note however, that above Fdac/2, the signal will both generate image and alias tones. So for example, with Fdac=500MHz and Fsignal=100Mhz, you will also see an image tone at Fdac-Fout and an alias tone at Fdac*N+Fout which would repeat across the spectrum.

This is due to nyquist rate and sampling theory.

So the answer is "it depends". You can very well use the aliases and/or image tones of the tone you generate, move it around the spectrum using the NCO, and filter around it.

The only limitation is, ultimately the bandwidth of the signal. so BWmax = datarate/2.

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