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Connecting High speed DAC to Mixers in Digital modulation scheme

Hi,

In digital IQ modulation based systems, the High speed DACs are connected directly to mixers by skipping IQ modulators.

In this case can we use same circuitry (which are used in connecting DACs to Modulators) to connect DACs to Mixers (Passive reconstruction filter circuit) or should we add any additional circuitry. Will the DAC seamlessly connect to the Mixer or should we do any power conversion with VGA or step attenuators.

The DAC used - AD9746

Mixer - ADL5801.

(DAC o/p frequency - 30 MHz)

Thanks in advance

Parents
  • In a typical signal chain which you describe, in which the DAC drives a mixer (not an IQMod)  the baseband I and Q channels must be modulated onto the carrier at low IF either in the DAC, or in the digital engine previous to the DAC. Since the AD9746 does not have any IQModulation capability (we have other DACs that do this, AD9122 and AD9788 as examples) I'm assuming that you must be doing the IQMod in the digital domain previous to the DAC. Can you confirm? If this is true, I'm curious why you are choosing a dual DAC like the AD9746 to drive a mixer, what is the other DAC channel doing? Also, since the AD9746 can only generate somewhat low IF frequencies, I think you are going to have to deal with the undesired sideband at LO-IF, where if you used the analog IQMod approach after the dual DAC, this image would be supressed by at least 40dB with no compensation. Please let me know if I am misunderstanding anything

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  • In a typical signal chain which you describe, in which the DAC drives a mixer (not an IQMod)  the baseband I and Q channels must be modulated onto the carrier at low IF either in the DAC, or in the digital engine previous to the DAC. Since the AD9746 does not have any IQModulation capability (we have other DACs that do this, AD9122 and AD9788 as examples) I'm assuming that you must be doing the IQMod in the digital domain previous to the DAC. Can you confirm? If this is true, I'm curious why you are choosing a dual DAC like the AD9746 to drive a mixer, what is the other DAC channel doing? Also, since the AD9746 can only generate somewhat low IF frequencies, I think you are going to have to deal with the undesired sideband at LO-IF, where if you used the analog IQMod approach after the dual DAC, this image would be supressed by at least 40dB with no compensation. Please let me know if I am misunderstanding anything

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