+/- sinusoid from AD9850 DDS chip.

[zoulzubazz]

hey,

the requirement is to generate a sinusoid about +/-1V peak to peak somewhere close to 10MHz. The AD9850 DDS chip can be used to achieve this frequency but can output only dc and upwards. Is there a way to transform the output from the DDS to a sinusoid split between + and - voltage. thanks very much.

 

[FvM]

Did you consider AC coupling the output signal (implement a first order high pass)?

 

[zoulzubazz]

thanks FvM, the ability of a cap to block DC is sort of the fundamentals. simulated this in spice and it works. this might sound daft but I don't understand the physics behind it though, how can a cap source a voltage below ground.

 

[crutschow]

A capacitor cannot pass DC, thus any signal through a capacitor must have an average DC value of 0V. This means any sinewave through a capacitor will be centered around 0V with equal plus and minus peaks to give a 0V average value.
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Since above ground (+) and below ground (-) are just voltages relative to ground a capacitor output can readily go either way. There's nothing special about "below ground" as compared to "above ground" to a capacitor.