AD9954 DDS and AD8349 IQ-mod

[7rots51]

ad9954

AD9954 is AVDD refrenced at DAC output ,and AD8349 is AGND refrenced at input of I and Q signals.

AD8349 need only 400mV dc bias at input.

How to couple AD9954 DDS and AD8349 I-Q-Modulator in differential form?

I want to FSK modulation.

 

[boy]

ad9954 dds

If you need only FSK, you dont need AD8349 I-Q-Modulator. You will need only an upconverter. However, if you still want to use AD8349 I-Q-Modulator, you just need to to connect the output of AD9954 DDS to either I or Q input of AD8349 I-Q-Modulator. They are both differential so you dont need any transformer.

 

[7rots51]

ad9954 transformer

I used 2 AD9954 on for I and other for Q(both are sync)

Output of AD9954 is diff and input of AD8349 are diff,

BUT the dc level of DAC output of AD9954 is around 1800mv and DC bias level needed for ad8349 is 400mv!

How can I couple them and solve the dc level problem?

I can not connect them directly because they have different dc levels.

 

[boy]

dds ad9954

Why dont you use a capacitor to block DC level output of AD9954 and bias ad8349 with an external circuit???