I have implemented the DC blocking capacitor as shown on a previous post to create the level shift at 2.7V.
I am seeing some ringing on the Vector Signal Analyzer on the burst power output. Attached are the pictures of the VSA output and the IQ waveforms into the modulator.
I realized that I probed the output of the DAC (AD9115) and did not show the output of the lvl shifted waveform. The waveform does not look good going into the ADRF6720-27.
I have ordered the ADRF6720 so that I don't have to have the level shift circuit. Looking at the datasheet for the ADRF6720 it shows a sample interface in Figure 45. It says to set the DAC to 10mA midscale current. I am using the pin mode configuration for the AD9115. Should I set the FSadj current value to full scale 20mA or 10mA? Is this level shift circuit with the DC blocking capacitor causing this ringing on the output that I am seeing?
It looks baseband inputs to ADRF6720-27 are the modulated signal. I suggest to check it with a CW single-tone (few MHz) and check four inputs at phase/amplitude.
what is CH3 on your screen shot? Is it enable signal to transmit signal?
Is ADRF6720-27 and level shifter all time on and just control baseband inputs on/off? I am not sure if we can see any abnormal operation (like ringing in 200us range) on spectrum analyzer but can you try to check output spectrum with spectrum analyzer?
I don't think DC blocking capacitor causes this ringing. Let's see how it looks like with a CW tone.
For ADRF6720 with AD9115 DAC,
Set full scale 20mA on AD9115 and 10mA midscale with set 500mV with 50 ohm termination on DAC.
CH3 is the ENBL on the IQ modulator.
I switched the IQ modulator to the ADRF6720 and everything seems to be working well. Thanks for the support.
It is good to hear ADRF6720 works.
FYI, If you consider ADRF6720-27, it can interface to AD9152/54 directly without a level shifter.