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AD9152 not producing slow square waves

Question asked by kenneth.witham on Apr 10, 2018

Hello,

 

So we are using the AD9125 on out own board and believe we have it hooked up pretty close to whow the EVAL kits are made. For our application we will need to generate quite slow square waves (>1us long pulses). Currently the output of the dac looks almost like there is a high-pass filter on the output. There is a positive voltage spike on the rising edge and a negative voltage spike on the falling edge but a 0 level signal in between. It currently takes about 200ns for the signal to hit 0 after each pulse. When I program the DAC in DC test mode I am unable to get straight DC signals out. I can get nice looking fast sine waves at full-scale but once I drive those down to below like 20 MHz they start looking really ugly (last half of positive and negative side look like a decaying capacitor).

 

I have disabled the PA protection, modulation, inv sinc, pfir, and digital gain. Interpolation is 4x. DC offset is 0. Any ideas what I am missing? Our analog out chain looks just like the circuit on the EVMsso I'm not really sure what is going wrong.

 

Thanks,

Ken

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