sharkies
Member level 5
I'm at the final phase of the tape out. and I have some concerns with my DAC
I have a current-steering DAC with 500MHz clock rate. It is a 10-bit DAC with 2mA current. Cosidering output resistance of 50ohm, the LSB size is around 100uV.
Here's the problem, I connected my latch (the block that feeds digital signal to the switch transistor pairs in the current source) to the analog ground which the DAC ground is connected to. I used to have a separate digital ground, but now it is just combined to DAC ground for complicated layout reasons. When I do this, the DAC output signal has some distortion. When the signal is suppose to stay flat between to 2ns time period(since it is a 500MHz clock rate DAC) it has some fluctions in several mV range. This is well over LSB signal amplitude. I didn't have this when I used the separate digital ground for the latches. Do I have to be concerned of this? Or is this natural when desigining DACs? and will it be automatically taken care of by the following filtering stages. Please do let me know.
I have a current-steering DAC with 500MHz clock rate. It is a 10-bit DAC with 2mA current. Cosidering output resistance of 50ohm, the LSB size is around 100uV.
Here's the problem, I connected my latch (the block that feeds digital signal to the switch transistor pairs in the current source) to the analog ground which the DAC ground is connected to. I used to have a separate digital ground, but now it is just combined to DAC ground for complicated layout reasons. When I do this, the DAC output signal has some distortion. When the signal is suppose to stay flat between to 2ns time period(since it is a 500MHz clock rate DAC) it has some fluctions in several mV range. This is well over LSB signal amplitude. I didn't have this when I used the separate digital ground for the latches. Do I have to be concerned of this? Or is this natural when desigining DACs? and will it be automatically taken care of by the following filtering stages. Please do let me know.
