DAC38J84: Calculation of noise floor

Nir Flysher

Expert 3367 points

Part Number: DAC38J84

Dear Team,

Can you please help with how to calculate the NSD in dBm/Hz of the DAC38J8x ?

The datasheet NSD is defined in dBFS/Hz and it is not clear what is the full scale power in dBm.

On one hand it is defined as 20mA on our tables but on figure 8 it implies it can reach 30mA.

Regards,

Nir.

over 5 years ago

0 dBrock over 5 years ago

TI__Genius 12780 points

Hi Nir,

We are taking a look into your question, and will be back with you soon.

Best Regards,

Dan

0 Kang Hsia over 5 years ago

TI__Guru* 78264 points

Nir,

With the default datasheet parameter based on 2:1 transformer, the output voltage delivered to the 50ohm load is 0.707Vpp

Current_Source_DAC_2_1_XFRM.TSC

you may use the TINA simulation above to figure out the output swing, and also the calculator tool below to figure out the equivalent output power

with the NSD in dBc/Hz, you can figure out the equivalent power for the noise.

0 Nir Flysher over 5 years ago in reply to Kang Hsia

TI__Expert 3367 points

Hi Kang,

Thanks for the detailed answer however it doesn't answer completely my original question.

If we increase the output current from 20mA to 30mA would we be able to gain on SNR (let's say that we can scarify some linearity performance for better SNR performance).

In other words, does the increase of the output current increase the noise floor as well ?

Can we achieve better NSD if we do this ?

Regards,

Nir.

0 Kang Hsia over 5 years ago in reply to Nir Flysher

TI__Guru* 78264 points

Hi Nir,

You should in theory achieve slightly better SNR (1 to 2dB per the plot below). The NSD (dBc/Hz) also scales close 1:1 with output current. Therefore, even though signal power is larger, the noise also grows at proportional rate

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DAC38J84: Calculation of noise floor