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# AD9371 External Signal Levels vs Internal dBFS

With a CW Rx Input at the AD9371 Maximum Recommended Input Power of -14 dBm and no internal Rx attenuation (Gain Table Index = 255) what is the expected digital signal power in dBFS?

Are these calculations correct?

-14 dBm : External CW Input

+18 dB    : AD9371 Rx Fixed Internal Gain

-7 dB       : ADC dBm to dBFS (Full scale ADC input is +7 dBm)

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-3 dBFS   : expected digital signal power

Also, what is the expected Tx Output power of a 0 dBFS CW tone with no internal Tx attenuation?

thanks.

• -3 dBFS   : expected digital signal power  Correct

Also, what is the expected Tx Output power of a 0 dBFS CW tone with no internal Tx attenuation? The Tx output power is 7dBm with 0dBFs input tone . Refer to the Tx output power vs attenuation graphs from datasheet for details.

• As per Ug992,

The full-scale input of the ORx path is −13 dBm (with a 0 dB
attenuation setting) for a single-tone input.

The full-scale voltage of the Rx/ORx ADC is 707 mV peak.

Both these statements are from ug992.  707mV peak correspond to 7dBm output. In ORx path, 0dBFS correspond to  7 dBm only.  Please confirm.

Also can you please point out where is it mentioned about "+18 dB    : AD9371 Rx Fixed Internal Gain" in ug992. is there any such fixed gain in ORX path. how do you map ORx input power to digital dBFS?

Thanks

• ORx Receiver has a gain of 18dB before the ADC. So ADC full scale and Max input both are correct.

-13 dBm is the recommended max input to Orx port.

Note from Datasheet FYR.

8 Note that the input signal power limit does not correspond to 0 dBFS at the digital output because of the nature of the continuous time Σ-Δ ADCs. Unlike the hard
clipping characteristic of pipeline ADCs, these converters exhibit a soft overload behavior when the input approaches the maximum level.

In u992, it's mentioned as full scale input of the orx path is -13dBm. Instead of mentioning as max input power, so that's y it was a bit confusing.

So does it mean max input power of -13dBm at Orx input corresponds to -2dBFS (-13+18-7).  Is this calculation correct for mapping input power to digital dBFS??

Can you please let me know where is it mentioned about the gain of 18dB before ADC?

Thanks

• So does it mean max input power of -13dBm at Orx input corresponds to -2dBFS (-13+18-7).  Is this calculation correct for mapping input power to digital dBFS??

Yes correct.

From Datasheet.

• Hi  ,

Thanks for the clarification

ADC resolution : 14 bit. Whatever dBFS we are calculating is it at the ADC output or in baseband JESD output ( After ADC we have a digital gain/attenuation block and in JESD interface 16 bits sample resolution)

In none of the default rx gain table values, why is digital gain/attenuator block never set in gain mode? Any specific reason.

Thanks