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# AD6676 maximum input power (PIN_0dBFS and IDAC1FS) question

Category: Datasheet/Specs
Software Version: datasheet Rev.D

In page 28 of datasheet, in the 'Maximum input power (PIN_0dBFS and IDAC1FS) ' section, it shows that a differential voltage swing of ±240mV peak is obtained for IDAC1FS equals 4mA. This where I feel puzzled. The reason is as following:

first, Rin=60Ω.

second, IDAC1FS=4mA.

thus, we analysis the input stage of AD6676 in the single ended, the single ended input resistance is RIn_single=30Ω,

since IDAC1FS=4mA, current swing provided by IDAC1 is ±2mA peak .

so, single-ended voltage swing of ±2mA × 30Ω=±60mV peak is obtained for IDAC1FS equals 4mA.

i.e. a differential voltage swing of ±120mV peak is obtained for IDAC1FS equals 4mA.

Why my result is different from the datasheet? Where is wrong?

## Top Replies

Mar 23, 2023 +1 verified

Hello,

Perhaps the best way to analyze is that IDAC1 produces  +/-4 mA AC current when DAC code is at max positive and negative settings,  This max AC current occurs when differential input of device is swinging…

Parents
on Mar 23, 2023 10:01 AM

Hello,

Perhaps the best way to analyze is that IDAC1 produces  +/-4 mA AC current when DAC code is at max positive and negative settings,  This max AC current occurs when differential input of device is swinging +/-240 mV.  If one models the DAC output as shown below........it would consist of two DC current sources of 4 mA and a "code-dependent" differential current source of +/4 mA.   Seems like the IDAC1FS refers to one leg of the differential DAC.

All that said..............an input in th range of -2 to -3 dBm (IF dependent) results in ADC full-scale  (PIN_0dBFS).

Regards