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AD6676 maximum input power (PIN_0dBFS and IDAC1FS) question

Category: Datasheet/Specs
Product Number: AD6676
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?

Parents
  • 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



Reply
  • 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



Children