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AN-1363 and HMC980

Question asked by mantow on Jun 13, 2017
Latest reply on Jul 5, 2017 by kkaya

Hi Engineerzone

 

I'm considering to use the HMC980 for biasing the HMC1082, per Fig. 27 of the AN-1363 application note.

 

I'd like to better understand the role of R5 and R7. Though the recommended values are very large (1.6M), Table 2 and Fig. 3a of the HMC980 datasheet tell us to float the VNEGFB and VGATEFB pins.

 

In AN-1363, R5 and R7 are said to ensure VGATE is within the AMR of the HMC980, but the referred section on "adjusting the Default VNEG and VGATE thresholds" seems to apply to the DUT (i.e. the amplifier), no?

 

Please can someone explain the apparent discrepancies above ?

 

Many thanks in advance.

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