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Hi , I am using the HMC8205 for designing of 35 W wideband PA , What i observed is the Gate voltage (Vg)is varying from IC to IC., for first IC the Gate voltage to achieve the Idq of 1.3A is -2.4V ,whereas for 2nd one it is -2.1V , and this IC is ve

Category: Hardware
Product Number: HMC8205

Hi ,

I am using the HMC8205 for designing of 35 W  wideband PA ,

What i observed is the Gate voltage (Vg)is  varying from IC to IC.,   for first IC the Gate voltage to achieve the Idq of 1.3A is -2.4V ,whereas for  2nd one it is -2.1V , and this IC is very sensitive suddenly the O/p Power is dropping from 44dBm to 9dBm and Drain current from 2.3A to 450mA while tweaking the Gate voltage from -2.2V to -1.8V using Potentiometer  to achieve e the required o/p power of 45dBm o/p Power at 6GHz ,Can i consider whether the IC is damaged? and whether any possibility to send these ICs for replacement (or) checking ?, We procured these IC's in qty of 3 from Mouser 

Regards,

Praveen

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  • Hi Praveen453,

                            You shouldn't be adjusting the gate voltage to adjust the output power of the amplifier. You adjust Vgate to set the quiescent current of the amplifier to 1300 mA. Then adjust RF input power level to achieve 45 dBm output power.  See Figure 27, in the MC820BF10 data sheet.

    Yes, there part to part gate voltage variation.

    Have you fabricated your board with thermal considerations, do you have a heatsink for the board?

    If you feel the parts have been damaged, you need to deal directly with Mouser for replacement consideration.

    Regards,

    Jim B

  • Hi Jim, 

    Yes ,I have taken all precautions while doing system testing where the Amplifier  is in Mechanical enclosure along with other Driver and Predriver Modules fitted on Heat sink with cooling fans , the reason for adjusting Vg is at 6GHz , I  observed less drain current ( 2A) drawing when compared with other spot frequencies from 500 MHz to 5 GHz  and HMC 8205 is having sufficient I/p power of 24-26dBm as per calculations

    Can I know is it not advisable to adjust Vg while system is up for HMC8205? When I adjusted Vg from -2. 2V to -1.5V  the power dropped to 10dBm and drian current to 450mA which appeared for me the second drain is not drawing current

    Need to discuss with Mouser or local ADI about the part replacement as i have only 1 qty left

    Regards,    

    Praveen Badam

  • Hi Praveen,

                        Since the current dropped to 450 mA it sounds like the 2nd stage opened from EOS, (electrical over stress).

    The VGate should be adjusted once initially to set the desired bias current and not adjusted during operation.

    Regards,

    Jim B

  • Hi Jim,

    Replaced the non working IC with new one and achieved desired o/p Power of 45.8dBm except at 4GHz and 6GHz  where the Power o/p is 43.5dBm  

    I used HMC8205 in one of my design for Jammer application  , i used RT-duroid 4350(Er=3.66) with substrate height of 30mil   

    Can you suggest any improvement at 4GHz ? or is it device dependable ?  the Returnloss at 4GHz is less -7dB compared to other spot frequencies                                                          

    Regards,

    Praveen 

  • Hi Praveen,

                         The return loss could be caused by several things. Board design, part to part variation. Have you reviewed the EVB Gerber files?

    The VB substrate is 10 mils thick.

    https://www.analog.com/media/en/technical-documentation/evaluation-documentation/gerber-files/HMC8205BF10-gerber.zip

    Regards,

    Jim B

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