Question about HMC7229

Hi Analog Device Team,

I bought the RF Power Amplifier HMC7229 and design a Roger 4003c PCB, after I have mounted the Chip on the PCB, together with the bypass capacitors, I measure the module with Network Analyzer, I could only get low gain of 12 dB instead of 24 dB and the Chip is very hot. I have tried many chip but it is still the same.

I use the Supply voltage as 5.3 V and gate voltage of -0.8 V to get 1.2 A. But the gain is low I do not know why.

But S11 and S22 can obtain < -10 dB

I have also designed the suggestion circuit in datasheet for Vref and Vdet, but it does not help.

Could the Team figure out my problem?

Thank you.

Regards,

James NG

  • Hi James,

    I would need more information about your design/application as you are getting half the expected gain and something is obviously wrong (especially if you saw this across multiple parts). If you provide more information about your design and exactly how you are integrating it/using it with the amp I can take a look. Unfortunately, I cannot determine your problem with the information provided.

    Thanks,

    DanO

  • Hi DanO

    I sincerely thank to your reply. Sorry for no providing info in last thread. Here is the module using HMC7229, I use the K connector as the connectors. I have used the 0402 100p, 0603 10nF and Tan Cap of 10uF (I cannot find 4.7uF in the electronic market of my city). 

     

    Here is the board layout, and I upload the whole board and zoom in view

       

    I have followed the datasheet to build this. Some pin are N/C, but I have checked the demo board schematics and found the it is connected to ground.

    As I need to build the module, so that I have designed the power management board also. Here is the schematic

    I used 4 Regulators to supply the VDD1, VDD2, VDD3 and VDD4. For the gate, I use the battery as negative supply (+ as ground and - as negative supply V-). I use LM324 to build suggested circuit in datasheet p.14 of 15, which is used to sense the Vref-Vdet. And another OP to drive the VGG1

    Here is the measurement result. I follow the bias sequence of the datasheet. Although the die is very hot during hte VGG=-0.8V, total current = 1.2 A, I can turn off the gate VGG=-2V. As a result, I don't think the chip is burnt right now.

    I am frustrated on the measurement result. Could anyone figure the problem? I

    Thank you for your help.

    Regards,

    James NG

  • Hi James,

    I do not see anything glaringly wrong with your schematic or set-up details. Your DC seems to be normal as it pertains to gate voltage to reach nominal IDD. Your output return loss is worse than expected which might be contributing to this but I wouldn't think the drop in gain would be this drastic. Can I ask if all of these parts have the same date code/lot number? I can investigate the lot and see if anything is strange or obvious as far as that. Also were these parts stored in the same container and came from the same source? I understand your frustration and will try to help if I can.

    Thanks,

    -DanO

  • Dear Dan02,

    Sorry to reply late. I want to share some information about the debug. Currently there are two direction.

    One is the cooling the Amplifier by using heat sink and thermal paste. It could improve a little, about 3 dB , but it still drop nearly 10-dB from the spec.

    The other issue is the material of PCB. I use the Rogers 4003C for design the microstrip line. The opeartion frequency is around the 38-GHz. But a senior PCB engineer has told me that Rogers 4003C is not suitable for this frequency. I think that it may be the main issue of gain-drop

    If you have any other insight on the issue. Please let me know.

    Regards,

    James NG