Biasing HMC6505A using a HMC920

Hello,

We are trying to bias the HMC6505A eval board using the HMC920 full-featured eval board. HMC6505A operates at Vdrain of 5V and Vgate between -2 to 0V (tolerant up to -2.5V) to adjust Idrain to 120mA. Based on the information for HMC6505A we adjusted HMC920 full featured eval board R10 to 15 kΩ for Vdrain of 5V and R19 to 1105Ω Idrain to 120 mA. Also made sure SW2 EN, and SW1 VNEGFB, VGATEFB are left floating. After setting up everything we supplied 5V Vdd to the HMC920 eval board, we saw Vdarin as 5V, and VGATE as -2.5V, but the active bias control was not adjusting VGate to accommodate Idrain of 120mA. Is there something I am missing in setup to turn on the active bias control?

Thank you in advance!

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  • +1
    •  Analog Employees 
    on Dec 11, 2020 10:35 PM

    Hi Sanjmehta,

    Based on the datasheet it seems like the HMC920 can power the HMC6505A. The HMC920 only needs to drive the VDD2+VDD3 controlling Vgg1. The gain control needs to happen separately of the HMC920. Is this how you are trying to operate it? It sounds like you are configuring the HMC920 correctly from the information you've given me.

    Thanks,

    DanO

  • Hi Dan,

    Thank you for getting back to us. We were configuring it correctly. We figured out what was wrong, the bias controller input power supply was set at 5V but was only outputting 4.99V, and the Vdrain was set to 5V, so turning up the input power voltage slightly resolved the issue.

    Thank you,

    Sanj

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