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Questions about HMC943APM5E Gate Current (Ig) and Biasing Circuit Design

Category: Hardware
Product Number: HMC943APM5E

Hello,

I’m currently designing a biasing circuit for the HMC943APM5E and have a couple of questions regarding gate current (Ig), which I couldn’t find specified in the datasheet.

  1. Gate Current Information Missing?
    The datasheet doesn’t specify the gate current (Ig), which is typically necessary for properly designing a bias circuit. My current biasing circuit is capable of handling up to 300 mA for Gate current Ig.

  • Is this sufficient?

  • Does the absence of Ig in the datasheet imply that it is negligible or doesn't matter ?

  • Am I misunderstanding something in terms of how Ig should factor into the design for this device?

  1. Gate Current Control Without Performance Impact
    Assuming Ig is non-negligible, is there a recommended method to limit or control gate current without degrading the amplifier's performance? For example, would using a series resistor or current limiter on the gate line negatively impact stability or linearity?

I’d appreciate any clarification or design recommendations based on experience with this part.

  • The gate voltage is being applied to the gate of a FET so it is very small under normal circumstances, typically much less than 1mA. In the next post, I'll attached a plot showing a power sweep at 30 GHz that includes the gate current. You will notice that the gate current only starts to increase when the output power is deep into compression. And then, it's just a few mA. 

    Note however that the gate current is negagive, that is, the current flows out of the Vgate pin.  So the source that provides the gate voltage must be able to sink current. 

    There is no need for protection circuitry. I would not add a resistor. As you get nearer to RF power compression, the current in the gate pin increases (more negative). If the gate voltage (on the other side of the resistor) is fixed, the increasing current through the resistor will make the gate voltage at the pin more positive which will actually increase (more postive) the gate voltage at the pin which could start a runaway scenario. - Eamon

  • XLSX

    HMC943APM5E Power sweep at 30 GHz that includes gate current. 

  • Many Analog Devices power amplifiers require a negative gate voltage for proper biasing (e.g., -0.85 V Vg in the case of the HMC943APM5E), and I’ve noticed this is common across several models. I’m currently struggling to find a convenient and reliable biasing circuit that can provide a stable negative Vg and also sink gate current when needed.

    Could you share a recommended or typical biasing circuit for this situation