As we know, we need add Vgg firstly, but HMC598 has two Vgg: Vgg1 and Vgg2, so how we can adjust the voltage of Vgg1 and Vgg2 to get it works normal. Which Vgg can decide the current of Vdd?
I apologize for a rather lengthy answer but after discussing this with the designer to be sure that amplifier stability was o.k. I thought it worthwhile to provide some detail as our other multipliers are based on a similar topology.
Please reference the block diagram shown in the datasheet. Vgg1 is tied to the FET for the multiplier itself while Vgg2 controls the amplifier circuitry. You'll notice that while there is only one gate voltage for the amplifier section, there are (2) drain voltages (Vdd2 and Vdd3). This indicates that there are (2) FET devices simultaneously controlled by Vgg2. Also notice that per the Electrical Specifications table that Vgg1 is typically set to -1.25Vdc while Vgg2 is biased at -0.8Vdc with a +5dBm drive level. I recommend setting both gate voltages to -2.0Vdc to start with as this will insure that neither the multiplier nor the amplifier sections are able to draw current until we allow them to do so.
If you're not familiar with multipliers this may seem odd, but Vgg1 isn't directly setting current on a FET device, it's setting the level where the negative 1/2 cycle is clipped, therefore it should be set last. In fact, the multiplier block itself isn't drawing any current however once the amplifier chain is set it does impact the current that the amplifiers draw. That being said adjust Vgg2 until you get 150-160mA or so (will depend on your RF drive level) then set Vgg1 so that the output power and isolation are optimum for your application. If the drain current is still low you can adjust Vgg2 to a nominal 175mA and re-check that power and isolation are still acceptable/. During this final step you may find it necessary to switch back and forth between Vgg2 and Vgg1 until you have some confidence that the settings are producing the desired performance.
I recommend that you repeat this on several devices to be sure that the settings to achieve optimum performance (at room temperature) are well understood. Following this you should verify the performance over the expected operating temperature range taking into consideration any bias variation that may exist.
Once a nominal setting is well understood you could then use the HMC920 Active Bias Controller which includes a negative bias generator, to automatically provide the required bias sequencing.
Hope this helps,
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