Re: MMIC question


Andy G4JNT
 

Yes.  The biassing is such that it is designed to be fed via a resistive droppery.  Internally biassing uses feedback to define a roughly constant voltage on the supply pin, which in conjunction with the reisstor causes the device to draw teh correct current.     If you 'force' the supply pin to a voltage above that it wants, excessive and uncontrolled current draw will result.   

Think 'Zener diode' - its a bit like one of those.

MMICs work best at a constant current defined externally, by an active current source.  That is te honly realistic way to run them correctly from a supply that isn't regulated.  There is no way you can correctly operate a resistively biassed device from a voltage equal to or below the specified value

HOWEVER, some device around do run from a constant voltage, and the data sheet clearly shows how these can be supplied via only a choke

'jnt


On 7 August 2016 at 08:40, richard@... [ukmicrowaves] <ukmicrowaves@...> wrote:
 

Hi all


I am working on a USB powered device that includes an MMIC. The MMIC runs on 5 Volts (at the chip) but the spec sheet describes it as a 6-12 Volt device and gives suitable dropper resistor values. The supply is properly decoupled and fed to the device by the normal RF choke (all to the datasheet's recommendations).Is there any problem that I might encounter running an MMIC direct from the USB supply?


73 Richard G3CWI


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