Can I use ADG801to switch DC bias of Gain block?

Hi,

I am designing a RF transmitter/ receiver system. While in receive mode (which is default mode) all the RF devices (amplifiers) of the transmitter chain need to be in off state. They will be switched ON only when in transmit mode.

Generally I use MOSFET & BJT combination to switch the DC supply for RF devices (amplfiiers).

In case of gain amplifier (low RF power devices) I want to use ADG801 or similar device because this gain amplifier needs only 150mA (max) at 5.0V. ADG801 will help me in reducing the BOM as well as occupy less space & easy functioning.

Kindly give your suggestion on this approach.

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  • 0
    •  Analog Employees 
    on Jun 12, 2017 10:51 AM

    Hi Rajan,

    I think you should reach out the mini circuits as well on this but my feeling using the ADG801 should be ok in terms of current handling.  But at a minimum you will need to think about power supply sequencing and charge injection effects for the switch.  Notice in your schematic how you will be applying Vdd and Vs to the switch at the same time, this is not a good plan.  Power supply sequencing is important in all circuits (including how you power up the amp), you need to insure Vdd and ground are present before Vs otherwise you will forward bias the internal ESD diodes and latch up the part. See this app note and this app note for some background on this topic with respect to switches.  Charge injection when you switch the part is another item to consider. You will see a short duration output voltage spike when you toggle the switch, this could be outside the absolute max ratings for the amp bias voltage. Putting decoupling caps on the output of the switch can help.  See figure 8 in the ADG801 datasheet and this Q&A to learn more about charge injection. 

    Hope the above helps. 

    Regards,

    Eric.

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  • 0
    •  Analog Employees 
    on Jun 12, 2017 10:51 AM

    Hi Rajan,

    I think you should reach out the mini circuits as well on this but my feeling using the ADG801 should be ok in terms of current handling.  But at a minimum you will need to think about power supply sequencing and charge injection effects for the switch.  Notice in your schematic how you will be applying Vdd and Vs to the switch at the same time, this is not a good plan.  Power supply sequencing is important in all circuits (including how you power up the amp), you need to insure Vdd and ground are present before Vs otherwise you will forward bias the internal ESD diodes and latch up the part. See this app note and this app note for some background on this topic with respect to switches.  Charge injection when you switch the part is another item to consider. You will see a short duration output voltage spike when you toggle the switch, this could be outside the absolute max ratings for the amp bias voltage. Putting decoupling caps on the output of the switch can help.  See figure 8 in the ADG801 datasheet and this Q&A to learn more about charge injection. 

    Hope the above helps. 

    Regards,

    Eric.

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