Can I use ADG801to switch DC bias of Gain block?

Hi all,

Kindly reply to my query. I need to complete the circuit design.

Regards,

Rajan

Hi Rajan,

I think you should run this application past our amp group as well for feedback. what amp are you using?  The application here is you want to turn on/off the supply voltage to the amp?  You should also look at our load switch options that are specifically designed for switching in power supplies. 

Regards.

Eric.

Hi Eric,

This amplifier is a wideband PHEMT based MMIC amplifier with P1dB of 20dBm (0.1Watt) RF power (minicircuit MNA-6A+). Yes I want to turn on/off the supply voltage of amplifier.

Thanks for suggesting "Load switch" devices. It looks like load switch will be more suitable for this requirement as compared to Analog switch.

Thanks & regards,

Rajan

Hi Eric

I checked "load switch" devices. These devices are good covering voltage as well as current requirements.

But the turn-on / turn-off times are very high.

I need turn -on time less than 5us where as Turn-off time can be 100us (approx).

Considering Timing requirements can we select ADG801 for my application.

Regards,

Rajan

Hi Rajan,

Looking at the MNA-6A+ datasheet, the DC biasing conditions look different to what you are posing, they recommend a very specific setup using a 33ohms resistor on pin 8 and a 1000pF shunt cap connected to pin 7 and 8 which are shorted to the DC supply.  Your schematic looks different, you are biasing up on the output? Will this affect RF matching?  Have you been in contact with Minicircuits for support on using that product in the configuration you have?  I can't really comment on it.   

Note, we have a range of similar amplifiers that are supported.  The HMC375LP3 comes to mind, you can ask questions in the RF section in EZ on it.

Regards,

Eric.

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.

Hi Eric,

Thanks for the reply.

In the figure (in my very first post) , I have tried to describe my circuit using a generic RF amplifier block diagram. I have not inserted MNA-6A+ specific application circuit in this figure.

Yes there is a specific resistor requirement in case of MNA-6A+ device & we are designing RF card as per manufacturer's recommended application circuit.

HMC375 frequency of operation is not matching with our project's frequency band.

Still we have not finalized the DC on/off scheme for this RF amplifier due to long Turn ON  & Turn off Timings of Load switches. Plz check my last post for details.

Plz share suggestions on using ADG801 to turn on/off this amplifier.

Regards,

Rajan

Thanks eric.

I will take care of power sequencing & charge injection effects.

Regards,

Rajan

Hi Rajan,

Good. 

btw, the last link in my previous comment was incorrect.  Here is the correct Q&A link. 

Regards,

Eric.