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Control of external GaAs switches with ADAR1000

Thread Summary

The user is considering using an external GaAs switch with the ADAR1000 to control the signal path between PA and ANT or ANT and LNA. The ADAR1000 can provide the required complementary voltages (0.5V and -5V) through TR_SW_POS and TR_SW_NEG pins, which are mutually exclusive but can be controlled simultaneously via Register 0x31. The user also proposes using the TR_POL pin to achieve the other required voltage, noting a slight performance degradation when lowering the drive voltage from 0.5V to 0V, which is acceptable for their application.
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Category: Hardware
Product Number: ADAR1000

I'm considering to the use an external GaAs switch along with the ADAR1000 in order to have an external LNA and a PA. GaAs switches require two complementary voltages to control the signal path (PA to ANT or ANT to LNA). In my case, to set the TX path I need to set VA=0.5V and VB = -5V and to switch the RX path I need to reverse the voltages, i.e. VA=-5V and VB = 0.5V.

After carefully reading the ADAR1000 datasheet (page 38), I found that it provides two pins for driving an external GaAs switch:

TR_SW_POS = {0, 3.3} V

TR_SW_NEG = {-5, 0} V

TR_SW_POS and TR_SW_NEG are mutually exclusive (datasheet, page 42) so I can't have two wires, one with Vhigh and the other with Vlow, at the same time:

Can the ADAR1000 provide two simultaneous voltages as I mentioned above to drive a GaAs switch? If so, do you have an application example for the ADAR1000 with an external GaAs switch?

Edit Notes

Trying to make the explanation a bit clearer...
[edited by: andresmmera at 12:52 PM (GMT -4) on 29 Jun 2023]
  • The ADAR100 TR_SW pins were not intended to drive GaAs switches, but rather drive silicon switches like the ADRF5024 or ADRF5026.  These switches only need a single control voltage.  The examples given would use the TR_SW_POS pin.

    Would a slicon switch have high enough linearity and compression to meet you application needs?  The switches listed as examples are operational through 44 GHz.

  • Yes, ADRF5026 is very well suited to our application, but we prefer to use a GaAs device we already have.

    We only have one polarization. As a workaround, I think I can get the other voltage signal we need from TR_POL [-5, 0] V. Then, I would just have to change the POL bit with SW_DRV_TR_STATE. Is there a problem with this?

    There is a slight degradation on the switch performance for lowering the drive voltage from 0.5V to 0V, but it's not so critical for our application.

  • Logic wise I think this would work and you control both pins in Register 0x31, so they should change at the same time. 

    Do know both pins have 1mA of available push/pull current.