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RI-SMD-MRD2: VSP affect on transmit power

Nick Gilling1
Prodigy 60 points
Part Number: RI-SMD-MRD2

Hi there,

I'm wondering how changing the VSP supply affects the transmitting power, if at all? Currently have VSP/VSL tied to 5V and wondering if changing to 3V3 would affect this or not. There doesn't seem to be much in the reference guide regarding this. If I've missed something, please point me in the right direction.

Thank you!

Nick Gilling

  • 0
    TI__Mastermind 18265 points

    Hello Nick,

    when changing the supply voltage this will effect the output power. The supply voltage VSP is connected directly to a MOSFET half-bridge which drives the antenna output. Please note, both supplies (VSP/VSP) must have the same voltage (2.7V to 5.5V).

    Regards,

    Helfried 

  • 0 in reply to Helfried Vollbrecht
    Prodigy 60 points

    Hi Helfried,

    Thanks for the quick response. Do you know how much the output power is reduced? If we reduce VSP/VSL from 5V to 3.3V, would this mean our RF power would reduce by (3.3/5)^2 = 0.43? 

    If the power is reduced, is there a way in antenna design that we could compensate (i.e. increase turns)?

    Thank you!

  • 0 in reply to Nick Gilling1
    TI__Mastermind 18265 points

    Hello Nick

    I did a check with the Microreader EVM and measured the field-strength at 5cm distance

    5V -> 146.5 dBµA/m

    3.3V -> 141.2 dBµA/m

    with a 32mm glass transponder the read range changed:

    5V -> 12.5cm

    3.3V -> 10.7cm

    You should not change the number of windings of the antenna because this will change the resonance frequency. Depending on your application and space requirements you can use a ferrite antenna.

    Last thing that comes in my mind is the use of a DC/DC converter to come back to the 5V but this can, in dependence of the switching frequency, disturb the receive signal.

    Regards,

    Helfried

  • 0 in reply to Helfried Vollbrecht
    Prodigy 60 points

    Hi Helfried,

    Thank you very much for checking this. Is there any way you could perform the same experiment while supply the microreader with 3V? We are using a 3V battery for the application so wondering if we can just use that along with some power control switch. I believe our desired target range is 5cm so I would guess we are OK but if you could check that would be much appreciated.

    Thank you!

    Nick

  • 0 in reply to Nick Gilling1
    TI__Mastermind 18265 points

    Hello Nick,

    sorry for the late answer but I was not in the office the last week.

    At the moment I have not the time to check that again, but 3V or 3.3V should make a big difference. Because the read range depends from your antenna and the transponder used, it would be best to check the read range with your environment to get a reliable result.

    Regards,

    Helfried