ADL5391 - Single Ended Input.

Hi,

I recently bought an evaluation board of ADL5391.

I intend to use it as an ASK modulator, but my input signals are single ended.

XP => Low freq. ASK

YP => RF Carrier

The low freq. ASK signal has 400mVpp (0-400m), so in order to have at the output the desired signal, I must implement a configuration as described in Fig.19 of the datasheet. However, I am having a bit of trouble in getting the right resistor values.

Can anyone help me?

Thank you and regards,

scpires

  • 0
    •  Analog Employees 
    on Jul 6, 2012 8:36 PM

    Hi Scpires,

    The evaluation board is setup to run single ended at the card edge via the baluns that are on the board.  You can access these via XP, YP and ZP for the inputs and WP for the output.  Please see Figure 23.

    What is the frequency range of your low frequency ASK signal?  Are you worried that it is lower in frequency than the low freq. corner of the baluns?

    Regards,

    Joel

  • Hi Joel,

    thank you for your answer.

    In fact, I use the simplest form of ASK, the OOK. So at the XP I have a square wave with fundamental frequency from 5 MHz up to 40 or 50 MHz and with duty-cycle variable. At YP I have an sinusoidal wave with 500 MHz of frequency.

    I've tested the board as it is described in Figure 23, but it did not work as I was expecting. Somehow the levels at the output remain the same (flat RFCarrier as it was in YP) with the 0-400mV that I have in XP. Then I made a test with a 5MHz square wave and when I increased the amplitude value (2.3V) the output started to behave as a PSK. So I was expecting that a single ended configuration would work. I assembled the circuit as in Figure 19, but only for XM and XP and I repeated the test with the 5MHz square wave at XP. Now the output is OOK but only if I put 2.3 V at XP. Is there a way to put it working with 400mV at XP by rearranging the resistor configurations?

    Thank you,

    Sergio

  • 0
    •  Analog Employees 
    on Jul 10, 2012 4:56 AM

    Hi Sergio,

    Do you have coupling caps on the inputs?

    There's a 2.5V common-mode and if you are DC coupled, you need to use 2.5 V as your reference (instead of 0V).

    There should not be any reason that the baluns couldn't work with a 5 MHz to 50 MHz square wave.  It should work single ended as well; the resistors in figure 19 should work as well.

    Thanks,

    Joel

  • Hi Joel,

    no, I removed the input cap of XP input.

    I've seen the 2.5V reference in the datasheet, so I figured that the resistors in figure 19 should work. And they do work, but only if I put a square wave with levels 0-2.3V at the input. However, I would like to have it working with levels 0-400mV.

    My question is, is there any resistor combination (figure 19) that allow it?

    Thank you for your time,

    Sergio

  • 0
    •  Analog Employees 
    on Jul 10, 2012 10:39 PM

    Hi Sergio,

    The resistors in Figure 19 don't reference the network back to ground, but rather they are matching resistors.  They were not designed to be DC level shifters.

    If you want to drive the device directly you have a couple of options.  You could put the coupling caps back on the inputs.  This should allow for 0 to 400 mV levels.  If you don't want to put on the coupling caps, then you must swing the signal, above and below 2.5 V.  You have to think differentially.  If Xp is at 2.9 V, and Xn is at 2.5 V, that is a differential voltage of +400 mV.  If Xp is at 2.1 V and Xn is still at 2.5 V, then the differential voltage is -400 mV.

    Best Regards,

    Joel