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AD9364 TX Power Monitor operation and duration calculation question

Category: Hardware

TX Mon operation (continuous mode):
Can you confirm that TX Mon operation in continuous mode is as follows:
- TX Mon delay counter starts after ENSM enters TX state (given that level threshold is either set to 0 or has been met)
- after TX Mon delay counter expires the measurement duration starts
- at the end of TX Mon duration the measurement is done and the TX RSSI register gets updated
- also at the end of TX Mon duration the TX Mon delay counter starts again
- after the TX Mon delay counter expires again the measurement duration starts again
- at the end of TX Mon duration the measurement is done again and the TX RSSI register gets updated again
- all of this keeps repeating until the ENSM exits the TX state

The specific fact I am looking to get confirmed is that each measurement period comes with another delay instead of having the delay just once at the beginning and then just periods of duration.

So it looks like this:
| delay | duration | delay | duration | delay | duration |...

And NOT like this:
| delay | duration | duration | duration |...

TX Mon duration calculation:
The TX Mon Duration (register 0x06E bits 3:0) calculation is given in the datasheet as:
Duration (Tx Sample Cycles) = 16 x 2^(value)

However, a test setup I have that allows me to see when the TX RSSI register updates suggests that this formula is not correct. When modifying the formula to:
Duration (Tx Sample Cycles) = 2^(value) [removing the factor of 16] it seems that the math matches what I am observing on my test setup much more closely.

Is there a chance that the formula in the datasheet is wrong either in the way I laid out or in some other way?

As for additional background: I need tight control as to over what part of the ENSM TX state the measurement is done. Ideally I would like to operate in single shot mode instead of continuous mode. However since this is not officially supported I need to fully understand how the timing in continuous mode works in order to set up the measurement correctly.

Thank you for your help with this.

  • When the ENSM enters the TX state, the Tx Mon Delay Counter starts. After this counter expires, the AD9361 measures Tx RSSI during the TX mon measurement duration. At the end of the TX monitor measurement duration, the TXRSSI value gets updated.

    And NOT like this:
    | delay | duration | duration | duration |...

    So the above is correct.

    In continuous mode AD9361 continuously measures TxRSSI until the ENSM exits the Tx state.  

    The TX RSSI measurement duration follows the equation(duration= 16 x 2^(value)) as mentioned in the regmap. Considering the above duration and delay slots, is the measurement values matching with your testings?

  • No, this is not matching my testing. I am constantly reading the RSSI register (approximately every 660 ns) so I can see when the register updates. From that testing I can see that:

    1. EACH update throughout one TX state of the ENSM happens later (not just the first one) when I adjust only the delay and not the duration. If what you are stating is true (that this: | delay | duration | duration | duration |... is how it works) I would expect only the first measurement to happen later and then the following ones would still just be spaced apart the same amount but this is not the case. Instead each update happens later when just changing the delay and that is why I am thinking it works like this: | delay | duration | delay | duration | delay | duration |... instead. Do you have a setup to test / verify this on your end?

    2. With the same setup I can see when I get RSSI register updates and the formula as stated in the datasheet does not match what I am measuring, instead it appears to be matching the formula when changing the 16 to a 1 in the formula. Again, is there a way for you to verify this?

    Thank you for your help with this issue.

  • we are looking into this and will reply back  soon.

  • Do you have an update on this?

    Thank you!

  • Analog Devices, can you please reply?

  • Are you testing using modulated or CW signal?

    Are you relying on change in RSSI power readback for measuring the TX monitor delay or power measurement duration? Can you please share the results of your testing?

  • I am using a modulated signal.

    I am relying on changes in the TX RSSI register in order to measure when an update happens (I can't specifically measure the delay or duration separately).
    The result of my testing is basically what I already mentioned but let me summarize the main facts:

    - with our default settings I get 9 updates during one single TX burst

    - varying the delay does NOT only change when the first update happens but also affects the following 8 updates -> this tells me that the delay is being used on every update and not only on the first one

    - the time when an update actually happens does not match the formula given in the datasheet (according to the datasheet our duration should be 170 us but instead it is 10.66 us)

    Would it be helpful to have a call about this? How else can I help you to help me figure this out?

    Since we can't use single shot mode as it is not supported I really need to find a solution to this issue so that I can make sure the RSSI gets measured at the right time during the TX burst in continuous mode.