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LMK04610EVM: Adjusting Output Amplitude

Leonardo Martinez
Prodigy 40 points
Part Number: LMK04610EVM
Other Parts Discussed in Thread: LMK04610

Tool/software:

Hello team,

I have run into a problem where I am trying to adjust the output amplitude of my output. I am trying to get the level up to at least 1 V (maximum) at 500 MHz. The problem appears when I decrease the divider of my output channels my amplitude decreases. So my question is, how can I adjust the settings in TICS Pro in order to have control over the output amplitude?

Thank you.

  • 0
    TI__Mastermind 33970 points

    sWhat's the bandwidth of the measurement instrument you're using to check the amplitude? If you want an accurate waveform amplitude, you probably want at least a factor of five higher analog bandwidth at the scope.

    The outputs page offers several controls for output drive mode and drive slew rate. Check that the selected drive mode generates the required swing in the first place - HSDS 8mA into 100Ω differential load produces a total swing of ±800mV from P to N, for instance. Additionally, the slew rate may need to be set to its highest setting for longer cables.

    On the outputs page, there is a table of all the output settings for very output at the bottom of the content area in TICS Pro. You can use this to select the drive mode and slew rate of individual outputs. You can also use the channel combobox at the top of the page and the "Apply to selected channel" masks to copy values from one channel to another, though be warned that it copies ALL values.

  • 0 in reply to Derek Payne
    Prodigy 40 points

    Thank you for your response Derek, the bandwidth limit of my instrument is 4 GHz. 

  • 0 in reply to Leonardo Martinez
    Prodigy 40 points

    I did as you recommended and modified the drive mode (set it to HSDS 8mA) and the drive slew rate (set to strongest). The amplitude control works when outputting low frequencies, but when my output frequency is 500 MHz or higher the range goes from 0 V to 200 mV. Now I am wondering if there is more setup required in order to have my desired amplitude at high frequencies.

  • 0 in reply to Leonardo Martinez
    Prodigy 40 points

    I did some setup changes where instead of using my oscilloscope probes I am now using some coax cables and it seems that now I have better control over the amplitude. I was expecting to obtain around 800 mV maximum but my results showed a peak voltage output of about 460 mV having Drive Mode: HSDS 8mA and Drive Slew Rate: strongest.

  • +1 in reply to Leonardo Martinez
    TI__Mastermind 33970 points

    I took a measurement on our 8GHz scope with an LMK04610 EVM, AC-coupled, 8mA HSDS and Strong slew rate, into 50Ω load. I've used known good SMA cables. The configuration used is the default configuration in TICS Pro (from the default configuration menu) but with the divider on the measured channel reduced from 8 to 2 to approximate 500MHz (we get 491.52MHz). I see around 750mV nominal drive strength.

    I suspect there is a setup issue somewhere in your system that is limiting the expected response, perhaps because of old/bad/unusually-long cables or poor contact with the measurement location. It's of course possible that something about the channel outputs is misconfigured, and I'd be happy to take a look at a TCS file or hex register dump to try to identify any misconfigurations. But given the large magnitude of variance seen with the probe vs the coax, I suspect setup issue more strongly than register issue.

  • 0 in reply to Derek Payne
    Prodigy 40 points

    Hey Derek,

    You are correct the length of the wires appeared to be the problem, under default configurations I measured the amplitude of 1 output (491.52 MHz) using different length coax cables and it seems that depending on length the amplitude will be altered. I am guessing that these wires are altering the impedance resulting in a change in amplitude. So my fix was just to get short and good condition coax cables.

    Thank you so much for all your help. Hope you have a wonderful day.