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THS3091: 2nd Harmonic Distortion

Part Number: THS3091
Other Parts Discussed in Thread: THS3491

Hi,

Could you tell me what is the min/max value of the 2nd Harmonic Distortion at 1 MHz and Vo = 10 Vpp under the conditions in Fig. 13 of the data sheet?
As background, a customer measured under similar conditions and found that 2nd Harmonic Distortion = -62 dBc.
The data sheet says about -75 dBc, so I would like to know if -62 dBc is reasonable.

Best Regards,

Nishie

  • Hello Nishie, 

    There are many things that to into determining the HD2. -62dBc seems low vs typ -75dBc, but some small difference in the test setup might explain it - can you get the detailed set up and measurement approach - remember you have to filter the input very well to make this measurement. 

    Also, if he needs better, the THS3491 was intended as an upgrade to the THS3091

  • Hello Nishie,

    In addition to Michael's excellent reply, I wanted to share that for an AC performance spec like HD2, the performance can be correlated with quiescent current, Iq.  Iq is a spec tested on the device, which has min/max data points.

    I second Michael's statement and would also support the THS3491 as an option depending on your customer's need.  If you can share circuit & test setup details, we can best help address your question.

    Best,

    Alec

  • Yes, here is the THS3491 HD plot of interest, 

  • Hi Michael-san, Alec-san,

    Thank you for your reply.

    I will check the circuit configuration and measurement conditions with the customer.
    I would like you to check the schematics, etc., but is it possible to respond by private email?
    If possible, please give me your e-mail address.

    Also, is it possible to get the maximum/minimum data points of iq under the customer's measurement conditions (Vs = +/- 15 V, G = 5, f = 1 MHz, RL = 100 ohm, RF = 1 kohm)?

    Best Regards,

    Nishie

  • Hello Nishie-san,

    I will message you so you can email me directly.  I understand not all customers prefer to share their schematics or issues online.  I am checking with our design & validation teams about the possibility of your final question, or at least how to best help your customer.

    As we are discussing this thread offline via email, I am moving this post to resolved.

    Best,

    Alec

  • Hi Alec-san,

    I replied to your email regarding your question.
    Please also comment on the schematics and waveforms.

    Please move this post to resolved.

    Best Regards,

    Nishie

  • Hi Alec-san,

    I would appreciate it if you would update me on this matter.

    I look forward to hearing from you. 

    Best Regards,

    Nishie

  • Hi Nishie,

    can you explain how the customer has measured the second harmonic of 1MHz sine signal? I ask because measuring a so small distortion is not trivial (as already mentioned by Michael and Alec).

    Is the customer sure that the harmonic is not coming from the input signal itself? Is the customer able to generate a 1MHz sine with a total distortion under 80dB? What shows a distortion measurement of the input signal?

    It's important that the 1MHz sine input signal does not only show a very low distortion at the second harmonic but also at all higher harmonics. Otherwise unwanted intermodulation distortion can generate artefacts which appear looking like the second harmonic.

    A meaningful measurement can only be carried out by an (expensive) spectrum analyser in combination with a suited pre and post filtering. Again, measuring a so small distortion is not trivial at all.  

    Kai

  • Hi Kai-san,

    Thank you for your support.

    The customer is using a function generator to input 1MHz signals.

    The customer also did an ABA swap and confirmed the 2nd HD.
    This confirms that there is a performance difference between devices.

    I would like to extend the material I sent to Alec-san to you.
    Can I have your e-mail address?

    Best Regards,

    Nishie

  • Hello Nishie-san,

    I have sent a short reply to your email.  Please share any relevant information you are able to share on the forum; please also answer any questions you can from myself, Michael, or Kai on your measurement setup and broader distortion results.

    Best,

    Alec