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LMV221

Lahiru Raffel
Prodigy 40 points
Other Parts Discussed in Thread: LMV221

We are using the LMV221 as a detector in the 130 - 180 MHz band and are seeing output noise in excess of 50 mV RMS when the specification is a maximum of 150 uV. The level of noise at the output varies with input RF frequency and temperature. Is there detailed information about output noise performance in 130 - 180 MHz band. Has the phenomenon of the output noise variation with frequency and temperature been observed. Are there any known batch issues related to output noise for this device. 

  • 0
    TI__Intellectual 1235 points

    Hello Lahiru Raffel

    Could you please provide more information on the conditions for which the noise issue was observed?

    Thanks,

    David

  • 0 in reply to David Diaz Quintana1
    Prodigy 40 points

    Hi David

    I have ordered an evaluation board for the part that should be arriving today. I will see if the noise is present on the evaluation board to try and determine if the noise is related to our layout. 

    In our application the noise is present under normal conditions. It is dependent on the RF frequency being input. We have checked for the noise from 100MHz to 1GHz. It is present from below 200 MHz occurring every 5 MHz. Above 200 MHz the noise reduces and by 350 MHz it has pretty much disappeared. The RF level into the RFIN of the device is -20 dBm. The noise is observed on the OUT pin of the device at 30 mVp-p. So for example on a particular device if we see the noise 150.85 MHz RF input we will then see it at RF input frequencies of 155.85 MHz, 160.85 MHz, 165.85 MHz etc

    Regards

    Lahiru Raffel

  • 0 in reply to Lahiru Raffel
    Prodigy 40 points

    Also this noise is not present on the device power supply line.

  • 0 in reply to Lahiru Raffel
    TI__Intellectual 1235 points

    Hello Lahiru Raffel,

    Thank you for your reply.

    Please, bear in mind that the noise measurements expectations according to the specifications should be based on how well your measurement conditions are aligned with the conditions provided on the data sheet. In this case, according to the specifications the maximum output noise of 150 uV (RMS) should be expected when the integration bandwidth is 1 KHz to 6.5 KHz. This point could be a potential source of discrepancy between your expectations and actual device performance. Is the expectation for the noise to be below 150 uV (RMS) for integration bandwidth 130 MHz to 180 MHz? Also, if you are using a modulated signal as opposed to a continuous wave, residual ripple could be observed at the output due to AM/Phase modulation.

    As you mentioned, it is probably a good idea to test the evaluation board at the specific conditions of your interest not only to understand the potential contribution of your layout from the output noise standpoint, but also to have an idea of the device performance when conditions others than the ones specified are used.

    Regards,

    David

  • 0 in reply to David Diaz Quintana1
    Prodigy 40 points

    Hi David

    The 1 kHz to 6.5 kHz is the noise bandwidth of the device output. The 130 MHz - 180 MHz is our operating range into the device RF input. 

    The link below shows a video demonstrating the noise.

    https://drive.google.com/file/d/0B0OnNkghfX7mRmhaZjVnNHBCMDQ/edit?usp=sharing

    Regards

    Lahiru

  • 0 in reply to Lahiru Raffel
    TI__Intellectual 1235 points

    Hello Lahiru,

    Thank you for the video.

    Based on the video it seems that the cable you are using it might be too long. As a consequence, the cable might be adding undesirable capacitive/resistive load which could affect negatively the device performance.

    I have a question regarding the cable connecting to the FFT analyzer. Based on the video it seems that the cable is directly connected to the FFT analyzer. Is this a 50ohm input? 

    Also, can you share what noise range would be appropriated for your application?

    Regards,

    David