Scope for testing TV, Monitor, & Projector properties

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ithilienranger
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Scope for testing TV, Monitor, & Projector properties

Post by ithilienranger » Thu Apr 11, 2019 3:56 am

I am wanting to do reviews of consumer display devices like monitors and projectors (maybe TVs too) with in-depth testing. A few of the tests I would like to do would require an oscilloscope with a light/photo sensor. I am not sure what bandwidth I need despite many hours of research. Would the bandwidth needed be based off the refresh rate of the display(i.e. 60hz)? I am concerned that I may be missing something that would increase the bandwidth need by a large factor. Two of the tests: pixel response time and input lag, would relate to the refresh rate. The other would be for checking whether PWM is used, and at what frequency, to adjust the display's brightness.

Here is my source for using an oscilloscope for doing these measurements:
http://www.tftcentral.co.uk/articles/response_time.htm

So, basically I would like to do similar testing to the above website. It seems to me that the 150MHz bandwidth on their scope is overkill, but I have no background in electrical engineering. Which Picoscope would you suggest? Thank you ahead of time for any advice!

Gerry
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Re: Scope for testing TV, Monitor, & Projector properties

Post by Gerry » Tue Apr 16, 2019 11:44 am

Hi ithilienranger,

I'm assuming that you're specifically targeting monitors and TVs for gaming and movies (as opposed to design, graphics and image manipulation) where response time is more important than colour accuracy and resolution. For currently widely available display technologies the fastest response time is from Twisted Nematic (TN) LCD displays. According to this source (https://www.techspot.com/article/1788-d ... -compared/) the fastest available model is responding at 2.6ms (your linked reference has the fastest at 5ms). The response time of 2.6ms corresponds to a bandwidth of only 134Hz, so you could build in a significant amount of future proofing of your testing capability (say, down to 1 millisecond response times), and still not get our slowest PicoScope (at 10Mhz) to break any sweat. The linked reference only discusses Response Time which is shorter than Input Lag, and if a 350Hz bandwidth (for 1ms Response Times) is shorter than what is required by the other 2 tests, then bandwidth is done and dusted.

At a 350Hz signal bandwidth a 10MHz PicoScope 2204A (see here: https://www.picotech.com/oscilloscope/2 ... 0-overview) would give you more than enough samples (8k samples) to capture more than one waveform period from cycling pixels on and off. However you may need more buffer memory in the Scope for the other tests (without knowing the details of the tests I can't comment). Also, you would may want to just confirm that, for the measurements, 8-bit resolution of the PicoScope 2204A is enough.

Regards,

Gerry
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ithilienranger
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Re: Scope for testing TV, Monitor, & Projector properties

Post by ithilienranger » Tue Apr 16, 2019 3:11 pm

Yes, my testing will be focused around gaming and movies. Looking at others reviews that check for PWM use, the PWM frequency tends to max out around 1000hz. The fastest display I would test would be DLP projectors, with response times near 1 microseconds.

DLP Response Time Source (see Micromirror crossover time):
http://www.ti.com/lit/ds/symlink/dlp470tp.pdf

A scope with a higher vertical resolution is out of my budget. I think 8-bit is enough resolution anyways so long as I can zoom in on the waves. Am I correct in understanding that I could filter down to just the wave I am studying and regain waveform resolution? I am not sure on my buffer memory needs. PWM testing would just need to run the length of a frame. Reponse time is as you told me already. The input lag test doesn't need much bandwith but may need to run a full second.

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