Why lower resolution have higher refreshrate on lcd monitor?
Why lower resolution have higher refreshrate on lcd monitor?
I'm just curious about it. Almost every LCD monitor supports 75hz on 800x600 or 1024x768 or even 1280x1024, but when it comes to 1920x1080 it's always only 60hz [we don't talk now about high speed displays]. I always though that pixel clock is the wall, but then every lower resolution should have more and more hz till the maximum refresh rate [that we have in specification of monitor, almost every panel have something like 75hz], becuase the only limiation would be the maximum pixel clock that we have in our monitor [1080p60hz ~148.50mhz]. But in most cases it's not. Some monitors can display only 800x600@75hz and some go even to 1280x1024@75hz when both of them have maximum 1080p60hz. What's the case here? Is there some hardware thing that i don't know about or is it just software lock on display that deny every not predefined resolution even if it's not overclock?
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RLBURNSIDE
- Posts: 104
- Joined: 06 Apr 2015, 16:09
Re: Why lower resolution have higher refreshrate on lcd moni
They're not limiting your refresh rate to be mean if that's what you're asking.
Lower resolution = lower bandwidth = faster refresh.
If you want higher refresh at the same resolution, you need higher bandwidth. Given that all devices have a fixed maximum bandwidth depending on the clockrate and signaling capabilities (amongst other things), you can imagine that these LCDs were designed to allow 1080p / 60hz. Lowering the resolution from there allows you to reach higher refresh rates.
It's pretty simple. Bandwidth has a fixed maximum value on any device, most HDMI chips have been clocked at 165Mhz, which allowed 1080p / RGB / 60hz. You can calculate it yourself. You need about 120mhz of bandwidth for the pixels themselves, plus overhead.
Lower resolution = lower bandwidth = faster refresh.
If you want higher refresh at the same resolution, you need higher bandwidth. Given that all devices have a fixed maximum bandwidth depending on the clockrate and signaling capabilities (amongst other things), you can imagine that these LCDs were designed to allow 1080p / 60hz. Lowering the resolution from there allows you to reach higher refresh rates.
It's pretty simple. Bandwidth has a fixed maximum value on any device, most HDMI chips have been clocked at 165Mhz, which allowed 1080p / RGB / 60hz. You can calculate it yourself. You need about 120mhz of bandwidth for the pixels themselves, plus overhead.
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Falkentyne
- Posts: 2795
- Joined: 26 Mar 2014, 07:23
Re: Why lower resolution have higher refreshrate on lcd moni
He's right.
It's bandwidth that LCD's are concerned with. Pixel clock is only part of it. (you can exceed the bandwidth even at a normal resolution by increasing the "horizontal total" which self increases the pixel clock along with it).
CRT's were limited by their *horizontal scan frequency*. You could get the maximum vertical frequency (hz) (usually also with a known max resolution) by having the scan frequency line up, which could be calculated. A monitor with a Hor. scan frequency max of 127 kHz could run 1600x1200@100hz (this is exactly 127 kHz).
Of course the resolution could go higher but the refresh rate max keeps going lower. Pretty sure the maximum was 2048x1536@75hz (78hz if you were tweaking the timings). Sure enough that's 120 kHz, just in spec range.
It's bandwidth that LCD's are concerned with. Pixel clock is only part of it. (you can exceed the bandwidth even at a normal resolution by increasing the "horizontal total" which self increases the pixel clock along with it).
CRT's were limited by their *horizontal scan frequency*. You could get the maximum vertical frequency (hz) (usually also with a known max resolution) by having the scan frequency line up, which could be calculated. A monitor with a Hor. scan frequency max of 127 kHz could run 1600x1200@100hz (this is exactly 127 kHz).
Of course the resolution could go higher but the refresh rate max keeps going lower. Pretty sure the maximum was 2048x1536@75hz (78hz if you were tweaking the timings). Sure enough that's 120 kHz, just in spec range.