CAC-1301 or CAC-1302 better for CRT monitor, which one has higher bandwith(Pixel clock)?

Updated on 14-01-2021 in Adapters and Cables
5 on 12-01-2021

“CAC-1301 • Triple 8-bit DAC (Digital-to-Analog Converter) with clock up to 210-MHz. • Integrated tripler 10-bit,162MHz video DAC for analog VGA signal output” Does this means it has pixel clock of 210 or 162Mhz only? Compared to “CAC-1302 Support HDMI™ resolutions up to 1080p@60HZ, HDMI™ Bandwidth 165MHZ/1.65Gbps per channel (4.95Gbps for all channels), which means only 165Mhz of pixel clock?

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4 on 13-01-2021

For the CAC 1301:

If 8bpc can do 210 MHz, then I would expect 10bpc to do 210*8/10 = 168 MHz but maybe there’s some overhead I don’t know about.

Those are the max pixel clocks – it should be able to support lower pixel clocks.

1920×1200 60Hz requires 154 MHz (using CVT-RB timing) or 193 MHz (using CVT or GTF timing which is probably what should be used for VGA displays or at least CRTs).

1080p 60Hz is 138 MHz (using CVT-RB) or 148.5 MHz (HDMI) or 173 MHz (using CVT or GTF).

The product page says “DisplayPort 1.1a  compliant receiver offering 5.4Gbps bandwidth over 2 lanes”. Why does it mention DisplayPort for a HDMI adapter? Maybe the DisplayPort part was not meant for this product since it’s not mentioned in the PDF specification sheet? The PDF specification sheet also does not mention the 10 bpc capability. Is the product page accurate? Maybe it should mention what chip it uses so we can look up more detailed/better written specs.

Two lanes of DisplayPort 1.1a can do up to 216 MHz at 8bpc and 173 MHz at 10bpc but there needs to be some room for overhead. 

HDMI 1.4 can do up to 340 MHz 8bpc or 272MHz 10bpc.


For the CAC-1302:

This adds analog audio input. It also adds HDCP support even though VGA displays don’t support HDCP?

“165MHZ/1.65Gbps per channel (4.95Gbps for all channels)” This means it’s using max speed of HDMI 1.0 or DVI. HDMI transmits 10 bits for each byte of data, so the amount of data is 3.96 Gbps total.

3.96 Gbps can do 165 MHz 8bpc or 132 MHz 10bpc.


VGA adapters in general:

I don’t see any reason to consider 10bpc for analog output. I’m not sure any DACs support 10bpc so you can probably ignore all the 10bpc numbers.

Even if a VGA adapter says 1080p or 1920×1200 is the max, that doesn’t mean that it cannot do more. For example the Plugable USB 3.1 Type-C to VGA Adapter says it supports up to 1920×1200 60Hz but I can get it to do 330 MHz (the adapter supports two lanes of DisplayPort 1.2 which can do up to 360 MHz 8bpc). I haven’t checked with an oscilloscope if the rise and fall time of the VGA output signal between a black and white pixel is less than the period of a single pixel but that’s not as important as the resolution and frame rate in most cases.

on 13-01-2021

Thank you so much for explanation! I guess in my case i will get 210Mhz which should be enough ony my hp d8911 with lower interlaced resolution and higher refresh rate and i know that type C offers cheap solution with high bandwith but rx580 and gtx1080 doesnt have those connections and i dont want DP to VGA, because i read it wont work with interlaced resolutions, so if this adapter can do 210 and my pixel clock calculations are right it should be more then enough for me, thanks again!

on 13-01-2021

Also whats the point of 1.4 adapter if it cant do 340mhz anyways, i guess its limited by VGA output.

on 13-01-2021

Good question. I looked at
I guess the point is that it doesn’t require HDMI 2.0 which many laptops/desktops don’t have. I don’t know of any laptop/desktop with HDMI that has a version that is not at least HDMI 1.4.

HDMI 1.0 was limited to 165 MHz.
HDMI 1.1 added DVD-Audio but I think the CAC-1302 uses LPCM audio.
HDMI 1.2 adds support for arbitrary resolutions and refresh rates – this is important for displays that don’t use the HDMI 1.0 modes.
HDMI 1.3 adds support for 340 MHz. This is important for higher resolutions and refresh rates.
HDMI 1.4 adds 4K but these club-3d adapters can’t do that. It also adds new color spaces and 3D which I don’t think are important for VGA output.

on 14-01-2021

I already ordered CAC-1301, because we dont have options for high end adapters here in Norway, really hoping that it can do 210mhz, thank you again!

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