TLV3604EVM: Analogue to LVCMOS25/SGMII

Hi Shaun,

Since this is a question about the comparator's capability to interface with LVCMOS25 and SGMII devices, I will hand this post over to the Clocks and Timing group to see if they can provide further support for you. If you have questions about the TLV3604 itself then the Clocks and Timing group can reassign this post to the comparators group.

Kind Regards,

Joe

Thanks Joe

Hi Shaun,

It appears that TLV3604 can indeed accept rail to rail inputs. I reassigned this post to the comparators forum.

Kind regards,
Lane

Hi Shaun,

The TLV3604 can accept rail to rail inputs as specified in the datasheet. I understand that wasn't you question.

From what I can gather, you want an EVM that is ready to go for LVCMOS25/SGMII outputs. I will reach out to the rest of the comparators group to confirm that we do not have an comparator and EVM 'ready to go' for this type of output. I think you will most likely have to configure the outputs via external components yourself.

I will try to get back to you by end of business Monday (2/1).

Kind Regards,

Joe

Hi Shaun,

I would like to know more about you input high and low levels as well as your reference level.

Also what are your desired output levels? From what I can tell your desired input and output levels are described in figure 2 below from this document.

I know you mentioned 750mV high and 0mV low on the input so which levels are you using in your design?

As far as I know, we currently do not have any propagation delay output devices faster than 5ns (TLV350x).

Kind Regards,

Joe

Hi Joe,

So at this point my understanding is the reference level is gnd. There will be an analogue ook 1 Gbit signal with vil approx.  0V and vih approx. 250 mV, However, if this isn't suitable for a comparator input it could be amplified.

Ideally looking to go from analogue directly to LVCMOS25 with a development board as this is a table top system but could go analogue to any logic level that could be used with a translator dev board to then go to LVCMOS25. The LVCMOS25 levels I found are shown in the table below:

Cheers,

Shaun

Hi Shaun,

Thanks for that clarification.

As far as the input, I would recommend having a reference voltage in the middle of your input voltage range as opposed to 0V (maybe 150mV).

A 0V reference might cause unexpected transitions in the output.

For the output, the LVDS configuration of the TLV3604 cannot be used because the output common mode voltage of 1.2V and a 350mV swing each way would only produce levels at 850mV and 1.55V.

This mode is commonly used for the sake of speed because of the lower voltage swings.

Unfortunately, we don't have a device that has output levels 0.4V from either rail.

In a couple of months we will be releasing a comparator with a max toggle rate around 300 MHz. If you decide to use this device in the future, you can use schottky diodes connected to each supply of the comparator. Just ensure the supply current is high enough so that voltages are biased to the correct levels. This way, the output never exceeds VCCO - 300mV, and never goes below ~300mV above GND. I have attached a simple drawing of what I am trying to explain below.

If you can't wait for this device to release, or the toggle rate is not fast enough, I can forward this thread to the clocks and buffering team to see if they can find a high speed buffer for your application. I also assume that they could use the same schottky diode setup for the supplies.

I hope this helps and kind regards,

Joe

Hi Joe,

Thanks for your help,

Do we supply a reference voltage to the comparator, as well as the input voltage? I'll have a read and see if I can understand how these work better, I'm coming from optics and new to the electronics side of this.

I've asked about using different I/O standards to LVCMOS25 and will have a read on this too, so might be happy with LVDS.

I'm looking for something to get a system running soon. So maybe the part that is coming available is the longer term solution but in the meantime could you forward this thread to the clocks and buffering team to see if they might be able to help?

Once again, thanks for your help Joe.

Cheers,

Shaun

Hi Shaun,

Typically, a reference voltage is also supplied.

I will go ahead and forward this post to the clocks and buffering group to see if they can provide a buffer that fits your needs.

Kind Regards,

Joe