AM26C31: AM26C31 max signaling rate

Hi Jenny,

This device is RS-422 which traditionally doesn't support > 10Mbps ; that is where I think the 10Mbps signal comes from. 

However the datasheet doesn't say because the max speed is generally derived from the rise/fall time of the differential driver as well as the propagation delays of transmitter and receiver. 

This device has a max differential transition time of 10ns; we want the bit  to be at its max value for at least 1/3rd of the bit time - so using the max transition time spec we get a max data rate of:

Max_data_rate ~ 1/(3*max differential transition time); which in this case is 1/30ns = 33.3Mbps 

Now you also need to consider the propagation times of transmitter (which is most 12ns) and the receiver (I am not sure what receiver you are using - but that could impact max speed) - since you need 20Mbps that means the total propagation delay from receiver and transmitter need to be < 50ns - the transmitter you are looking at only contributes 12ns. 

I will also like to note that under heavier capacitive loading and/or longer bus lengths in the system your max data rate will suffer. However Running this device at 20Mbps is most likely possible depending on chosen receiver and system parameters - but we really don't actually guarantee a max data rate - but realistically for this device is would be > 10Mbps. 

Also as a general rule of thumb - datasheet values are worth more than what we publish on the product pages - the product pages don't have the same level of review over them as a datasheet - so there can be mistakes or even specs listed on product page that aren't in datasheet - they are mostly accurate - but always fall back to datasheet for certainty. 

Please let me know if you have any other questions!

Best,

Parker Dodson

Hi Jenny,

I apologize - but it seems I misunderstood the original ask - a lot of designers use Hz in place of bps - but it seems you are actually using 1Hz = 2bps (which is generally considered the correct way - but both are used) - the reason I bring this is up is because both of the devices listed could hit 20Mbps / 21Mbps - but they are not going to be able to hit 40Mbps/42Mbps which is equivalent to 20MHz/21MHz - you are looking at around 30Mbps or 15MHz on these devices. 

With that being said - those are really our fastest quad channel devices - we really don't have faster devices in quad channel. We do have devices that can meet the required speed - but it would require single channel devices like the THVD1550 or THVD1450 which can meet 50Mbps (25MHz) speeds - but that is the fastest we really offer in RS-485/RS-422 type solutions. The receiver you have chosen should work at those speeds though - but the driver is usually the speed limiter in the system not the receiver. 

Best,

Parker Dodson