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SN74AXC4T774-Q1: Output distorted while feeding in a 100MHz Signal

Part Number: SN74AXC4T774-Q1
Other Parts Discussed in Thread: TXV0106-Q1, SN74AVC4T774-Q1

Tool/software:

Though the datasheet claims speed of 310Mbps while converting 1.8V to 3.3 V signal, the measured data comes no where close to this. What could be happening here?

Schematics:

IN:

Out: Measured with an active probe terminated with 50 Ohms

  • Hi Darshan,

    I suspect the total lumped capacitance is above 15 pF similar to table 6-1 of datasheet.

    This can be verified by disconnecting all loads and measuring as close to the device pin as possible with similar probe used for IN, thanks.

    Best Regards,

    Michael.

  • Not much improvement:

    Modified Schematics: 

    NEW: Capture at pin 12, active probe capacitance is 0.6pF

  • Also, the conversion is from 1.8V to 1.1V - not sure if that's contributing to it and all 4 channels are being used. 

  • Hi Darshan,

    Yes, it is contributing as I see significant improvement i.e. device is translating and high level is reaching 1.1 V as opposed to previous waveform.

    Data sheet shows tpd of about 12 ns for 1.8 V to 1.1 V, roughly indicating 83 Mbps as 42 MHz (i.e. 1/tpd). You may confirm by observing waveform for 42 MHz per the 1.1 V and increasing back to 100 MHz for VCCB up to 3.3 V showing the contribution as higher voltages support higher speeds compared to smaller voltages.

    You may also see SN74AVC4T774-Q1 tpd indicating a rough estimate for 83 MHz (note that using tpd is a low estimate as reference), or TXV0106-Q1, thanks.

    Best Regards,

    Michael.

  • Hi Michael,

    Thanks for explanation, appreciate it!

    Is there an alternate device(preferably pin compatible) that supports 100Mhz?

    Thanks,

    Darshan

  • Hi Darshan,

    The SN74AVC4T774-Q1 recommendation would be the only exact P2P alternate recommendation. 

    I would recommend AVC as the best solution for the translation. Please further note that data rates can be characterized by their VOH/VOL levels. Hence, no level shifter concerns if the logic levels are met, thanks.

    Best Regards,

    Michael.

  • Thanks Michael for your prompt response, we tested with SN74AVC4T774-Q1 and the results did improve significantly, we shall proceed with it!