[SOLVED] Thevenin model of D flip flops

[grit_fire]

Hi, all,

What should be the correct Thevenin model for a D flip flop? Is the swing of output from 0 to VDD? How about the source impedance? Is it very low since the output swing is from 0 to VDD?

Thank you!

 

[crutschow]

It depends upon the type of D FF. The output impedance would be low but generally non-linear. You can infer the impedance from the data sheets for the FF.

 

[grit_fire]

It depends upon the type of D FF. The output impedance would be low but generally non-linear. You can infer the impedance from the data sheets for the FF.

Thank you, yes, that make sense.

I am looking at the DFF from TI: https://www.ti.com/lit/ds/symlink/sn74aup1g74.pdf. could you be a little more specific on how to infer the impedance from the datasheet? I couldn't find relevant information inside. thanks!

 

[crutschow]

If you look at the table on page 5 you will see that for supply voltages of 2.3V and 3V they give the output voltages for two different output currents. From the differences in output voltage versus output current you can calculate the Thevenin output impedance. It will likely be different for the two supply voltages and perhaps also for the low output versus the high output.

 

[grit_fire]

If you look at the table on page 5 you will see that for supply voltages of 2.3V and 3V they give the output voltages for two different output currents. From the differences in output voltage versus output current you can calculate the Thevenin output impedance. It will likely be different for the two supply voltages and perhaps also for the low output versus the high output.

Ah.. that's brilliant. Thanks for sharing this!