2 How to Make a TPHL Propagation Delay Measurement With Split Supplies

1. Set one channel of the DC power supply to output a -2.5 V voltage and set its current limit to 100 mA. After ensuring that this channel is disabled, connect GND/VEE to this supply.
2. Set one channel of the DC power supply to output a 2.5 V voltage and set its current limit to 100 mA. After ensuring that this channel is disabled, connect VCC to this supply.
3. Ensure that cables connecting to IN+SENSE, OUT+, and OUT- are matched length and impedance. Perform any deskewing if no matched cables are available. For this setup, IN- is a DC voltage reference so the cables used for IN- and IN- SENSE do not need to be matched.
4. On the signal generator output, set the function generator to produce a square wave output with 100 mVpp at 10-MHz, with a 0 V DC offset. This results in a 50 mV overdrive and 50 mV underdrive. Disable the signal generator output. Connect the signal generator output to IN+.
5. Connect the inverting input, IN-, to ground to establish the threshold for the comparator at 0 V.
6. Connect OUTP and OUTN to a 50-Ω terminated channel on the oscilloscope. Note that with capacitors C7 and C8 populated, the DC component of the outputs will be filtered.
7. Connect IN+SENSE, to another 50-Ω terminated scope channel.
8. Enable the VCC/VEE power supplies.
9. Verify the total supply current is < 30 mA.
10. Enable the signal generator.
11. Monitor and verify the inputs from IN+SENSE and IN- is 0 V DC.
12. Monitor and verify the outputs for OUT+ and OUT-.

Figure 2-2 is a scope shot capture of the inputs and outputs described in the propagation delay procedure. High to Low propagation delay is defined as when the signal generator input (IN+) reaches 0 V to when OUT- reaches 0 V. The propagation delay was measured at approximately 206 ps with the setup described.