I used the HMC311ST89 to amplify the signal which speed is 5Gbps, why its output is negative ,like the input signal is "10011",after amplifying, the output is "01100", is there any other amplifier output positive?
Typical phase of s21 changes with frequency. AT 10 MHz, phase(s21) is around 180 degrees. And at 2.5 GHz, phase is around -100 degrees. That 280 degrees will be spanned from 10 MHz to 2.5 GHz.
That behavior is generally similar among other gain blocks.
You can observe the change in phase vs frequency on the s2p file attached to the product webpage.
For high speed applications, Modulator Drivers are widely used. Check the link below.