Why THS6002 Vo can't output same as THs4631 ?
The first thing to note is that the THS6002 has both input and output voltage ranges. According to page 4 of the THS6002 datasheet, the input common mode range on a +/-15V supply is +/-13.4V min or +/-1.6V away from the rails. The single ended output swing similarly is +/-3.5V away from the rails. For a 0V to 15V setup, this would translate to about 1.6V to 13.4V input range and 3.5V to 12.5V output range. A 4Vpp input signal and 2V DC offset will be violating the low side input common mode range spec, and with a gain of 2.54V/V, the output ideally would be sitting at 5.08V DC offset and 10.16Vpp which would also violate the output common mode spec. However, if you've already violated the input common mode spec and input gets clipped on the low side, the DC level of the signal would be shifted up which in turn would cause your output to be sitting at a much higher DC voltage and thus potentially violating the output common mode spec on the high side . This looks like what you are seeing for the THS6002 case. If you add a negative rail to give yourself more margin, you can get by without these problems.
For the THS4631, the same concerns apply. Refer to page 4 of the THS4631 datasheet for the input and output voltage ranges.
Regards,Luke LapointeHigh Speed Amplifiers
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