I Think what he's trying to ask, is why digital component power
supplies keep dropping, (1.8V and falling) while the fall in analog
supplies is not so dramatic. I wonder if digital supplies will keep
falling though zero, maybe ending up at -5.2V?
Ok, he could be asking, "Why do analogue designs not use the lower
voltages that are becoming more prevalent in the newer digital designs"
The answer to this, is that is very difficult to get the performance at
For example, a push pull emitter follower will lose two diode drops, say
1.5V, if you want just 1V swing, you would need a 2.5V supply. Rail-rail
designs, using collector outputs, can have stability and bias setting
problems, especially if its cmos, e.g. subthreshold operation often
required. Frequency response is also an issue, as low voltage limits the
ability to use cascodes. Signal to noise and dynamic range is also an
issue. All in all, you don't really want to go below about 5V for an
SuperSpice, a very affordable Mixed-Mode
Windows Simulator with Schematic Capture,
Waveform Display, FFT's and Filter Design.