Negative power supply or Ground?

[lunren]

Hi,all,

We are going to design a gate driver for LCD. We have two positive power supplies, negative power supply and ground. The inputs are normal digital signals, the output is level shifted signal(higher voltage). Now the problem is which one should the substrate be connected to, negative power supply or ground?

 

[sunking]

it depend on your process and the output logic voltage level.
give more detail

 

[adedia]

if your digital input signal level was +1v for logic '1'
and -1 for '0'

then used negative power...
if not used ground instead

 

[lunren]

So far, we don't know it is single well or double well process.
For single well, there is problem if we connect substrate to ground because the parasitic pn junction will conduct. But if we connect substrate to negative power supply(-5V~-15V), then the threshold (for NMOS in digital part) may be too high due to bias effect.
The output voltate level is: +40V for '1', -5V~-15V for '0'. The input voltage level is: 2.3V~3.6V for '1', 0V for '0'.

 

[sunking]

it should be true double well process, and most likely high voltage bicmos process

So the substrate of low voltage device will connect to ground, while the some high voltage will to negative supply. These depond on you circuit structre.

 

[tsanlee]

For negative power supply, you can use the charge pump circuit , but it need some external MOS.

In P-sub process,the negative voltage will turn on the body diode of NMOS .