integrated H-Bridge circuit equivalent for low resistive loads

[engrMunna]

Hi,
Referring to the figure, the transistors can turn on only in pairs that is either 1 and 4 are on or 2 and 3 are on. So this circuit is an H-Bridge for the R load. And the polarity of the voltage across R is determined by which pair of transistors is on. Now the problem is that R is very low about 200 ohms. I have to build this as an integrated circuit, and I don't want to use large transistor sizes (width of the transistor). Suppose my Supply is of 3 volts and I need a drop of 1 Volt across R, then the channel resistance of Mosfets should be comparable in value with R. And for a channel resistance of around 200 ohms for MOS in 180nm Technology, the transistors have to be unreasonably large. Also for a drop of 1 volt across R, I need a current of 1/200 amps. so for integrated circuits in 180nm this is not reasonable. Can some one suggest an alternative circuit for doing this? A person told me to think about using Current Starved Voltage sources...I don't know how they will help in this case, because for a drop of 1V across a 200 ohm resistance you need definetly need 1/200 amps? I mean this is not possible that you get 1V across R and have a current less than 1/200 amps flowing through R?
Thanks

 

[FvM]

I agree to your deducions from ohms law.

Talking about channel resistance isn't quite correct, because the transistors won't necessarily operate in ohmic region. In addition, the output current will vary considerably according to process, voltage and temperature effects. I think that asymetric current mirrors would be better suited to achieve a defined output current.