Welcome to our site! EDAboard.com is an international Electronics Discussion Forum focused on EDA software, circuits, schematics, books, theory, papers, asic, pld, 8051, DSP, Network, RF, Analog Design, PCB, Service Manuals... and a whole lot more! To participate you need to register. Registration is free. Click here to register now.
It doesn't matter whether they are all NMOS or PMOS and NMOS. The thing is that the current source should never be switched off, so it should never happen that all transistors are off, otherwise you have large peaks in your supplies.
You have to drive that block with signals that overlap at high (If they are all NMOS)