Abstract: This invention provides a circuit and a method for interfacing a subscriber information module, SIM to a base band controller for a mobile phone. It provides voltage level shifting to allow a low voltage base band controller chip to interface to a higher voltage SIM card. The higher voltage bus goes to the SIM card of a mobile phone. The subscriber information module typically contains personal information such as telephone number, identification codes and pin numbers. The circuit of this invention uses active transistor pull-down and pull-up mechanisms. The active pull-up is active for less than one bit time so that the SIM card sees only a 20 kilo ohm resistor allowing performances equal to or better than ISO7816 specifications.

Abstract: This invention provides a circuit and a method for interfacing a subscriber information module, SIM to a base band controller for a mobile phone. It provides voltage level shifting to allow a low voltage base band controller chip to interface to a higher voltage SIM card. The higher voltage bus goes to the SIM card of a mobile phone. The subscriber information module typically contains personal information such as telephone number, identification codes and pin numbers. The circuit of this invention uses active transistor pull-down and pull-up mechanisms. The active pull-up is active for less than one bit time so that the SIM card sees only a 20 kilo ohm resistor allowing performances equal to or better than ISO7816 specifications.