A modified band-gap circuit capable of producing programmable output differential reference voltage is described. Analysis of the effects of the amplifier noise and offset on the reference voltage is performed, obtaining a compact formula of general validity. A prototype, based on a switched capacitor amplifier with continuous time output, has been designed using the UMC 0.18 um CMOS process. The circuit produces three digitally selectable output differential voltages in the range 1.22-2.8V and is capable of sourcing/sinking currents up to of 1 mA. Electrical simulations show that the temperature stability is 38 ppm/°C while the standard deviation of output voltage spread is nearly 0.4%.