This paper describes a voltage reference circuit based on composite transistors and operating in weak inversion mode. The voltage reference was fixed in 100mV and the supply voltage can be as low as 0.8V. The weak inversion allows small current too leading the total power in the nW range. Simulation results points to a deviation (3σ and process corner) less than ±1%. The reference is indicated to be used in biomedical applications specially those that use implanted devices. In these cases the temperature impact is minimized since the human body has an effective biological system to keep it constant at about 37°C.