Ripamonti [7] talks about two different configurations capable of sub-1 V supply voltage
BGR circuits. The first technique operates by summing two currents with opposite
temperature dependence on a resistor, and the resistor value further controls the reference
voltage. The second technique sums two voltages that are first attenuated, where resistive
voltage dividers are used for the determination of the attenuation factor. The circuit that sums
two currents is given in Figure 2.5.