the n channel mos transistor 7 is arranged so as to connect a gate to a drain and also to connect a p type substrate to a source the node or point of connection 6 of the gate of the n channel mos transistor 5 and the gate of n channel mos transistor 7 is connected to the node or point of connection 8 of the source of n channel mos transistor 5 and the drain of n channel mos transistor 7 in the embodiment shown in fig2 a constant voltage is obtained between the node 8 and the terminal v ss the constant voltage is only slightly changed by a change in the source voltage applied across the terminals v dd and v ss or by a temperature change fig3 illustrates a graph showing a relationship between the current and the voltage of the circuit illustrated in fig2 for a mos transistor which is under a saturation condition the relationship will be defined by equation 1 assuming that the threshold voltage of the depletion type n channel mos transistor 5 is v t5 current i 5 of the n channel mos transistor 5 and current i 7 of the n channel mos transistor 7 are given by the following equations 2 and 3 respectively wherein v g5 and k 5 are source gate voltage of the transistor 5 and its coefficient of conductivity wherein v g7 k 7 and v t7 are source gate voltage coefficient of conductivity and threshold voltage of the transistor 7 respectively since the i 5 is equal to the i 7.