Figure 6.

Circuits of our ultralow-power analog silicon neuron. (A–C) Elemental circuits and (D) block diagram. In Equations (30)–(34), I_0P is the current-scaling parameter of common-sized PMOS transistors [M1 in (A), M1 to M3 in (B), and all of the transistors in (C)]. Parameter M_x is the drain current of M1 in (A), which is controlled by V_b. Parameters δ_x (x = v, n) and θ_x (x = v, n, r) correspond to Vdd - V_dlt and Vdd - V_m (Vdd = 1.0 V), respectively. Parameter R_x20 is 1 (0.5) when M6 is on (off) and M7 is off (on) in panel (B). Parameter R_x21 is 1 (2) when M8 is on (off) and M9 is off (on). These two parameters are used to shift the curve of g_x(v) horizontally. The two voltage clamp amplifiers, VAV and VAN, in (D) are for drawing the v- and ñ-nullclines and evaluating r′(n) in Equations (36) and (38). The output of these transconductance amplifiers is 0 when the two input voltages are the same and positive (negative) when the “+” input voltage is higher (lower) than that of the “−” input. When they are activated and the r_n(n) block is deactivated, their outputs are equal to the sums of f_x(v), g_x(v), and I_ax (x = v, n). By scanning V_cv and maintaining V_cn constant, the nullclines are measured. Similarly, when the r_n(n) block is activated and the other blocks are deactivated, the output of VAN is equivalent to r_n(n). By scanning V_cn, the dependence of r_n(n) on n is measured, from which r′(n) can be evaluated. Reprinted with modification from Kohno and Aihara (2014a).