In the last decade, engineers have done much work in designing and implementing current-mode circuits using second-generation current conveyors, which have higher signal bandwidth, greater linearity, larger dynamic range, simpler circuitry, and lower power consumption than their predecessors. Recently, a second-generation dual-output, current-controlled conveyor has emerged. The device is an active building block (Figure 1), and the following equations characterize it: I_Y=0, V_X=V_Y+I_XR_X, and I_Z+=I_X; I_Z–=–I_X.The parasitic resistance at terminal X is R_X=(V_T/2I_B), where V_T is the thermal voltage and I_B is the bias current of the conveyor that is tunable over several decades.

Figure 2 shows current-controlled oscillators with few components, employing only two dual-output current-controlled conveyors and two grounded capacitors. The devices use no external resistors, and the parasitic resistance at terminal X realizes resistance. The proposed design for the circuit provides electronic controllability of frequency of oscillation.

The characteristic equation for both of the circuits in Figure 2 is s²C₁C₂R_X1R_X2+sC₂R_X1–sC₁R_X1+1=0. Satisfying Barkhausen’s criteria—that the loop gain is unity or greater and that the feedback signal arriving back at the input is phase-shifted 360°—the required condition for oscillation is C₁=C₂, and the frequency of oscillation is f=1/(2π).

Assuming that C₁=C₂=C and taking R_X1=R_X2=V_T/2I_B yield a frequency of oscillation: f=(I_B/πCV_T). Clearly, the dc-bias current, I_B, can vary the frequency of the current conveyors, and the frequency is, therefore, electronically controllable.