Oscillator using dual output current controlled transmitter

In the past decade, engineers have made great efforts to design and implement current-mode circuits using second-generation current conveyors, which have higher signal bandwidth, better linearity, larger dynamic range, simpler circuits, and lower power consumption than their predecessors. Recently, the second generation of dual-output current-controlled conveyors has appeared. This device is an active building block (Figure 1) and is characterized by the following equations: IY=0, VX=VY+IXRX and IZ+=IX, IZ–=–IX. The parasitic resistance at terminal X is RX=(VT/2IB), where VT is the thermal voltage and IB is the conveyor bias current that can be adjusted within a few dozen times.

Figure 2 shows a current controlled oscillator with a small number of components. It uses only two dual-output current controlled transmitters and two capacitors to ground. These devices have no external resistors, and the parasitic resistance at terminal X is the resistance. The proposed circuit design provides the ability to electronically control the oscillation frequency.

The characteristic equation for the two circuits in Figure 2 is: s2C1C2RX1RX2+sC2RX1–sC1RX1+1=0. The conditions required for the oscillation to meet the Barkhausen criterion (i.e., the loop gain is 1 or above and the feedback signal back to the input is shifted by 360°) are: C1=C2 and the oscillation frequency is f =1/(2π[U1]).

Assuming C1 = C2 = C, and taking RX1 = RX2 = VT/2IB, we get the oscillation frequency: f = IB/πCVT. Obviously, the DC bias current IB can change the frequency of the current conveyor, so the frequency is electrically controllable.