Oscillation-Free Current Source Bias With Compensation
Original Publication Date: 1988-Oct-01
Included in the Prior Art Database: 2005-Feb-15
A circuit modification to a standard current mirror provides a stable voltage reference for large fanouts used in circuitry for semiconductor devices. The proposed circuit incorporates a feedback loop which permits the large fanouts and avoids oscillations. Common types of current mirrors used in array designs are shown in Figs. 1-3. The standard mirror, as originally proposed by Widlar, Fig. 1, has I mirrored into the load transistors for small fanouts and large b. The mirrored current Ic is approximately equal to [b/(b+n+1)], where n is the number of base nodes. When n is large and b is low, the mirror will not function as intended. Fig. 2 is a variation for large fanouts where an emitter follower is added to provide the drive.