High-Speed Operational Amplifier Based On Complementary “Folded” Cascodes

A significant disadvantage of classical operational amplifiers with a complementary “folded” cascode is that in the dynamic overload mode of the input differential stage, the maximum output current of the “folded” cascode is tightly coupled to the currents of the current-stabilizing bipoles that establish its static mode. This prevents (under the static current consumption limitations of the operational amplifier) a fast recharge of the integrating correction capacitor, which limits the maximum slew rate of the output voltage. The paper discusses new circuit solutions of CBJT operational amplifier based on complementary “folded” cascodes and input differential stage of dual-input stage subclass to increase slew rate from 215 V/µs to 8000 V/µs level. The problem solved here is to provide higher levels of “folded” cascode output current during the transient edge. This effect is achieved by introducing three additional small capacitance correction capacitors into the circuit. It is possible to introduce a special current limiting resistor in series with the third additional capacitor to reduce overshoot during the transient edge. The proposed modifications of operational amplifier have significant advantages in comparison with the classical ones based on complementary “folded” cascodes in terms of slew rate level. Results of computer modeling of the operational amplifier in LTSpice environment for silicon CBJT technological process with micron topological norms are presented.