Circuitry of Operational Amplifiers with CMOS and JFET Input Differential Stages without Classical Reference Current Sources

It is shown that in the classical operational amplifier with input stage of dual-input-stage subclass the current error in the high-impedance node is determined not only by the scatter of current mirror transfer coefficients, but also by the non-identicality of reference current sources establishing the static mode. Therefore, the operational amplifiers of the class under consideration have two corresponding components of the zero bias voltage. We propose new circuit solutions of differential stages on CJFET (or CMOS transistors with integrated channel), which do not contain in their structure classical reference current sources, negatively affecting in typical differential stages the zero bias voltage, the attenuation coefficient of input in-phase signals, the power supply noise suppression coefficient and the upper boundary frequency. A wonderful feature of the proposed differential stage is the ability to operate in class-AB mode. This property contributes to the increase of the operational amplifier performance in the large-signal mode. The equations for the main components of the zero bias voltage in the operational amplifier based on the differential stage of the considered subclass are obtained, taking into account the current transfer errors of the applied current mirrors. The results of modeling of the operational amplifier with one integrating correction capacitance on CJFET transistors in LTspice environment are presented, which show that the investigated circuit provides a voltage gain of about 80 dB. However, with high requirements to the zero bias voltage it should use precision current mirrors, as in classical dual-input-stage operational amplifiers.