FEATURES OF THE CIRCUITRY OF OPERATIONAL AMPLIFIERS BASED ON COMPLEMENTARY FIELD-EFFECT TRANSISTORS WITH A CONTROL PN-JUNCTION
The systematic component of the offset voltage (Voff) of two-stage BJT and CMOS operational amplifiers (Op-Amps) with classical architecture significantly depends on the numerical values (difference from unity) of the current transfer coefficient (Ki≈1) of the current mirrors (CM) used. This parameter of CM is also influenced by the Earley stress of their dominant active components. Current JFET mirrors are today a weak link in modern JFET analog circuitry and they are impractical to use in the structure of JFET Op-Amps. The article posed and solved the problem of the conditions for the elimination of CM in an Op-Amps based on field-effect transistors with a control pn-junction for the case when it is necessary to obtain a small Voff. Variants of practical circuits of input (InS) and intermediate (IntS) stages of microelectronic operational amplifiers based on complementary field-effect transistors with a control pn-junction (CJFET) are proposed. Their main feature is the absence of a current mirror, which, when implemented on a CJFET, negatively affects the main parameters of the Op-Amps in terms of the systematic component of the offset voltage, the attenuation coefficients of the input common-mode signal, and the suppression of noise on the power buses. In this regard, InSs and IntSs circuits are promising, which do not use this CJFET functional unit. The circuits of Op-Amps based on the developed InSs with an open gain of more than 80 dB and a systematic component of the offset voltage within 300 μV with low current consumption in a static mode are presented. The relevance of the performed studies lies in the need to develop the theory of designing high-precision JFET and CJFET IP-modules for use in structures of low-noise analog interfaces of sensors of various physical quantities, including those operating in severe operating conditions (exposure to low temperatures and radiation) The proposed circuits can be implemented on wide-gap semiconductors (SiC JFET, GaN JFET or GaAs JFET).