Високолінійні буфери напруги для високопродуктивних АЦП і ЦАП

Abstract

The article analyzes the proposed methods of structural and functional organization of highly linear voltage buffers built according to two-stroke symmetrical structures. In the first method, it is assumed to increase the resistance of the current outputs. Thanks to this, it is possible to stabilize the collector-emitter junction voltage of the transistors of the output stages. In the second method, it is proposed to re-duce the influence of the base current of the transistors of the output stages, which will reduce the linearity error. In the third method, it is proposed to increase the linearity without reducing the speed level, by stabilizing the collector-emitter voltages of the output stages. It is shown that the use of voltage stabilization of the collector-emitter transitions makes it possible to improve the circuit characteristics by 1÷2 orders of magnitude. Analytical dependencies describing the linearity errors of the cores of voltage buffers, which are built according to a two-stroke symmetrical structure, are derived. It is shown that the proposed approaches allow to reduce the errors of linearity and zero shift by an order of magnitude or more. To determine the components that affect the appearance of the error, an equivalent scheme for replacing the output of the voltage buffer core is considered. It was determined that the proposed methods of building voltage buffers have a common drawback, namely, low load capacity, which is determined by the output resistances of the circuits. An approach that allows increasing the load capacity of voltage buffers is considered. It is shown that it makes it possible to reduce the output resistance by 2÷3 orders of magni-tude. In order to increase the load capacity and maintain the specified linearity of the voltage buffer scheme, it is proposed to supplement it with a two-stroke two-channel current amplifier. The use of the proposed methods and approaches for the construction of voltage buffers allows obtaining such devices that have the necessary characteristics and can be used as part of high-performance ADCs and DACs