Development, modeling and research of an amplifier without passive elements using JFETs

Abstract

It is known that an analog buffer, or voltage repeater buffer, is an electronic circuit based on an operational amplifier or active element with a gain of unity (K=1). Ideally, it should transfer the input voltage to the output without changes in amplitude and phase, while providing high input and low output impedance for matching the cascades. Also, an essential task is to provide a given output power.

The main functions of an analog buffer are: cascade isolation (prevents the influence of the output load on a sensitive signal source); impedance matching (effectively transmits a signal from a source with high internal resistance to a low–impedance input, such as an ADC); dropout protection (allows you to transmit an analog signal over long cables without distortion and voltage drop).

The aim of the work is to investigate the possibility of building a buffer on discrete components without using passive elements (resistors, capacitors, inductors). This buffer can be used for both analog and digital signals. The task of building such a circuit that uses only active components (hereinafter PAA pure active amplifier) is promising.

PAA has advantages such as: 1) Minimum area on the crystal. Resistors and capacitors take up a lot of space in silicon. Transistors are much more compact; 2) Wide bandwidth. The absence of parasitic capacitances of large passive elements increases the speed and operating frequency. High input impedance. Ideal for isolating the signal source from subsequent stages. Low output impedance. Allows you to effectively control heavy capacitive loads; 3) Manufacturing processability. Manufacturing a circuit consisting only of transistors simplifies and reduces the cost of microcircuit lithography; 4) Low noise. Thermal noise of resistors (Johnson noise) is absent in such a structure.

A series of laboratory studies were conducted on the operability of the developed PAA (pure active amplifier) buffer circuit, and its parameters were also measured. The circuit showed its operability and can be used in tasks where cascade decoupling, impedance matching, signal dropout protection at small sizes of what? and low cost are required.

In the future, with further experiments, it is possible to use it to create integrated circuits, where the main advantages will be: minimal area on the crystal, wide bandwidth, manufacturability of production and low noise level.