Christoph Schenk

Operational Amplifier Applications

Most analog signal processing is done today with circuits using operational amplifiers because opamps are available with good data for little money. Most signals that must be processed in electronic circuits arise in analog form and are needed after processing in analog form also. Therefore analog signal processing is first choice.

Analog Switches and Sample-and-Hold Circuits

An analog switch is designed to switch a continuous input signal on and off. When the switch is in the on-state, the output voltage must be as close to the input voltage as possible; when the switch is off, it must be zero. The principal characteristics of an analog switch are defined by the following parameters: the forward attenuation (the on-state resistance), the reverse attenuation (the off-state current), the analog voltage range, the switching times.

Combinatorial logic circuitry

The term “combinatorial logic network” describes an arrangement of digital circuits which contains no storage elements for the logic variables. The output variables y j are defined by the input variables x i alone, as illustrated by Fig. 9.1. In sequential logic circuits on the other hand, the output variables are also dependent on the state of the system at any time and hence on its previous history.

High-Frequency Amplifiers

Today, in the high- and intermediate-frequency assemblies of telecommunication systems, amplifiers composed of discrete transistors are still used in addition to modern integrated amplifiers. This is particularly the case in high-frequency power amplifiers employed in transmitters. In low-frequency assemblies, on the other hand, only integrated amplifiers are used. The use of discrete transistors is due to the status quo of semiconductor technology. The development of new semiconductor processes with higher transit frequencies is soon followed by the production of discrete transistors, but the production of integrated circuits on the basis of a new process does not usually occur until some years later. Furthermore, the production of discrete transistors with particularly high transit frequencies often makes use of materials or processes which are not (or not yet) suitable for the production of integrated circuits in the scope of production engineering or for economic reasons. The high growth rate in radio communication systems has, however, boosted the development of semiconductor processes for high-frequency applications. Integrated circuits on the basis of compound semiconductors such as gallium-arsenide (GaAs) or silicon-germanium (SiGe) can be used up to the GHz range. For applications up to approximately 3 GHz bipolar transistors are mainly used, which, in the case of GaAs or SiGe designs, are known as hetero-junction bipolar transistors (HBT). Above 3 GHz, gallium-arsenide junction FETs or metal-semiconductor field effect transistors (MESFETs) are used.1 The transit frequencies range between 50 . . . 100 GHz.

Digital-Analog and Analog-Digital Converters

To display or process a voltage digitally, the analog signal must be translated into numeric form. This task is performed by an analog-to-digital converter (A/D converter, or ADC). The resultant number Z will generally be proportional to the input voltage V i :

Sensors and Measurement Systems

Z = V_i /V_{LSB}

DA- und AD-Wandler

where VLSB is the voltage unit for the least significant bit; that is, the voltage for Z = 1.

Appendix: Definitions and nomenclature

This chapter describes the design of transmitters and receivers for radio transmission. The terms used shall have a defined meaning such that the components from the modulator up to the transmitting antenna form the transmitter, while the components from the receiver antenna up to the demodulator form the receiver.