TABLE OF CONTENTS Walt Kester
Components used in the signal path in communications systems must have wide dynamic range at high frequencies. Dynamic range is primarily limited by distortion and noise introduced by the active elements in amplifiers, mixers, and so forth. In the past, amplifiers for communications applications consisted primarily of "gain blocks" with appropriate specifications. Typically such amplifiers are specified for gain, bandwidth, distortion, and so forth, as a system is designed, and purchased as a self-contained package. This package itself is actually a communications amplifier subsystem.
Today, however, op amps with bandwidths of hundreds of megahertz, low noise, high dynamic range and flexible supply voltages also make popular building blocks in communications systems. They are easily configured for a given gain, and can deliver good performance.
As a necessity, this means that high frequency op amps must be fully specified not only in terms of traditional op amp ac specifications (bandwidth, slew rate, settling time), but also in terms of communications-specific specifications. These latter specifications would include performance for harmonic distortion, spurious free dynamic range (SFDR), intermodulation distortion, intercept points (IP2, IP3), noise, and noise figure (NF). Figure 6-121 illustrates these specifications.
Noise
Noise referred to input (RTI)
Noise referred to output (RTO)
Distortion
Second and third order intercept points (IP2, IP3)
Spurious free dynamic range (SFDR)
Harmonic distortion
Single-tone
Multi-tone
Out-of-band
Multitone Power Ratio (MTPR)
Noise Factor (NF), Noise Figure (NF)
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