A transmitter has much-less challenging task than the receiver. The former operates on a higher-level, known signal in a known setting, while the latter must find and decode a largely unknown signal corrupted by internal and external noise, interference from other signals, distortion, low signal levels, and constantly changing parameters. This FAQ looks at the […]
RS-232 and related standards, Part 1
High-speed, high-performance “just plug and go” wired-communications interfaces such as Ethernet and USB are in wide use. In contrast, the technically ancient RS-232 standard and related standards seem like antique museum pieces with no design-in interest. However, that is a simplistic view of the reality. Although not necessarily the first choice or obvious choice in […]
IBIS model: How can it help with signal analysis?
An Input Output Buffer Information Specification (IBIS) model is a standard in the semiconductor industry for modeling semiconductor devices from a behavioral perspective, for both analog and digital perspectives. IBIS modeling enables engineers to describe detailed signal behavior in a circuit design without revealing proprietary information about the circuits (or the processes used to make […]
Current feedback amplifiers, Part 2
Part 1 of this FAQ look at the operation of the CFB op amp and compared it to the VFB op amp. Part 2 continues the discussion of these two op amp topologies and their characteristics. Q: How do you choose between VFB versus CFB? A: Today’s CFB and VFB amplifiers have comparable performance, but […]
Current feedback amplifiers, Part 1
Almost every engineer who has to deal with real-world signals, analog sensors, front-end circuitry, filtering, line drivers/receivers, or general amplification is familiar with the basic operational amplifier (op amp) which is the building block of most analog circuity. These op amps generally use voltage feedback (VFB), and have been studied and used extensively. However, there […]
Eye and Constellation Diagrams, Pt 2
Part 1 looked at the eye diagram, a simple yet powerful visual tool which reveals many specifics about the quality of a recovered bit stream. Part 2 looks at the constellation diagram, another powerful visual tool which is used to show the signal space of complex encoding schemes and relationship among the symbols. Q: Why […]
Eye and Constellation Diagrams, Pt 1
Digital signals representing data symbols may be presumed to be clean, consistent representations of ones and zeroes when they are launched onto their communications medium, whether it is a wired, wireless RF, or optical fiber link. However, due to bandwidth limitations of the medium, external and internal noise, crosstalk, multipath, reflections, and many other unavoidable […]
Impedance matching and the Smith Chart, Part 2
Part 1 looked at impedance matching and the need for a complex conjugate impedance at the load, compared to the source impedance. Once the need for an impedance-matching network is determined – and it is very likely needed – the next challenge is defining and creating this network. It may seem that doing a few […]
Using the Smith chart for Impedance matching, Part 1
In circuit designs spanning low-frequency audio through high-frequency RF, there’s considerable discussion about impedance matching between components or subcircuits, with various tools such as the Smith chart with is used to facilitate the matching. Q: What is impedance matching? A: Impedance matching means that a signal source sees a load impedance which is the complex […]
Why use a nonlinear amp?
Users normally place a great deal of value in the high linearity of an amplifier and its corresponding low distortion. Audio amplifiers, for example, are quoted with many linearity specifications, such as total harmonic distortion (THD) or 1%, 0.1% or even less. Even the outputs of amplifiers with internal topologies which are inherently nonlinear, such […]
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