Negative Feedback in Electronics

Lead Image Novacek

A Look at the Opposite Side

Besides closed-loop control systems, negative feedback is found in many electronic circuits—especially in amplifiers. And just like positive feedback, negative feedback can significantly change or modify a circuit’s performance.

By George Novacek

Following last month’s discussion of positive feedback, let’s now take a look at its opposite: the negative feedback. Besides closed-loop control systems, it is found in many electronic circuits, especially in amplifiers. As we have already seen, feedback significantly changes or modifies a circuit’s performance. The end of the 19th century and the beginning of the 20th century was the era of introduction of the telephone. For long distance calls, amplifiers were needed along the telephone lines to make up for their transmission losses.

Vacuum tube amplifiers of the day suffered from many ailments: drift, high distortion and generally poor performance, making the long-distance voice communications nearly unintelligible. Harold Stephen Black, an AT&T engineer, was one of many working to solve this problem. Eventually—because he was familiar with the effects of negative feedback in mechanical systems—he tried to apply it to a vacuum tube amplifier. The result was astonishing and amplifiers with negative feedback have been with us ever since.

FIGURE 1 Transfer function of an operational amplifier with negative feedback

FIGURE 1
Transfer function of an operational amplifier with negative feedback

The op amp is the epitome of feedback application in electronic circuits. Because its comprehension is valid for all electronic feedback circuits, let’s take a closer look at the op amp. To analyze the negative feedback mathematically, we’ll consider an amplifier as a combination of two functional blocks: The open loop gain (OLG) block with transfer function A(s) and the feedback block with transfer function β(s). With monolithic amplifiers, the feedback is usually applied externally. The overall transfer function follows the principle shown in Figure 1.. …

Read the full article in the November 328 issue of Circuit Cellar

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Analog ICs Meet Industrial System Needs

Jeff Lead Image Analog Inustrial

Connectivity, Control and IIoT

Whether it’s connecting with analog sensors or driving actuators, analog ICs play many critical roles in industrial applications. Networked systems add new wrinkles to the industrial analog landscape.

By Jeff Child

While analog ICs are important in a variety of application areas, their place in the industrial market stands out. Industrial applications depend heavily on all kinds of interfacing between real-world analog signals and the digital realm of processing and control. Today’s factory environments are filled with motors to control, sensors to link with and measurements to automate. And as net-connected systems become the norm, analog chip vendors are making advances to serve the new requirements of the Industrial Internet-of-Things (IIoT) and Smart Factories.

It’s noteworthy, for example, that Analog Devices‘ third quarter fiscal year 2017 report this summer cited the “highly diverse and profitable industrial market” as the lead engine of its broad-based year-over-year growth. Taken together, these factors all make industrial applications a significant market for analog IC vendors, and those vendors are keeping pace by rolling out diverse solutions to meet those needs.

Figure 1

Figure 1 This diagram from Texas Instruments illustrates the diverse kinds of analog sub-systems that are common in industrial systems—an industrial drive/control system in this case.

While it’s impossible to generalize about industrial systems, Figure 1 illustrates the diverse kinds of analog sub-systems that are common in industrial systems—industrial drive/control in that case. All throughout 2017, manufacturers of analog ICs have released a rich variety of chips and development solutions to meet a wide range of industrial application needs.

SOLUTIONS FOR PLCs

Programmable Logic Controllers (PLCs) remain a staple in many industrial systems. As communications demands increase and power management gets more difficult, transceiver technologies have evolved to keep up. PLC and IO-Link gateway systems must dissipate large amounts of power depending. That amount of power is often tied to I/O configuration—IO-Link, digital I/O and/or analog I/O. As these PLCs evolve into new Industrial 4.0 smart factories, special attention must be considered to achieve smarter, faster, and lower power solutions. Exemplifying those trends, this summer Maxim Integrated announced the MAX14819, a dual-channel, IO-Link master transceiver.

The architecture of the MAX14819 dissipates 50% less heat compared to other IO-Link Master solutions and is fully compatible in all modes for IO-Link and SIO compliance. It provides robust L+ supply controllers with settable current limiting and reverse voltage/current protection to help ensure robust communications with the lowest power consumption. With just one microcontroller, the integrated framer/UART enables a scalable and cost-effective architecture while enabling very fast cycle times (up to
400 µs) and reducing latency. The MAX14819 is available in a 48-pin (7 mm x 7 mm) TQFN package and operates over a -40°C to +125°C temperature range.  …

Read the full article in the November 328 issue of Circuit Cellar

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Note: We’ve made the October 2017 issue of Circuit Cellar available as a free sample issue. In it, you’ll find a rich variety of the kinds of articles and information that exemplify a typical issue of the current magazine.