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Related Posts
Blog Post:
Grounding Principles
Bruce Trump
In a previous blog on supply bypassing , I cautioned that poor bypassing could increase distortion of an amplifier. A reader, Walter, asked an interesting question… where should you connect the ground of a bypass capacitor to avoid problems? This raises questions regarding proper grounding...
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May 21, 2013
Blog Post:
Handy Gadgets and Resistor Divider Calculations
Bruce Trump
Handy gadgets make our engineering life easier—the little special purpose computer programs or spreadsheets that you might find or create yourself. Back in the old days, engineers used nomographs. These are graphical aids that solve common multivariable problems of all sorts. Calculators and...
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May 14, 2013
Blog Post:
Chopper Op Amps—are they really noisy?
Bruce Trump
Chopper op amps offer very low offset voltage and dramatically reduce low frequency 1/f (flicker) noise. How do they do it? Here’s a quick-read on the tricks. Click Here to read on EDN Magazine site.
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May 6, 2013
Blog Post:
Bypass Capacitors… yes, but why?
Bruce Trump
Everyone knows that op amps should have power supply bypass capacitors located near the IC’s terminals, right? But why? Why, for example, is an amplifier more apt to oscillate without proper bypassing? The reasons will increase your understanding and awareness. Power supply rejection is an amplifier’s...
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Apr 23, 2013
Blog Post:
Rail-to-Rail Inputs—what you should know!
Bruce Trump
Rail-to-Rail (R/R) op amps are extremely popular, especially useful with low supply voltage. You should know how R/R inputs are accomplished and understand some trade-offs. Figure 1 shows a typical dual-input R/R stage comprised of both N and P-channel transistor pairs. The P-channel FETs handle the...
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Apr 16, 2013
Blog Post:
Op Amps… G=1 stable & decompensated
Bruce Trump
You have voted. Unity-gain-stable op amps won in a landslide—they’re far more popular than decompensated op amps. What’s this all about? Click Here to read on EDN Magazine site.
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Apr 8, 2013
Blog Post:
Paralleling Op Amps—is it possible?
Bruce Trump
Is it possible to parallel two op amps to get twice the output current? We get this question periodically on our E2E forums. Though we may answer with a qualified “yes,” it tends to make us shudder just a bit. It can be done… but with great care. So let me come quickly to a key...
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Mar 26, 2013
Blog Post:
Resistor Puzzle—the sequel
Bruce Trump
It’s time for some fun! I’ve known a few folks who have tormented colleagues with a resistor cube—equal resistors on all sides. So in case you’ve solved that one, let’s add a twist. In this cube, not all the resistors are equal. The resistance from A to B is 1Ω. Resistor...
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Mar 12, 2013
Blog Post:
1/f Noise—the flickering candle
Bruce Trump
The 1/f (one-over-f) low frequency noise region of amplifiers seems just a bit mysterious. Reader “tweet” asked for a discussion of 1/f noise—a challenging topic for a short blog. Click Here to read on EDN magazine web site. Excel noise calculation file here… (Please visit...
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Mar 3, 2013
Blog Post:
Simulating Gain-Bandwidth—the generic op amp model
Bruce Trump
It may not always be obvious how the gain-bandwidth product (GBW) of an op amp may affect your circuits. Macro-models have a fixed GBW. Though you can look inside these models, it’s best not to tinker with them. What to do? You can use a generic op amp model in SPICE to check your circuits for...
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Feb 26, 2013
Blog Post:
ESD… Zapp!
Bruce Trump
We’ve included device-level ESD performance of our ICs in data sheets for many years. But these figures apply to an integrated circuit before soldering onto your circuit board. What about ESD tolerance on your PCB ? We qualify the ESD performance by zapping each pin multiple times on several...
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Feb 19, 2013
Blog Post:
Op Amp Noise—but what about the feedback?
Bruce Trump
Last month we explored noise of the non-inverting amplifier but I dodged the issue of the feedback network’s noise contribution. A reader, Jim, challenged me—he wanted more detail. So what about the noise from the feedback network? Click Here to read on EDN magazine web site. Excel...
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Feb 10, 2013
Blog Post:
The Inverting Attenuator, G = -0.1… is it unstable?
Bruce Trump
Unity-gain-stable op amps are stable in a gain of one or greater, but not less, right? What to do? This question appears on our E2E forums periodically. Okay, here’s the short answer… an inverting attenuator is stable! You want to know why, right? There are a couple of ways to look...
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Feb 5, 2013
Blog Post:
Put Gain Up Front—waxing philosophical
Bruce Trump
Low noise, low offset voltage, low drift—all the precision low-level signal processing goals get easier when you put voltage gain up front in the signal chain. It’s a simple concept. The error in the second stage is divided by the gain of the first stage, figure 1. For example, with only...
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Jan 22, 2013
Blog Post:
Input Capacitance—common-mode?...differential?… huh?
Bruce Trump
The input capacitance specifications of op amps are often confused or ignored. Let’s clarify how these specs can best be used. Stability of an op amp circuit can be affected by input capacitance at the inverting input by causing phase shift—a delay of the feedback reaching the inverting...
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Jan 15, 2013
Blog Post:
Op Amp Noise—the non-inverting amplifier
Bruce Trump
Building on last month's discussion of resistor noise, let’s check out some basics of amplifier noise. The non-inverting op amp configuration is most common for low noise applications so we’ll make that the focus. Click Here to read on EDN magazine web site. Other interesting...
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Jan 7, 2013
Blog Post:
Holiday Brain Teaser
Bruce Trump
Here’s a little resistor puzzle to keep your mind sharp over the holidays. What is the resistance of this infinite resistor network? This can be solved numerically (and very accurately) but for this puzzle that’s considered cheating. Find the closed-form solution . And another challenge...
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Dec 24, 2012
Blog Post:
Breadboarding with Micro-Packages—Ouch!
Bruce Trump
Have you noticed?...it’s rare to find new generation op amps and other ICs in DIPs (dual-inline packages). Without volume demand, it’s not economically viable to offer new ICs in DIPs. Breadboarding with these newer fine-pitch micro-packages can be a pain. What to do? This DIP adapter...
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Dec 18, 2012
Blog Post:
PCB Layout Tricks—striped capacitors and more
Bruce Trump
I posed a question a couple of weeks ago regarding film capacitors—what’s the meaning of the stripe on one end? Check the picture below. These are non-polarized capacitors so it’s not a polarity marking. A reader, Richard, answered correctly—it identifies the outside conductive...
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Dec 11, 2012
Blog Post:
Resistor Noise—reviewing basics, plus a Fun Quiz
Bruce Trump
The noise performance of amplifier circuits is greatly affected by the Johnson noise of resistors—the source resistance and feedback resistors. Most everyone seems to know that resistors have noise but may be a bit foggy on some of the details. Here’s a bite-sized review in preparation for...
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Dec 3, 2012
Blog Post:
The Unused Op Amp—what to do?
Bruce Trump
I’m not referring to op amps in your parts bin. Those should be in anti-static bags or conductive foam. What about the one on your circuit board—the unused op amp in a quad or dual package. Hummm?? A recent question on our forums spurred me to address this subject but in the process, I...
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Nov 27, 2012
Blog Post:
Temperature Effects on Input Bias Current… plus a Random Quiz
Bruce Trump
Last week we looked at the source of input bias current in CMOS and JFET amplifiers, finding that it comes from the leakage of one or more reverse-biased P-N junctions. Check it out if you missed it. We ended with a caution that these leakages increase significantly with temperature. The reverse-biased...
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Nov 14, 2012
Blog Post:
Input Bias Current of CMOS and JFET Amplifiers
Bruce Trump
CMOS and JFET-input op amps are often selected for their low input bias current (I B ). But there is more to this than the single line in the spec table—subtleties that you should be aware of. Click Here to read on EDN web site. Index to all The Signal blogs.
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Nov 9, 2012
Blog Post:
Matchy Matchy—how alike are dual op amps?
Bruce Trump
Some circuits benefit when the characteristics of two more op amps are closely matched. So inside a dual or quad op package, how closely do their behaviors match? Hummm? The most common request on our precision amplifier E2E forum is for matching offset voltage and offset voltage temperature drift...
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Oct 30, 2012
Blog Post:
Controlling Volume—log pots
Bruce Trump
Have you ever tried to use a linear potentiometer (pot) as a volume control? Yikes! The volume jumps up much too rapidly. It requires a safe-cracker’s touch to adjust the volume to quiet listening levels. Thus the logarithmic potentiometer . Our senses have extremely wide dynamic ranges. Our...
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Oct 23, 2012
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