• Knowing Where to Tap

    Jake, a respected veteran engineer in a power generation plant, retired with great congratulations and accolades. A few months later the plant suffered a major malfunction—a real meltdown with all systems involved. The engineering staff could not quickly diagnose the problem so with due urgency they called Jake for an emergency consultation.

    He surveyed the situation, checking the condition of some indicator lights…

  • Pop Quiz!

    Put away your books and take out a sheet of paper. Each question relates to one of The Signal blogs over the past 15 months. If you have difficulty answering, click on the link to bootstrap knowledge on the topic. Answers are at the end so you can score yourself. Have fun!

    1.   A gain of -0.1 (inverting) amplifier…

    • a)      is very likely to oscillate.
    • b)      requires an op amp with special stability criteria.
    • c)       will…
  • Settling Time

    Settling time is the time required for an op amp to respond to an input voltage step, enter and stay within specified error range of the final value. It’s important in applications that drive an a/d converter, digitizing rapidly changing inputs. But let’s look beyond the definition and focus on the character of settling waveforms.

    Last week’s blog on slew rate showed how an op amp transitions from a…

  • Slew Rate—the op amp speed limit

    Slewing behavior of op amps is often misunderstood. It’s a meaty topic so let’s sort it out.

       Click Here to read on EDN Magazine web site.

       60+ interesting The Signal topics.

  • Grounding Principles

    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 techniques. Wow. Big topic, but I may be able provide some insight with a couple of simple examples.

    Figure 1 shows inverting…

  • Handy Gadgets and Resistor Divider Calculations

    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 desktop computing caused their decline so you seldom see them today. I still use a variant of one—an old cardboard R-L-C…

  • Chopper Op Amps—are they really noisy?

    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.

  • Bypass Capacitors… yes, but why?

    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 ability to reject variations in the power supply voltage. Figure 1, an example, shows that this rejection capability…

  • Rail-to-Rail Inputs—what you should know!

    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 signal through the lower portion of the common-mode voltage range, to slightly below the negative rail (or single-supply…

  • Op Amps… G=1 stable & decompensated

    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.

  • Paralleling Op Amps—is it possible?

    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 point. Don’t use the simple circuit on the left. Directly paralleling inputs and output of two op amps is sure to start…

  • Resistor Puzzle Solution... and a rant on schematics

    Did you see last week’s resistor puzzle? Check it out if you missed it. Here’s the solution:

    We’re not accustomed to reading three-dimensional schematics so the first step is to redraw it clearly. There are three distinct paths from A to B, colored blue, green and red. Each has a series connection of 1Ω—R—1Ω.  The 3Ω resistors are effectively in parallel with the “R” resistors…

  • Resistor Puzzle—the sequel

    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 values are indicated, except for those marked “R?” in red.  What is the required value for R?


  • 1/f Noise—the flickering candle

    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… e2e.ti.com/.../4812.Flicker-Noise-v1.xlsx

    Note:  This file is different than the one posted a month ago.


  • Simulating Gain-Bandwidth—the generic op amp model

    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 sensitivity to GBW. Most SPICE-based circuit simulators have a simple op amp model that you can easily modify. TINA’s is…

  • ESD… Zapp!

    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 devices. It simulates nasty mistreatment that might occur during handling and assembly. Without internal ESD protection circuits…

  • Op Amp Noise—but what about the feedback?

    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 noise calculation file here…e2e.ti.com/.../8750.Non_2D00_Inverting-Amp-Noise-v2a.xlsx

        Other interesting “The Signal…

  • Comparators—what’s all the chatter?

    It’s an easy concept—the inputs compare two voltages. The output is high or low. So, why all the chatter through the transition?

    This effect usually occurs with slow changes through the transition voltage. Often it’s because the input signals have noise that jiggles through the transition voltage causing a chattering output. Even with very clean input voltages, comparators have their own noise—like an op…

  • Put Gain Up Front—waxing philosophical

    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 a modest first-stage gain of ten, the second stage could have a whopping ten-times the error or noise and it would contribute…

  • Input Capacitance—common-mode?...differential?… huh?

    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 input. The feedback network reacts with input capacitance to create an unwanted pole. Scaling the impedance of the feedback network…

  • Op Amp Noise—the non-inverting amplifier

    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 “The Signal” Topics.

  • Brain Teaser—the solution

    Did you miss last week’s brain-teaser? Go back if you’d like to test your skills before seeing the answer below.

    Repeating the question… what is the resistance of this infinite resistor network?

    Though this can be solved numerically (and very accurately) there is a closed-form solution and I challenged readers to submit an answer with an explanation. The key is in realizing that second resistor…

  • Holiday Brain Teaser

    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:  Write a clear, concise, explanation of how you solved it, including the math and I will publish it next week. The best…

  • Breadboarding with Micro-Packages—Ouch!

    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 kit eases the pain. For ten bucks you can mount SO-8, SOT23 (3, 5, 6, or 8-lead) MSOP-8, SC70-6, SOT563-6 packages. We won…

  • PCB Layout Tricks—striped capacitors and more

    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 foil of the spiral wrapped innards. I’m finding that few engineers these days know this, and proper orientation can make a difference…