Rarely Asked Questions...
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The column, "Rarely Asked Questions: Strange but true stories from the call logs of Analog Devices," is published monthly in EDN and Design News. Technological troubleshooting, insight and ideas from the experts at Analog Devices to help solve your real-world application challenges.
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Questions & Answers
and the strange but true stories behind them
| Issue 46: | What shall we do with an unused op-amp? |
The Question: In the RAQ on op-amps as comparators you mentioned an unused op-amp in a quad as being possible justification for using it as a comparator. What do you do if you've an unused op-amp and don't need a comparator? Download this article [pdf, 129,560 bytes] |
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| Issue 45: | Glass Diodes May See the Light – and Hum |
The Question: A few months ago you discussed how to prevent the inherent high frequency (HF) noise of a switching supply from escaping into sensitive analog circuits and corrupting them. My op-amp output hums and no amount of supply filtering helps. What should I do? Download this article [pdf, 127,971 bytes] |
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| Issue 44: | Keeping Common Modes Common |
The Question: How come my A/D converter is not able to achieve full scale as the datasheet specifies? Download this article [pdf, 95,957 bytes] |
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| Issue 43: | Impedance Measuring Chip Offers
Little Resistance to Applications |
The Question: I came across your Impedance measuring chip (IMC) in a recent article. It sounds interesting, but how does it work and what can it be used for? Download this article [pdf, 125,661 bytes] |
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| Issue 42: | Are Your Filters Filtering? |
The Question: Why is my A/D converter's anti-aliasing filter showing inadequate spurious and noise rejection? Download this article [pdf, 731,084 bytes] |
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| Issue 41: | What's in Your Toolbox? |
The Question: Do you prefer power tools or hand tools for solving problems? Download this article [pdf, 103,363 bytes] |
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| Issue 40: | How Big Is It? |
The Question: How can I handle signals with huge variations in amplitude? Download this article [pdf, 102,537 bytes] |
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| Issue 39: | Off-amps, what the heck are off-amps? Op amps with no power applied, of course. |
The Question: What kind of performance (pick a parameter, it could be input impedance or any other op amp specification) can I expect from your amplifier ... when the power is off? Download this article [pdf, 126,118 bytes] |
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| Issue 38: | Single Supply Amplifiers – They Sound Simple ... are they? |
The Question: Running rail-to-rail op amps on a single supply sounds like a winning combination, but what drawbacks will I encounter when using amplifiers like this? Download this article [pdf, 119,519 bytes] |
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| Issue 37: | Lock Down That Noise - Don't Let It Escape |
The Question: How can I prevent switching-mode power supply noise from devastating my circuit performance? Download this article [pdf, 1,056,768 bytes] |
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| Issue 36: | The Difference Between Different Differential Amplifiers |
The Question: I'm perplexed. Why is the output voltage of my ADC differential amplifier driver not what it should be? Download this article [pdf, 737,280 bytes] |
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| Issue 35: | Stress Is Bad For You – and For Analog ICs
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The Question: Does too much mechanical stress when mounting precision analog ICs damage their accuracy? Download this article [pdf, 126,976 bytes] |
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| Issue 34: | A Capaciticectomy? Sounds Awfully Painful! |
The Question: One of your high-speed triple amplifiers is oscillating. What's wrong with it? Download this article [pdf, 118,784 bytes] |
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| Issue 33: | Hysteresis Blocks Magic |
The Question: Can I recalibrate my precision analog circuits to achieve higher accuracy? Download this article [pdf, 118,784 bytes] |
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| Issue 32: | Political Correctness and Datasheets |
The Question: Datasheet Specifications: Provoking or Confusing? Download this article [pdf, 114,688 bytes] |
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| Issue 31: | Too Hot or Too Cold May Be Just Right |
The Question: Are absolute maximum and minimum temperatures as absolute as voltage or current ratings? Download this article [pdf, 995,328 bytes] |
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| Issue 30: | CAPACITIVE SENSORS: Rugged Enough for the Real World? |
The Question: I've seen cap sensors used in consumer electronics, but are they rugged enough to function in a harsh industrial environment? Download this article [pdf, 688,128 byte] |
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| Issue 29: | Half Full or Half Empty? Thoughts on Capacity. |
The Question: Are all components with just two wires as complicated as the resistors we discussed recently? Download this article [pdf, 114,688 bytes] |
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| Issue 28: | What's Your Amplifier's Febricity Due to Electricity? |
The Question: What's the best way to measure the die temperature of a small package op amp or similar device? Download this article [pdf, 565,248 bytes] |
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| Issue 27: |
Resistors (and old ladies) have hidden depths |
The Question: You recently discussed the thermal noise of resistors. They seem to be such straightforward components with just two connections and one simple property: resistance. Do they have more traps for the unwary? Download this article [pdf, 770,048 bytes] |
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| Issue 26: |
Op-Amp Noise can be Deafening Too
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The Question: Last month you blamed op amp noise on external resistors. Surely this is not always the case? Download this article [pdf, 106,496 bytes] |
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| Issue 25: |
Resistor Noise can be Deafening, and Hard to Reduce |
The Question: My low-noise amplifier is not low noise enough. What am I doing wrong? Download this article [pdf, 167,936 bytes] |
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| Issue 24: |
Are leaky amps sinking your design?
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The Question: My amplifier "leaks" a low level signal at the output with the power supplies off. What gives...is my circuit sunk? Download this article [pdf, 602,112 bytes] |
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| Issue 23: |
Should you butcher your circuit or your test gear? Capable engineers should be prepared to question, and modify, anything, not just their own designs. |
The Question: While probing a new high-speed amplifier board, I noticed the output had huge overshoot and was ringing like a bell. I had paid close attention to the layout, optimizing supply bypassing, grounding, parasitic reactances, and trace terminations. Where did I go wrong? Download this article [pdf, 71,688 bytes] |
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| Issue 22: |
Things (animals and ADCs) are not always what they seem
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The Question: Must I consider high frequency issues when driving a slow ADC? Download this article [pdf, 65,536 bytes] |
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| Issue 21: |
Breadboarding With Surface Mount ICs Too small, or not too small? That is the question...
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The Question: How do I build breadboards with tiny surface mount (SM) ICs? Download this article [pdf, 90,112 bytes] |
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| Issue 20: |
Igor, pass me some supply sequencers!
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The Question: Last month you said that some absolute maximum ratings depended on the value on some other pin of an integrated circuit (IC). How do I ensure that they are not exceeded during power-up? Download this article [pdf, 94,208 bytes] |
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| Issue 19: |
Observing Maximum Ratings or How to Avoid Forecasts of Doom
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The Question: How much safety margin is there in "absolute maximum" ratings? Download this article [pdf, 782,336 bytes] |
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| Issue 18: |
Just How Accurate was William Tell, Anyway?
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The Question: How accurate is an ADC? Download this article [pdf, 1,036,288 bytes] |
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| Issue 17: |
More Chips are Better than One (or the Benefits of Belgian Food)
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The Question: When are two chips better than one? Download this article [pdf, 1,314,816 bytes] |
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| Issue 16: |
Replacing Optocouplers with Digital Isolators (or How a Midnight Ride Could Have Been Avoided)
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The Question: Can transformer-based isolators replace optocouplers? Won't there be problems with dc signals, magnetic fields and size? Download this article [pdf, 368,640 bytes] |
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| Issue 15: |
The Long Term Stability of Precision Analog ICs, or How to Age Gracefully and Avoid Sudden Death
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The Question: The life expectancy of my product is 20 years. How well will its calibration survive? Download this article [pdf, 163,840 bytes] |
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| Issue 14: |
Resourcefulness, or Why Good Engineers (and Good Cooks) Use the Best Available Components.
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The Question: Which (amplifier/switch/converter) is best in a (mobile phone/strain gauge/medical ultrasound system)? Download this article [pdf, 147,456 bytes] |
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| Issue 13: | It May be Greek to You, but Sigma Delta Converters are Not Really Hard to Understand
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The Question: Can you please explain, simply, as to a Bear of Little Brain, how sigma-delta converters work? Download this article [pdf, 110,592 bytes] |
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| Issue 12: | How Not to Design Active Filters (or Not Only Sharks Distract Divers) |
The Question: Why does my carefully designed active filter not meet its specifications? Download this article [pdf, 106,496 bytes] |
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| Issue 11: |
Comparators & Op Amps – May They Never Meet (or Good Advice from Mr. Punch) |
The Question: Why buy an expensive comparator when an op amp is just as good? Download this article [pdf, 364,544 bytes] |
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| Issue 10: | Digital Processing Does Not Always Rule (or What Makes an Analog Engineer Laugh?)
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The Question: Why recommend analog signal processing when digital systems are so cheap and powerful? Download this article [pdf, 28,672 bytes] |
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| Issue 9: | Grounding Converters (or Philosophy to the Rescue!)
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The Question: I can't believe that you recently advised us to connect the digital ground pin of ADCs to the system analog ground. Was this a mistake? Download this article [pdf, 32,768 bytes] |
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| Issue 8: | Happy Groundhog Day!
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The Question: Why do I have an output when my analog input is grounded? Download this article [pdf, 1,787,527 bytes] |
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| Issue 7: | It's Easy to Drive An EE to Drink – but What
Drives One to Poetry? |
The Question: My SPICE simulation worked perfectly, but now I've a large production batch which doesn't meet its specification. Download this article [pdf, 94,208 bytes] |
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| Issue 6: | Tick-Tock, Tick-Tock |
The Question: My clock is accurate to 1 ppm – what could possibly need improvement? Download this article (pdf, 852,045 bytes) |
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| Issue 5: | Check the Bias Current (or How to Ensure that a Blessing is Heard) |
The Question: The bias current in modern amplifiers is very small. Do I need to bother about it? Download this article (pdf, 1,571,506 bytes) |
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| Issue 4: | Caveat Emptor |
The Question: How do I make sense out of a data sheet ? Download this article (pdf, 126,976 bytes) |
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| Issue 3: | Isolating the Key Detail (or Lunching With a Mermaid and Pickled Herring) |
The Question: There is a fault in my CMOS multiplexer...? Download this article (pdf, 1,892,352 bytes) |
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| Issue 2: | Slow "Starting" ADCs (or the Beneficial Effects of Spirits in Diagnosing Converter Problems) |
The Question: To save power, my ADC is powered up only to make a measurement. The system is very accurate in continuous operation, but completely unpredictable when power is strobed. Download this article (pdf, 28,672 bytes) |
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| Issue 1: | Radio Frequency Interference (or How to Get a Free Lunch at a Very Good Restaurant) |
The Question: I've heard that RF can make low-frequency circuits do strange things. What's that all about? Download this article (pdf, 73,728 bytes) |
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