41

It will be one of two things & more than likely both: The probe you are using is not suitable, be it in frequency or in its compensation (the little screw on the side of the probe). A 10 MHz scope is too slow for a 4.5 MHz signal Here is the buildup of a squarewave up to the 100th harmonic (4.43 MHz fund): import numpy as np from matplotlib ...


32

You should realize that a 4.43 MHz square wave has a much larger bandwidth than 10 MHz. A "proper" 4.43 MHz square wave will contain frequencies up to and beyond 50 MHz. That is because a square wave is made up of a whole sum of frequencies (as opposed to a sinewave which is only one frequency, this is why EEs use it a lot). If you had an ideal 4.43 MHz ...


28

High speed with a small difference is difficult to get. Note that not only do comparators tend to have higher input offset voltages than opamps, but also much higher effective noise, as to get high speed they are wideband beasts. Oliver Collins produced a paper a couple of decades ago showing that you get much better results, that is less time jitter, if ...


25

They are not completely different. They are much more similar than you think. Technically, a comparator is just an op-amp optimized to operate in the saturation region (have the output saturate since it is always either LO or HI, but be able to leave saturation quickly for fast switching). Being linear in the linear region is not a design priority. An op-...


20

As a first approximation, there isn't a difference. A similar question might be "what's the difference between a DC motor and a generator?" Either will function in either capacity, but each is optimized to maximize certain qualities at the expense of others, according to the intended application. Let's compare the internal schematic for a common op-amp, ...


18

You have fallen into a classic XY problem1 trap. However, thanks for briefly mentioning the original issue, as that makes the overall situation easier to understand. You have a genuine problem ("X"): things are not working with the distance sensors. That is not enough detail to help you with the actual problem, but I'll come back to that. You are having ...


16

A retriggerable monostable multivibrator such as 74LV123 would meet your requirements well: Minimum pulse width 3.0 ns for 3 volt operation, 2.5 ns at 5 volts. Output pulse width configured by external R/C, typically 470 microseconds Retrigger time 45 ns (3 volts) to 40 ns (5 volts). It is a standard logic IC, very little complexity, and there are two ...


16

The datasheet link you provided was for the shorter summary datasheet. You need to look at the complete datasheet to get the comparator propagation delay. http://www.atmel.com/Images/Atmel-42734-8-bit-AVR-Microcontroller-ATmega48PA-88PA-168PA_datasheet.pdf On page 384 the analog comparator propagation delay (the time delay between a change in the ...


15

The circuit is a comparator and can be remarkably useful more or less as shown. I have used a circuit essentially the same as that in production equipment to meet a requirement which was difficult to meet easily and cheaply by other means. There are several ways to look at the circuit. The circuit does not care which way you look at it - but one or other ...


14

A comparator is often close to being a linear amplifier that is optimised to achieve rapid switching around the point where the voltage difference between two inputs are very close to zero. A comparator MAY include hysteresis which makes it less linear in action, but this is not an essential component. If you look at the block diagrams of the very old (...


13

Opamps are optimized for linear operation, in which the voltage difference between the input terminals is kept very small via feedback. As a consequence, the performance when using them in a nonlinear or open-loop application tends to be poor. In particular, charge storage on internal nodes tends to cause opamps to respond very slowly when coming out of an "...


13

This is a typical use of a conventional Operational Amplifier working as a Comparator. Lets's first describe it intuitively: If we left C1 out of the circuit (disconnected), we have an Op-Amp with no feedback (negative or positive). Under this condition, the output of the amplifier will be the difference of its inputs multiplied by the open loop gain. So, ...


13

Take a look at the basic schematics of the internals shown in the data sheets for the LM324 (regular op-amp) and LM393 (comparator) respectively: - The input stages are both pretty similar but the first big difference is the internal compensation capacitor inside the LM324 op-amp (shown with a red box around it). This compensation will ensure that with ...


13

I think Brian's non-SW answer is the best but here's a purely analogue solution. Use a circuit that inherently chooses the highest voltage input (from several) and puts that to the output. Ditto the circuit for the lowest voltage. Consider the precision rectifier: - It produces an output voltage that follows the input voltage throughout its positive range. ...


12

Yes you can. There are some applications notes using the differential pairs inside an FPGA as a low cost ADC. There is a very good document describing this that you can use for your design: Analysis on Digital Implementation of Sigma-Delta ADC with Passive Analog Components


12

You'll likely want to measure the total of many zero crossings (and divide by 'many' before taking the reciprocal).. or average many measurements.. otherwise noise in the signal will unduly affect your measurement, and you don't need the answer that quickly. You can measure easily to a couple hundred nanoseconds with a typical 8-bit micro (so 200ns in a ...


11

I think you can just use standard "precision rectifier" circuits. You need a dual opamp and diodes. To get the output down to zero volts, a negative supply is required.


11

The LM393 modules you see advertised on eBay aren't microphone amplifiers as such. They are advertised as sound detection modules, which deliver a (more or less) digital ouput. That module has an LM393 on it, and is advertised as a sound detector. It has an active low output, which matches the capabilties of the LM393 - the LM393 can only pull down. It ...


11

One window comparator, a 3 bit counter, and an 8:1 analog mux to connect one thermistor to the comparator. If all you need to know is that they are all fine; that's 3 chips, job done. (74HC163, 74HC4051, comparator, plus something like a 555 to clock it). As Andy says, the MUX (e.g. 74HC4051) has fairly low ON resistance, so each thermistor connects to one ...


11

The recommendations for you are very simple. Use a comparator for this application instead of an opamp. Select a newer part that operates with orders of magnitude faster response time. It would be the very best thing if the 741 could be eradicated from face of the earth. Here is what can be achieved with the venerable LM393 at 5kHz. The shown circuit will ...


10

Vref Since you use the same voltage for the resistor divider and Vref the ADC reading will be independent of that voltage: if your ADC reading is 123 at 3.3 V it will also be 123 at 3.0 V. So the absolute value of Vref is not really important. Nevertheless it's a good idea to have a Vref which is independent of other circuitry. In your schematic the 3.3 V ...


10

I've never seen a different symbol for comparators, so I had to make up this one: The hysteresis symbol refers to the hysteresis which is often built-in into the IC, or otherwise is almost always needed in the circuit. Does this make sense? edit Olin objects. He's right: it suggests a built-in hysteresis, rather than a required one. So second attempt:


10

Both op-amps and comparators are types of amplifiers. The triangle symbol is used for these and many other kinds of amplifiers. You will find that power amplifiers and digital NOT gates also have very similar symbols (but only one input pin each), for example.


9

As shown the circuit does not work [tm]. Overall, without intending to be rude, I'd say the circuit was "designed" by someone with a poor understanding of the task and also drawn incorrectly. BA10358 datasheet here - immensely detailed information but seems normal enough. 0.2 V/uS slew rate and 0.5 MHz "bandwidth". As shown, U1A inverting input is at 11 ...


9

You'll need an opamp that can swing up to vcc. Old things like the 358 cannot. It's an inherent limitation of the design. Look for rail to rail op amps, or better yet, use a proper comparator!


9

Those op-amps with very low offset (such as the TLC2652) have much too low a bandwidth for what you want (about 2 MHz) so, realistically you need to compare apples with apples. Also, not specified in that device's data sheet is how the input offset voltage changes with common-mode input voltage. For a comparator, large common-mode offsets are expected and ...


9

This is a classic misconception: "VBE is constant, BJT transistors are current-controlled devices." Nope, wrong. So, your #1 above is wrong. Long-tailed pairs are based on changes to VBE. The VBE becomes the transistor's voltage-input. In BJT transistors, the collector current is determined by the potential-barrier of the EB junction. (This is the ...


9

When selecting a comparator, it is always best to choose a part that is specifically designed for the job. Op amps can be used as comparators, but really, it is usually best to just buy a comparator! As for the 741 IC, this has many features that are undesirable for a comparator, as a lot of people will tell you. However, we can focus on your specific ...


9

The LM311 has an open-collector output. You need to connect the open emitter to ground, not VCC, and provide a pullup resistor on the open collector output. Don't try to use an LED as a flyback diode. Use a diode with a high surge current rating.


8

I'm not an expert on using op-amp or comparators but from my understanding, many op-amps can be used as comparators, the main difference is that the op-amp uses feedback to define the amplification value and the comparator doesn't care much about a linear output since usually we only need a high or low value from it but essentially they perform quite ...


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