# Tag Info

## Hot answers tagged pulse

27

You've changed the requirements by a lot! Measuring something in nanoseconds is hard. Measuring something with a +-100 ns accuracy really isn't. A 10 MHz counter works perfectly fine for that, do 20 MHz if you want to be sure. Any modern 32 bit microcontroller (read: 2€ investment...) has timer/capture units that can do that for you. You've went from a ...

15

Q2 is a ramp retrace generator. Q1 is a reset comparator when it’s Vbe >200 mV for Germanium. But if Q2-C is low, and Q1-E is high , Q1 is defective due Q1 Vbe defect. Now I see Q2 & Q4 Vbe >1V are both defective Theory of Op. This is a clever little 2 transistor Astable multivibrator with a pulse generator to drive the speaker with a spike from 1/...

15

This circuit was copied out of the RCA Hobby Circuits Manual 1968. Complete entry shown below, including original description of operation.

14

Luxury option: Time to digital converter chip, available from several manufacturers. Accuracy: picoseconds. AS6500 TDC7200 Easy option: Microcontroller timer in capture mode to measure pulse width, or time between two pulses. Pretty much any microcontroller will do the job, but accuracy will be at best one clock cycle, so you must choose a microcontroller ...

9

As others have said, a Schmitt trigger will clean it up. Reducing the 51k resistor to 10k or so may help as well. Also consider this waveform distortion is irrelevant for the typical intended electronic music function of the IC. A perfect 18kHz square wave is barely audible under good conditions. The harmonics of the imperfect square are way above audible ...

9

Your cheapest solution is going to be determined by the cost of your time , components and circuit board with debug time. In this case your best solution is a used 100 MHz counter off EBAY for \$150 https://www.ebay.ca/itm/AGILENT-HP-5316B-HIGH-PERFORMANCE-FREQUENCY-COUNTER-100-MHz-LOOK-REF-330G/193032320482?hash=item2cf19f75e2:g:O8UAAOSws3ldSDHf

9

(basically +/- 100ns). Well then, a cheap 8-bit microncontroller like ATTINY2313 can be clocked at 20Mhz, then you can just use its timers in input capture mode and that will get you +/- 25ns precision at each end of the pulse for over-all +/- 50ns precision (modulo clock jitter and innacuracy so use a good crystal for the clock) 75ns accuracy should be ...

9

To answer the question you didn't ask: In normal operation, with the transistor on, the base-emitter voltage of a bipolar junction transistor is about one diode drop. That's 0.7V for a small-signal silicon transistor (it can be more if the thing's carrying huge currents), and about 0.3V for a small-signal germanium transistor. The direction of the voltage ...

7

I think the most realistic approach here is probably still a bit tricky: First of all, you'll have to realize that your signal has a pretty high bandwidth, assuming that the rise time of your pulses needs to be pretty steep to even get the required timing accuracy (e.g. if your rise time is 40 ns, then in 1 ns of an edge not that much voltage difference ...

5

If I were going to design such a circuit, I would borrow techniques from the traditional transistor multivibrator. simulate this circuit – Schematic created using CircuitLab If you run the simulation, you'll see that it produces one output pulse for every six input pulses. The lockout period is just over 500 ms. Adjust C1 and R4 to control the output ...

5

Unfortunately this isn't really a mechanical problem and has little to do with the relay itself. A mercury-wetted relay is certainly the right choice, but their contact closure speeds are a couple orders of magnitude faster than the rise times you're seeing. They typically achieve contact closure times of 3-5 picoseconds, and the contact break time (at least,...

5

Just add another component: Pick any monostable multivibrator that can generate a pulse with the desired timing characteristics; pick any (slow) two-channel DAC to generate the two desired, constant output voltages (if one output voltage is always GND, you need only one channel); use an analog multiplexer (random example: TS12A12511) to switch the output ...

5

It's an evaluation board for the chip, so they will often add footprints to allow the engineer to experiment with component values. If you look at evaluation boards, quite often there is space for extra decoupling caps, resistors, etc. The purpose of an evaluation board is not just to watch the chip work, but to experiment on it and try stuff. In this case, ...

4

This is a perfect use case for a microcontroller, DAC, and a voltage controlled amplifier. With minimal load, an AB audio amp and SPI or on-die dac I estimate your system will hit the 1 us single shot requirement with appropriate firmware on an 8 bit MCU.

4

If you look at the populated PCB, you can see what options these 0Ω resistors offer. The resistors R31 and R33 are not populated and are shorted out. But R18 is populated with a 1.1Ω resistor. This is an evaluation board which allows the user to experiment with the components. In this case the developers determined a 1.1Ω resistor was required. The ...

4

A few observations: - Have you considered worst case or typical leakage currents from the analogue switch? With 6 nA leakage current (worst case) through 200 kΩ there will be an error voltage of 1.2 mV at the input of U1 and that, on the highest gain configuration will mean an offset error voltage of about 108 mV on U1's output and three times this on U4's ...

4

Counting pulses with 1ns precision is a tall order. That rate rules out all the commonly used logic families like 74XX, CD4XXX, etc. Even the "high speed" varieties are nowhere near fast enough. That leaves you with ECL (Emitter Coupled Logic) as the next step up. These are fairly expensive and use a lot of power but when that's what you need, ...

4

Since you imply that 10 ns resolution is acceptable, a 50 OR 100 MHz timer can be built with either 10K or 100K ECL, or Schottky TTL (74Sxx or 74ASxx). You will need an accurate 50-100 MHz oscillator to clock the counters, and this is not a simple thing to design. Note that at your frequencies, the display will be updating far more rapidly that the eye can ...

4

It does work like an SCR as you described. Assume C3 is charged to a higher voltage than the junction of R1 and R2 (about 4V). C3 discharges through R5 and RV1 relatively slowly creating an exponential negative going ramp until the voltage becomes slightly lower than 4V; Q2 will then start conducting. The current from Q2 through R6 will forward bias Q1 that ...

3

Do as much as possible in the FPGA that you already have: Since there is a 100MHz clock, the period is 10ns. The minimum counter division is 5, which is easy, getting to 50ns. The maximum counter division for your stated 25ms is 2,500,000. $$\text{ceil} \left( \log_2 \frac {25\text{ms}} {10\text{ns}} \right) = 22$$ You need a minimum 22-bit counter in your ...

3

is a high voltage MOSFET appropriate for this application, keeping the requirement of low leakage current and fast switching in mind? Is there a better component? (I have purchased a Vishay IRFPG50 (1000v, 6.1A)) The types of components that are appropriate depend on what you need your switching to look like. If you just need to turn on quickly and drain ...

3

If your concerned about parasitics then put them in the model. Simulate the worst case parasitics. A 12mil 1 inch trace has 35mΩ's of resistance and roughly ~12nH and 1.5pF. Connectors can have resistances in the 100mΩ's range. Most of the traces between components will be much shorter than this, but put in a 35mΩ resistor between various components and ...

3

One simple approach would be to have a free-running counter that measures time in units of its clock period. Each channel, when it receives a pulse, captures the value of the counter into a register. The counter must be big enough so that it doesn't overflow in the expected total time between the first and last pulses. Once all of the channels have triggered,...

3

Apply the pulse signal through a capacitor and a diode half bridge to the gate of a mosfet. This will turn the mosfet on as long as the pulses are coming. The mosfet will be off when the pulse train stops (hi or low doesn't matter) The pulse voltage has to be large enough compared to the gate threshold of the mosfet. The 2N7002 has about 2.5V threshold ...

2

The voltage rating of the chosen capacitor just needs to be greater than whatever logic voltage you are working at (e.g. 5 volt). Using a 100V capacitor in a low voltage circuit won’t do any harm.

2

If you had a scope you could also see whether the spikes are the kind where a schmitt trigger would help more. But more likely, is to debounce and/or blank your pulses. Debounce: Only accept a pulse after it has been stable for long enough. After a transition is detected, take two or three samples over some time interval and only count the pulse if it's ...

2

If you just need the pulse, you could do something like this. Add an inverter if needed. simulate this circuit – Schematic created using CircuitLab The output can be tuned by adjusting the RC values R1, R2, C1.

2

I'd definitely not bother too much on analog filtering. 24 bits is such resolution that you get some 20 uV resolution even on the plain full input spectrum. Mains network own noise is far above that even in the 1 kHz- 10 kHz band of interest due the heap of switch mode power supplies and lamp drivers connected. (Reserch gate https://www.researchgate.net/...

2

In TDR, the two main parameters are pulse length (or rather shortness), to get bandwidth, and pulse power, to get signal to noise ratio. Once you've struggled to produce those, the pulse shape is whatever the mechanism you've used happens to give you. It's rather like the dog that says 'sausages'. The wonder is that the dog can talk at all, not that its ...

2

You want to drive a capacitive transducer at 3.5MHz with 120Vp-p, which is a fairly tall order. The peak power is rather high (3A peak at 60V). You can purchase high-voltage power op-amps, some of which have example circuits that show driving heavily capacitive loads. I've done a discrete booster amplifier for driving piezos, but it's tricky to get it to ...

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