# Tag Info

## Hot answers tagged oscillator

### What is ground in a physical circuit?

Ground is what you define as the 0V point of a circuit. So you simply have a +9V supply in reference to 0V GND and a -9V supply in referenve to 0V GND. The total supply is two 9V batteries or 18V. For ...
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### What is ground in a physical circuit?

"Ground" mainly is an abstract concept. It is the voltage node you use as a reference point for all other voltages in the circuit. Because when we say this point/trace/pin is charged to ...
• 9,669
Accepted

### Why my RC-oscillator design does not produce any output?

first thoughts The RC phase shift oscillator is often studied in a somewhat more ideal circumstance; usually using an opamp to make things a bit more idealized. Using a single bipolar transistor as ...
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### How does this delay circuit work?

The circuit you show is called a relaxation oscillator. It's also called an astable multivibrator, which is essentially a flip-flop with phase-shifted feedback to make it oscillate. The capacitor is ...
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### PUT relaxation oscillator problems

The circuit shown above should work without issues, and flash the LED every few seconds. There is not really much to go wrong in these circuits if you keep the divider resistance down relative to the ...
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### Unexpected Behavior in Transistor-Coupled Astable Multivibrator Output

Not surprising the bottom circuit works in simulation, but you will blow the transistor in a real circuit since there is nothing to limit the base current. You likely need more base drive for Q3, but ...
Accepted

### Unexpected Behavior in Transistor-Coupled Astable Multivibrator Output

You are probably not switching enough current for the motor to work. Note that in your second schematic there’s no base resistor, while in your first circuit it’s 10k. The collector current will be ...
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### What is ground in a physical circuit?

In the physical context, all the ground symbols represent the same node. Every node which is connected to ground, using the same triangle symbol , is physically connected to every other node with that ...
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### How would this circuit work with a directly heated cathode?

Addressing OP's comment on another answer, Why would a choke/resistor be needed on the B+ line(apart from plate short)? Doesn't a choke basically act like a filter for HF noise? Principles used: AC ...
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### Are these filters suitable for this application?

Are those listed filters suitable for the task? And wich one of them is better? The best solution would be to use a passive 3rd order filter as shown in the datasheet. An active filter is unnecessary ...
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Accepted

### Does PLL stabilize the frequency variations of a crystal oscillator?

If you draw a block diagram of a typical PLL, the answer becomes obvious. The frequency divider is inserted in the feedback path. PLL from Wikipedia The output frequency will always eventually follow ...
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Accepted

### How would this circuit work with a directly heated cathode?

Yes your oscillator should work. Your little battery valves will have less transconductance so if it does not start reliably then increase the feedback and don't forget to place a choke in the B+ line ...
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### Tuned Gain Stage

That is the correct gain, at resonance, for the small-signal and low-frequency transistor model. The small signal model uses the general transistor model, linearized around the operating point. You ...
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### Unexpected Behavior in Transistor-Coupled Astable Multivibrator Output

Put a resistor in series with the base pin of Q3. This resistor value must be at least 5 times that of R4. Without this resistor, the voltage at Q2 collect pin is restricted, which will affect the ...
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### What is ground in a physical circuit?

The terminology commonly used in electronics is a bit unfortunate* because (at least in my opinion) it makes this concept harder that it needs to be. An alternative term for "ground" is &...
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### What type of crystal oscillator is this?

It should. No it does not load the crystal, it drives it. That's a common oscillator circuit. Many crystal manufacturer calls it the series resonant oscillator. The reason it may look funny is that ...
• 160k

### Frequency of Oscillators

One thing that stood out to me is that the frequency was usually controlled by an inductor and a capacitor, with a mathematical relation of the form, 1/LC No, that doesn't have the dimensions for ...
• 169k
1 vote

### Voltage-controlled oscillator problem

What do I miss here? What you miss are the subtle details. The frequency does vary between your two posted plots, but maybe not as much as you anticipated. The first plot (R14=80 ohm, R15=10 ohm) has ...
• 1,446
1 vote

### Voltage-controlled oscillator problem

I set the control voltage with the R14/R15 voltage divider, but for some reason the frequency does not seem to depend on the control voltage. Your simulation does not vary the control voltage, so you ...
• 5,640
1 vote

### Unexpected Behavior in Transistor-Coupled Astable Multivibrator Output

The base of Q3 cannot rise above +0.7V, due to its base-emitter junction. That junction behaves like a diode. To allow Q3's base to rise above 0.7V, which would be required if you wish the circuit to ...
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1 vote

### How would this circuit work with a directly heated cathode?

The original 1927 patent from Edwin Colpitts himself shows a vacuum tube oscillator with a directly heated cathode. The component symbols are different from our modern ones, but I don't think it's ...
• 409k
1 vote

### Calculating capacitor charging and discharge time using LM311 as Schmitt trigger astable multivibrator

I calculate the threshold voltages at 1.45V and 2.14V using an output voltage of 0.17V (low) and 5V (high), taking into account the 1K pullup (but not the 10k to the capacitor). Simulated values are 1....
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1 vote

### Calculating capacitor charging and discharge time using LM311 as Schmitt trigger astable multivibrator

First, we need to find the threshold voltage. If we assume that LM311 is LOW (0V) then the voltage at V+ will be equal to:  V_{TL} = V_{CC} * \frac{R_2||R_4}{R_1 + R_2||R_4} = 5V * \frac{7.96k\Omega}...
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1 vote

### Does PLL stabilize the frequency variations of a crystal oscillator?

With a digital PLL multiplying your reference, the MCU clock will always be N times your reference. If the reference changes 1%, the MCU clock will change 1%. 100 ppm (0.01%) variation is trivial and ...
• 169k
1 vote

### Does PLL stabilize the frequency variations of a crystal oscillator?

A PLL multiplies the running average of the input frequency over past cycles. A running average is a low pass filter, so it essentially low pass filters the rate of change of the input from the ...
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1 vote

### Does PLL stabilize the frequency variations of a crystal oscillator?

A slow time constant in the PLL can filter phase noise and make the clock more stable for short time periods. But the crystal will be responsible for the long time drift (long in terms of longer that ...
• 9,669
1 vote

### Why my RC-oscillator design does not produce any output?

If you want all three RC stages to have the same corner frequency, some modification is in order. The aim seems to be an RC product of $1k\times 100n$. You'd like R1 to be lower (ideally zero from ...
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1 vote

### How does a capacitor in an astable multivibrator turn off a BJT?

Introduction I am thrilled to answer this question, as it brings back fond memories from my high school days in the 60s. It was one of the first circuits I built, using PNP transistors and lamps in ...
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1 vote

### How does a capacitor in an astable multivibrator turn off a BJT?

Late answer, but consider this: Both inductors and capacitors store energy, and there always is a time element to their charging and discharging. It's the "dt" in the equations. Because of ...
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1 vote

### Why will an ideal double integrator oscillator only oscillate at one frequency?

As discussed in the other answer, stability criterion, and practical effects (nonideal integrators), are important to consider. I'll just run through a simple calculation that should prove ...
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