14
votes
Accepted
Cutoff frequency of RLC band pass and band stop filter
RLC Passband and Stopband
Your question doesn't explicitly take note of the fact that there are four distinct RLC filters that are either band-pass or band-stop. But I'd like to list them for those ...
- 77.4k
9
votes
Completely different circuit response with 1000kΩ than with 1MΩ resistance
In PSpice m and M are thousandths. You need to use Meg.
- 13.8k
8
votes
Why is superheterodyning better than direct conversion?
There are quite a few advantages.
Taking a look at a typical superhet (up to the IF):
The input signal at the RF input is small (as low as -122dBm in some narrow band voice systems I have worked on -...
- 22.1k
8
votes
Two bandpass filters in series, why use different voltage dividers?
It looks like a case of (roughly) wanting to balance the resistance seen by each input of the two op-amps in order to minimize errors due to the input bias current. However, they have not done this ...
- 128k
7
votes
Accepted
Detect an IR signal with a photodiode to use it with a microcontroller
Read the following data sheet extract from the TL074 and see why your circuit is ineffective: -
So, if you fixed the supply rails the next problem will be that your output signal will be negative ...
- 443k
7
votes
Accepted
Is the resonance frequency actually at the center of the passband of a bandpass filter?
I remember learning in Circuit Theory that the resonance frequency of a series RLC circuit is the geometric mean (or geometric middle) of the half-power (cutoff) frequencies:
I hope this helps.
- 1,006
6
votes
Accepted
Analysing a band pass sallen key filter
You can use modified nodal analysis to solve for all unknown node voltages and unknown currents.
Once you get the node voltage, you can find the transfer function.
For the analysis, I denote node and ...
- 1,537
6
votes
Why is superheterodyning better than direct conversion?
Note that this answer is skewed toward analog radio reception. The rules are different for software-defined radios, and for digital services.
The biggest drawback to direct conversion is sideband ...
- 45.4k
6
votes
How to properly design LC bandpass filters?
You have given enough parameters to design the required filter:
source termination 50 ohms
load termination 50 ohms
bandwidth 200 kHz
center frequency 1.81 Mhz
Any number of "applets" can ...
- 24.3k
6
votes
Accepted
Meaning of 'Bessel Filter'
A Bessel filter is only specified as a lowpass, not anything else, and the characteristic is that it tries to approximate an ideal delay, \$\mathrm{e}^{-st}\$. Given the nature of the Bessel ...
- 21.2k
5
votes
Accepted
"Top coupling" in VHF bandpass filter
That filters has 4 sections, which if we number them 0 to 3 ...
0 is coupled to 1 by mixed coupling which is mostly inductive
1 is coupled to 2 by capacitive coupling through Cc
2 is coupled to 3 as ...
- 162k
5
votes
Accepted
Picking the right opamp
This specific application
Presumably you want to power the op amps with the (single) 5 V DC supply, so your main requirements are:
an op amp that can operate with a 5 V supply or less
an op amp which ...
Null♦
- 7,588
5
votes
Designing a circuit from a transfer function
Your transfer function can be obtained in different ways and one of them could be by cascading two stages with a buffer in-between. Your original expression follows the form
\$H(s)=H_0\frac{1+\frac{s}...
- 20.9k
5
votes
Accepted
Digitally selectable filter
It would be better to have 560 ohms to ground, and use only one transistor, switching a value of 3k (should be 2.9k) to ground. That way most of the current flows in a real resistor, which minimises ...
- 162k
5
votes
Are these two circuits the same?
These two circuits can provide similar bandpass frequency response.
However, the lower-frequency cutoff must be considerably lower than the high-frequency cutoff. This means that the frequency span ...
- 24.3k
5
votes
Why is superheterodyning better than direct conversion?
Yes, direct-conversion receivers exist, but they require special care, especially with certain kinds of modulation.
For example, with SSB modulation, in order to reject the unwanted sideband, your ...
- 170k
5
votes
Why is superheterodyning better than direct conversion?
Direct conversion is conceptually simple, but requires considerable engineering to do it right. Besides Dave's & Tim's answers, there is a subtle pernicious potential problem with direct ...
- 24.3k
5
votes
Building a band-pass filter using an op-amp
The maximum output amplitude of an op-amp, above a certain frequency, decreases with frequency. From the LT1128 datasheet we have this graph
What this graph tells us is that even though a particular ...
- 20.7k
5
votes
RLC band-pass filter
Your simulation is only running between 100 KHz and 10 MHz.
Try editing the command to:
.ac dec 1000 10 100K
- 3,401
4
votes
How could I design a circuit for a solar panel so that it only produces output from a red laser?
Firstly, "laser" tag doesn't (usually) use lasers - and for good reason:
Lasers are dangerous and can blind people. Use with caution.
Laser tag normally operates using a focused infra-red beam. ...
- 56.1k
4
votes
Discrete high order filter (passive?)
Well, not completely passive. But not what's usually meant when one uses the words 'active filter'.
You can't be "a little pregnant". A filter also can't be "not quite passive, but also not active": ...
- 90.3k
4
votes
Accepted
Sallen-key second order bandpass filter low frequency response
A square wave of 200 Hz contains odd harmonics all the way to infinity. The 25th harmonic of 200 Hz is 5 kHz hence you see the band pass filter extracting this harmonic and greatly amplifying it.
...
- 443k
4
votes
Designing a multi-stage BJT amplifier
Your design is a very basic and might work but since it has no feedback it is not so predictable in how it will behave in practice.
The "proper" engineer's way of designing this is by use of feedback....
- 80.4k
4
votes
Completely different circuit response with 1000kΩ than with 1MΩ resistance
Not sure what kind of simulator that is, but a common pitfall is:
1M = 1 milli (Ohm, Volt, Ampere) and 1Meg = 1 Mega (Ohm, Volt, Ampere).
Because they don't care about capitalization they can't make ...
- 17.5k
4
votes
Transfer function of a bandpass
These answers are obviously correct but they represent the brute-force approach. Nothing wrong here but considering all these lines, it is likely that mistakes or typos get in the way of the correct ...
- 20.9k
4
votes
Accepted
Is it possible to design a compact antenna for detecting the presence of 50 Hz mains voltage at very short range?
The classic circuit for non-contact voltage detection is just a high-impedance amplifier with some kind of signal conditioning (if necessary) to turn the AC into a sustained signal (eg. for a buzzer).
...
- 383k
3
votes
Accepted
LCR circuit with squarewave input: Why does the output take a decreasing amplitude through each cycle?
Your LCR resonator has losses, so it is a decaying sinusoid wave at 5 MHz.
Before it decays to zero, it is re-excited by the negative-going edge of your 1 MHz square wave. Then re-excited by the next ...
- 24.3k
3
votes
Accepted
Why is center frequency of a bandpass filter is given by the geometric average of the two cutoff frequencies?
Why is the center frequency of a band-pass filter is given by the geometric average of the two cutoff frequencies instead of arithmetic average?
Because its the ratios that are relevant, not the ...
- 312k
3
votes
Accepted
Twin-T filter decay rate (drum circuit)
After some experimentation I finally solved the riddle: It was noise affecting the feedback loop. After shrinking the feedback resistors by a factor of ten and increasing the capacitors by the same ...
- 61
3
votes
Impedance calculation
Perhaps the easiest way to determine this without using any math is to simulate it in a program such as LTSpice. If you aren't familiar with this tool, I strongly encourage you to look into how to use ...
- 335
Only top scored, non community-wiki answers of a minimum length are eligible