# Tag Info

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 ...
• 78.4k

### Completely different circuit response with 1000kΩ than with 1MΩ resistance

In PSpice m and M are thousandths. You need to use Meg.
• 13.8k

### 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 -...
• 22.5k

### 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 ...
• 132k
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 ...
• 465k
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.
• 1,046
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 ...
• 1,649

### 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 ...
• 46.7k

### 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 ...
• 26.8k
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 ...
• 21.6k

### Discrepancy between calculated and simulated cutoff frequencies of a bandpass filter

The circuit you show is a second-order bandpass filter. You cannot apply the classical design expressions pertaining to single-stage $CR$ or $RC$ filters, it is a common error. The reason is that ...
• 22.8k
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 ...
• 7,633
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 ...
• 169k

### 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}...
• 22.8k
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 ...
• 169k

### 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 ...
• 26.8k

### 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 ...
• 175k

### 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 ...
• 26.8k

### 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 ...
• 25.4k

### 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
• 3,532

### In a bandpass filter, when a square wave is applied into the input, why is the output a sine wave?

A good square wave will be composed of many harmonics at increasing multiples and decreasing amplitudes of the fundamental frequency. As you start to "filter" out the upper harmonics you ...
• 10.5k

### 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. ...
• 56.3k
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. ...
• 465k
Accepted

### 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....
• 81.1k

### 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": ...
• 97.3k

### 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 ...
• 17.8k

### 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 ...
• 22.8k
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). ...
• 409k
Accepted

### Why is my band pass filter giving a gain of 0.5 in the -3 dB gain region?

The good thing is that you have tried to make the two sections of filter not interact with each other by using impedances that are 100 times bigger for the second stage compared to the first stage. ...
• 465k