# Questions tagged [low-pass]

A low-pass filter lets lower frequencies through and blocks or reduces higher frequencies.

53 questions
Filter by
Sorted by
Tagged with
5k views

### How to calculate the frequency of oscillation of this low-pass phase shift oscillator?

In the following phase-shift oscillator a low pass network is used instead of a high-pass network. simulate this circuit – Schematic created using CircuitLab Usually the frequency of ...
• 639
1 vote
592 views

• 3,965
266 views

### Attenuation - two stage RC low‐pass filter

I am having trouble with finding the attenuation and bode diagrams for this circuit below. This circuit is two stage RC low-pass filters. I have been trying to find resources on how to do them with ...
6k views

### How to calculate phase shift of a low-pass filter's output?

I'm simulating a basic low-pass RC filter in Proteus, and I need to find the phase shift of the output at varying frequencies. I've plotted a frequency response graph which shows the phase against ...
• 147
524 views

### How to speed up charging of output capacitors of ADXL335?

Problem statement I need to obtain as fast as possible after power-up a reading from an accelerometer. The accelerometer is located in a car and is powered by the same rail of the rear braking lights,...
• 1,316
2k views

### Flash an LED to music

Im trying to flash an LED to music. I have tried to follow this article and calculate values but cannot get it to go. Basically what i think i need is: audio in through a low pass filter (isolate ...
• 572
1 vote
1k views

### Unexpected behavior of the Sallen-Key second order filter

I met an unexpected behavior when I simulated under Multisim (National Instruments) the Sallen-Key circuit given on the image below. The circuit is designed to receive a 1.8kHz modulated sin wave as ...
• 13
1 vote
460 views

### Is this correct for non-inverting op-amp?

Do 0.1 uf and 100 k ohm act as low-pass filter in here?
• 185
1 vote
608 views

### Frequency response of a low-pass, band-pass, and high-pass adder circuit

I'm doing a project and one of the steps consists of filtering a signal through a low-pass, band-pass and high-pass filter. All the filters are Sallen-Key with a passband gain of 1. The pass-band ...
1 vote
5k views

### Why do RC circuit voltages decay *slowly* rather than instantly?

Let's take the simplest RC circuit imaginable: simulate this circuit – Schematic created using CircuitLab Now I think I properly understand why the voltage rises slowly after the leading edge ...
• 185
1 vote
114 views

### Butterworth and Chebyshev filter problem

Find the minimum order Butterworth lowpass filter whose attenuation isn't bigger than 2 dB at 5 rad/s and has 10 dB at 8 rad/s, 20 dB at 10 rad/s, and 40dB at 30 rad/s, then do it for Chebyshev filter....
• 13
1 vote
385 views

### Getting rid of noises after RC low pass filter stage

I am outputting a 40kHz square wave from arduino and passing it through an RC circuit in order to get a clean 40kHz sinusoid out. However, the output wave I am getting is noisy.(see picture) Any ...
1 vote
1k views

### Resistor placement in filter circuits

Why does the placement of the resistor in a filter circuit matter? I've heard if you switch an inductor and a resistor in a series circuit it could change the type of filter you get. Ex: From a low ...
• 15
1 vote
1k views

### BJT Active low-pass filter frequency calculation

The left BJT of this circuit acts as a low-pass filter. According to Simple transistors Low Pass filter, where I found this schematic, its cut-off frequency is 150 Hz. How do we calculate this ...
• 55
1 vote
3k views

### lead high pass filter and lag low pass filter

I have a question regarding lead high pass filter and lag low pass filter. I do not quite understand the reasoning behind these two special case (when z=0) ? Thanks!
• 497
1 vote
151 views

### How much gain I am getting and with the 2 stage transistor amplifier attached with a Global NFB [duplicate]

This is just a direct manual solving directly subtituting values in a formula with disregard to temp etc. Sorry for the incomplete information here are the goals of this: "gain of 100≤Av≤130 and ...
• 23
313 views

### Sallen-Key Low Pass filter

I was trying to do a project on LT spice for the frequency response for Sallen-Key low Pass filter. But when I tried the Following circuit, I am getting a roll off 20db / decade instead of 40db/decade....
• 13
1k views

### Low-pass LC filter on both sides of a motor

I'm building an H-bridge to control a load. The design is done, and all that's left is to filter out the switching frequency. The switching frequency is at 20 kHz, and since the current flowing ...
70 views

### Output voltage at different output optical chopper frequencies

I have a circuit as shown in the figure and I am using it to extract output voltage of thermopile (to determine the time constant of thermopile ) at different output frequencies. The optical chopper ...
• 11
89 views

### Need help with pulse sensor design modification [closed]

So I've got the below pulse sensor design. I don't understand why they filter before they amplify. I'd like to modify it in a way that I amplify the signal first, LPF second, HPF last. For some reason ...
59 views

### Input across RC circuit is not showing a square wave though the input is a square wave [duplicate]

I wanted to observe the transient response of the capacitor so applied a square wave of 205mHz from a function generator as that would allow complete charging and discharging for the capacitor in the ...
163 views

### Cascaded Filter Output Not Correct

I am simulating a speaker system with tweeter, woofer, and midrange speakers. I know my values for the components are all correct, but the output plot is a little off. The passbands should be a little ...
• 21