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

learn more… | top users | synonyms

1
vote
2answers
46 views

How to measure cutoff frequency of a low pass audio filter?

I've built a low pass filter for use in a synthesizer and would like to measure the cutoff frequency compared with various different control voltages to profile its characteristic. I have access to a ...
0
votes
1answer
63 views

Low Pass Filter For Square Wave Through An Optoisolator

I've got a higher voltage square wave input that I'm feeding through FOD817B Optoisolator. The square wave frequency is in the range of 30 to 300 Hz. The Circuit is like this: simulate this ...
0
votes
2answers
72 views

Matlab low pass filter design -removing noise

I am designing a low pass filter in matlab to remove the noises shown in the image. The original signal of interest lasts only for about 80 ms and rest of the signal are noises from probe tip. In ...
1
vote
3answers
69 views

DSP Cutoff vs Sampling frequency question on low pass filter

Is it unrealistic to have a 125 MHz sampling rate with a cutoff frequency of 5 Hz? I downloaded a few filter programs and used their methods and it seems that even with thousands of taps it still ...
1
vote
1answer
31 views

What are these things called in a bode plot

Here is a low pass filter bode plot: In the bode plot theory, what is K called? What is ω0 called? What do these two represent for a low pass filter? Does K not represent an amplification or ...
0
votes
1answer
65 views

Low-Pass filter on AVcc pin for ATtiny

The datasheet for the ATtiny861a states that "If the ADC is used AVCC should be connected to VCC through a low-pass filter". The datasheet doesn't specify what values I should use or what style of ...
0
votes
1answer
51 views

What to do with the Balance and NC pins?

For a course project, we are to use an LF356 operational amplifier What does the Balance and NC do? and I do not think I need it for my project(Sallen-kay filter 4-pole). Do I just ground it?
3
votes
2answers
389 views

Obtain an accurate DC value in an AC+DC signal

Background: My goal is to use an Arduino with two proximity probe sensors to achieve some output. It is worth mentioning that the output of the proximity probe has two components: DC output that ...
0
votes
1answer
39 views

Dual passive low-pass filter

I am building a class D amplifier and need to design passive low-pass filters for H-bridge with cut off frequencies at about 400 Hz. However, I am unsure about few things, this is the simplified ...
0
votes
1answer
77 views

Digital Low-Pass Filter When Oversampling Audio

The human ear can hear sounds up to ~ 20KHz. Some ADC's oversample. For example, to capture frequencies up to 20KHz, an ADC converter might sample at 160KHz. The steps are: 1. Filter the audio with ...
0
votes
1answer
62 views

Current regulator with controller?

I want to implement a circuit which allows to regulate the current flowing to the load. I have two use cases: Case 1 is the normal case where I would set the max. allowed current with a ...
0
votes
1answer
60 views

Filtering noise off of PWM signal

I am trying to measure the resistance of a nichrome wire that has a PWM (1000Hz and different duty cycles between 0 and 100%) voltage applied to it from a 5.0V regulator. The setup I have in mind ...
0
votes
1answer
126 views

EEG amplifier circuit low and high pass filters. Oscillations, noise, etc

I designed a EEG amplifier circuit for for EEG signal amplification and filtering. Because I never had any experience in filters, It would be highly appreciated if someone could check my design. In ...
1
vote
1answer
94 views

Low Pass Filter calculation

I am designing a circuit which reads a analog signal(DC - Response from a photo-diode exposed to tungsten lamp) to a 12 bit ADC. The ADC is MCP3202 running at 1Mhz speed and uses 16 input bits to get ...
2
votes
1answer
242 views

Input impedance of PIC32 ADC pin

I want to measure temperature of an oven using a thermocouple. The maximum change in the temperature will be 1oC/s. The amplifier section will already contain a low pass filter, but I want to put an ...
0
votes
3answers
87 views

Which low pass frequency filter to configure to measure/calculate DC-DC converter efficiency?

I am measuring the DC-DC converter active power (P in watts) efficiency of a TI (Webench) LM3150 PCB that converts 12 to 5VDC. In the answer of question Measuring precisely the efficiency of a power ...
1
vote
2answers
84 views

Low-pass filter for high power application

I'm designing a LP filter that should be used for a load of up to 2000W. I want to filter the AC voltage that supplies a controlled heater which uses a TRIAC for control. I've tried one approach but ...
-1
votes
1answer
100 views

RC low pass filter PCB layout limitation

I have an RC low pass filter for debouncing a GPIO pin. Do I have to place the resistor and the capacitor close to each other? Currently the capacitor is near the GPIO pin, and the resistor can be ...
0
votes
1answer
96 views

Help understanding 60 Hz low pass filter behavior in oscilloscope

I have been testing this circuit in simulation which is supposed to be a low pass 60Hz filter, as far as i am concerned the simulation works as intended in simulation starts filtering frequencies ...
2
votes
2answers
332 views

Should I always put a low-pass filter on an ADC input?

I'm a recent hobbyist EE and new to micro controllers. I've built a test circuit to make measurements with a type K thermocouple, a PT1000 as well as an oxygen sensor. The weak signals go through a ...
1
vote
1answer
58 views

Transfer function of a cascaded passive + active filter

How do I get my H(s) transfer function from this circuit? If there was infinite impedance between the two filters, I'd just do H_LP (s) * H_HP (s). However, we are assuming that the input/output ...
4
votes
2answers
289 views

What is the steepest roll-off achievable for an analogue low-pass constructed with a single op-amp?

I was wondering about this question. What if the only design requirement is having the highest steepness of the roll-off but using only one op-amp? I know it's possible to construct approximations of ...
2
votes
2answers
158 views

Calculating SNR after lowpass filtering

I am currently working with a sinusoidal signal buried in noise. I filter the signal with a low-pass filter of which I know the transfer function. How can I calculate the SNR after the filtering ...
3
votes
3answers
188 views

Tool to calculate cascaded but independent single-pole RC hi-pass filters

I frequently use a single op-amp stage for both gain and hi-pass filtering. I normally implement 2 independent single-pole low-pass filters: the input to the op-amp and the ground end of the ...
4
votes
1answer
72 views

For IIR low-pass filters, what design provides the least amount of phase shift in the pass band?

Given all the possible design options for IIR filters one could consider (e.g. Butterworth, Chebychev, inverse Chebychev, elliptic, Bessel, etc.) which design provides the least amount of phase shift ...
1
vote
1answer
103 views

Transfer function of a R+RLC low pass filter

Here's a picture of the R+RLC circuit: I'm trying to find the frequency response of this low pass filter, my solution is below and please let me know if there is anything wrong with it. My ...
1
vote
4answers
452 views

Low pass filter issue - is the 10k resistor part of the circuit?

This may be a really simple question but Op Amps still confuse me a little. I have a low pass filter circuit as shown below. My question is whether the 10k resistor is part of the filter circuit ...
0
votes
1answer
80 views

Transfer Function Of Multiple Feedback Filter - with a difference!

I posted a question yesterday about a circuit i thought was a low pass filter, however it turns out to be a transimpedance amplifier and a 2nd order low pass filter all in one! The input signal is a ...
0
votes
0answers
65 views

Op Amp Low Pass Filter - Feedback not connected as expected?

I have come across a circuit which I think is an active low pass filter, but it seems to have a few differences from the standard circuit I am used to seeing. Referring to the schematic, I am not ...
3
votes
3answers
260 views

LC lowpass filter optimization

I have some 12 volt cooling fans which interfere with a radio transmitter. I notice that if I either put a large capacitor in parallel, or a large inductor in series, I can eliminate the noise heard ...
1
vote
2answers
174 views

Class D amplifier woofer filter designs

I am working on a 140W class D amplifier for my subwoofer. I am familiar with its topology but have few questions. The music source is a radio that ouputs 200mV peak-to-peak signal containing all ...
1
vote
1answer
212 views

Low Pass Filter With Hall Effect and ADC Help

Background: I am using the Allegro ACS758KCB-150U hall effect based current sensor, here is the datasheet, I am using it to measure current drawn by 24V motors, between about 20A - 130A. The reason ...
2
votes
3answers
257 views

Analog preprocessing circuit (anti-alias/pre-amp) for driving ADC

Background Similarly to what Jeri Ellsworth did in her C64 Bass Guitar hack I am working on an audio-to-midi converter for my bass guitar. I am also planning to use piezo discs as sensors placed ...
0
votes
2answers
191 views

LM358 Single Supply problem

I am trying to build a low pass filter circuit from the LM358 datasheet from TI. Looking at the pinout and building the circuit I cannot get something basic like this filter to work. I have everything ...
3
votes
3answers
153 views

Trying to determine the output of a RC-filter with load

I have a low pass filter like this: simulate this circuit – Schematic created using CircuitLab \$V_{out}\$ is measured right after \$R_1\$, which I suppose means that it is measured over ...
4
votes
1answer
133 views

Basic Filter Design

Need help with basic filter design. Firstly there is a low-pass filter(pictured below). I am supposed to derive an expression for the amplitude of the output voltage as a function of \$R_1\$, ...
2
votes
1answer
108 views

Op-Amp difference amplifier low-pass filter

I have the following (summing, single supply) difference amplifier circuit: How can I extend this circuit to a 1st or 2nd order low pass filter, with a corner frequency at about 20kHz.
0
votes
3answers
159 views

How can I achieve symmetrical analogue low-pass filtering?

I am experimenting with VCFs for an analogue music synthesiser. Initially I tried a 3-stage low-pass filter based on the sinewave-generator circuit in the LM13700 datasheet but having removed the ...
2
votes
2answers
938 views

A simple RL circuit, getting transfer function, matching with results

I'm doing little lab exercise with an RL circuit. I need to check if I did this analysis right, because the numbers I got and the numbers that should theoretically be there are so far off, I figured ...
0
votes
2answers
368 views

What happens to a DSB signal if I use an envelope detector instead of Low Pass Filter

What happens to a DSB signal Modulated signal if I use an envelope detector instead of Low Pass Filter ? I am interested in knowing how the output signals vary in case of a envelope detector. I know ...
0
votes
2answers
75 views

Singnals, filters and power output

I have couple of questions: A square signal goes through a low pass filter and in the output of a circuit we get a sine. What happens there? Give a scheme? This is really weird, because, from what ...
0
votes
1answer
69 views

Input to amplifier with LPF not working

I am trying to build a pink noise machine to use at work. See schematic below. If I connect the output from the MM5837N (noise generator), directly to the amp circuit. It works fine, and is nice ...
0
votes
1answer
206 views

Low-pass filter for digital input

I made a digital input circuit to convert a 120Vac waveform into a digital 2.3V signal. I would like to add a "low-pass" filter at the output to get a low level for higher frequencies than 1kHz. I ...
1
vote
2answers
357 views

Reducing Ripple in the Zener Regulator

In the Art of Electronics (Horowitz & Hill) the following circuit is given as a solution to reduce ripple current caused be variations in input voltage (pg. \$ 69 \$): "An alternative method ...
0
votes
1answer
229 views

Low pass filter value for DAC

I was wondering, how to calculate the values needed for LC/RC filter when using it for digital to analog conversion? Also, how does the square waves frequency affect DAC ? For example: lets say I ...
1
vote
2answers
100 views

Why would an 8-order LPF switched capacitor has a least steep roll-off curve (max7405)?

As far for my understanding, a higher order LPF will have a steeper roll-off curve. Something like below would happen if we increase the number of order for the LPF: Normal LPF frequency response ...
1
vote
2answers
290 views

Variable Voltage Using PWM and Low Pass Filter

I am trying to control a steady DC output voltage using a Micro controller with a PWM duty cycle. With the current schematic, the Voltage on Vout is pulsing along ...
1
vote
2answers
869 views

What do you mean by -3db cut off frequency in low-pass-filters?

I have a low pass filter as follows. simulate this circuit – Schematic created using CircuitLab Using voltage divider I get $$\frac{V_{out}}{V_{in}} = \frac{1}{\sqrt{1+(\omega RC)^2}} ...
1
vote
1answer
256 views

What Load impedance to use for LC Filter before transformer?

I have an inverter circuit in which I want to filter the output with an LC filter. Lets say the fundamental component that I want is 60Hz. When designing a Low Pass LC filter, I need to use the load ...
2
votes
1answer
372 views

How to build LED dimmer for room illumination - PWM, low pass filter?

I want to illuminate a room. This will be done by two LED strips 60led/m, each 5m long, located along the tops of opposite walls. In order to get full light power, they together consume 4A@12V. ...