Questions tagged [low-pass]

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

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1 answer
276 views

How can I only let a specific frequency pass in an AM receiver?

I wanted to create an AM receiver and I know partly how to demodulate the signal. I know I need to use a low pass filter to get the low frequency audio signal, but I don't know how to only get data ...
-1 votes
1 answer
123 views

Transient analysis of the low pass RC filter

I have designed a low pass RC filter and trying to simulate using transient analysis. I can't figure out the magnitude of the input and output waveform. What's the time delay between the input and ...
0 votes
1 answer
59 views

Capacitor "blocking DC" in a low pass filter [duplicate]

If we imagine a basic lowpass filter, the AC components from the non perfect DC from VIN passes the capacitor and down to ground, meanwhile "pure" DC flows to VIN. If we take a basic closed ...
1 vote
1 answer
2k views

How do I know to choose a first order filter vs a second order filter?

I have a DC signal coming off of a battery. The Arduino is reading the voltage. The issue is that the voltage signal contains a lot of noise (120hz frequency). I am planning on building a first order ...
1 vote
1 answer
32 views

How can I calculate filter parameters between RF switch and antenna?

In the schematics en.MB1389-WL55JC-highband-E02_Schematic, there's a Pi filter following the RF switch before it links to the SMA connector for the antenna. Upon calculation, I found that the cutoff ...
0 votes
0 answers
26 views

Raspberry Pi DAQHAT: Overvoltage issue

I am working on development for a piece of HV test equipment, where I need to monitor the voltage output for a circuit that is actively arcing. I am measuring the voltage off of a Raspberry Pi DAQHAT (...
0 votes
1 answer
59 views

Should you include multiple low-pass capacitor circuits in integrated IC PCB design?

I have two circuits, one is a POE to 5V, another is an IC for leds. They both include capacitors between 5v and gnd. Should I include the first 5V circuit POE capacitors since it should already be ...
0 votes
1 answer
55 views

High R for low frequency op amp integrator

I have to design an integrator for very low frequencies (corner frequency around 0.5 Hz). Are there any reasons why I cannot choose a really high resistor value (say 5M Ohm) to keep the capacitor ...
0 votes
1 answer
53 views

Negative capacitance circuit without relaxation oscillations

Wikipedia gives the following circuit as a negative capacitance circuit: I was curious if I would be able to create a low-pass resistor-negative-capacitance filter, analogous to an RC low-pass filter,...
0 votes
1 answer
33 views

PWM Low-pass filter for LCD contrast pin with a potentiometer?

As a software developer, electronic engineering isn't my strong suit, so I'm struggling to understand some simple concepts regarding this circuit. This is a unique circuit I have encountered that is ...
0 votes
1 answer
896 views

RC Laplace and time domain

Another basic question to understand. It is well known that the transfer function of a low pass RC filter in Laplace domain is \$V_o(s)/V_i(s)=1/(1+sRC)\$. Now sticking to this format and taking ...
0 votes
2 answers
44 views

Low-pass filter with a load

how can be the voltage of a low-pass filter be mathematically described when a load is connected? Is it possible to ignore the effect of the load on its voltage as something like this circuit can be ...
1 vote
0 answers
92 views

How to design an inductor for the output of a low-pass filter for a 10 kVA sinusoidal UPS

The problem is that I have a 10 kVA sinusoidal UPS to repair and after replacing all the IGBTs and other components, I noticed that the low-pass filter output inductor is getting very hot at around ...
12 votes
4 answers
4k views

Is a 100 Ω/1 nF RC low-pass filter enough to protect a microcontroller I/O pin from ESD?

While researching ESD protection on this site, I came across this question. The answer by Peter Smith contains a comment by @Ale..chenski: Just a nit pick: if you can afford 100R and 1nF to ground on ...
1 vote
1 answer
126 views

Loss of 2nd order behavior on 2nd order low-pass filter

I have a 2nd order Sallen-Key Low-pass filter, cut-off frequency of 170Hz. When attached to a perfect source, this is the bode plot. As expected, 40dB/decade response. The low-pass filter is used as ...
3 votes
1 answer
9k views

Passive Pi Low Pass Filter LC

I'm trying to use a simple pi low pass filter using two capacitors and one inductor. I've found the formula to calculate the value of the capacitance and of the inductance using the cut off frequency,...
0 votes
1 answer
84 views

Combining voltage divider, pull-down resistor and low-pass filter in analog sensor signal

I am integrating a KP236N6165 analog absolute pressure sensor from Infineon. They recommend the following circuit : My microprocessor which receives the signal uses 3.3V logic and is not 5V tolerant ...
0 votes
1 answer
55 views

Is it good to equalize input impedances in cascade active opamp filters?

In my design, I designed a first 2nd order high pass filter with a Sallen key cut-off frequency of 0.2Hz and an input impedance of 250kohm. Then, I designed a second-order Multiple-Feedback low pass ...
0 votes
0 answers
50 views

what is the purpose of the additional resistors and capacitors in the reference design of the multiple feedback fully differential low pass filter?

What is the purpose of the additional resistors and capacitors added C14 R12 R14 R13 R15 C15 in the reference design of the .second order multiple feedback fully differential low pass filter? ...
0 votes
0 answers
71 views

Trying to power a 12 V LED underglow system using PWM signal from dome light

I've learned a lot from the brilliant minds on this forum so far, and I think I've narrowed my original question a bit. I'm trying to create an entry light effect in my car using my LED underglow ...
1 vote
3 answers
383 views

Suppress noise on digital signal

Tasked with improving on an existing design, I need to read pulses using a reed sensor excited with a magnet, placed on the front wheels of motorbikes. The system's core has changed, moving from a PIC ...
2 votes
1 answer
115 views

strange phase behavior RC low pass filter

I have a low pass RC filter (R=12Ohm, C = 22µF) Which is showing some strange behavior in the phase shift. The cutoff frequency is around 600Hz, as calculated. But the phase shift goes to -45° only at ...
3 votes
2 answers
158 views

Non-standard low-pass filter design

While experimenting with various low-pass filter topologies (audio application), I came up with the following design: simulate this circuit – Schematic created using CircuitLab It seems to ...
1 vote
1 answer
78 views

Purpose of this resistor in a low-pass filter

I found this filter configuration on one of older soundcards: simulate this circuit – Schematic created using CircuitLab V1 here is the DAC output with a positive voltage offset. What is the ...
0 votes
1 answer
134 views

About PLL input frequency

I am working on a PLL design. I am at the research stage now. I am confused about the PLL input frequency range. This frequency has to remain constant. If this input frequency stays constant, how can ...
1 vote
1 answer
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 ...
0 votes
3 answers
280 views

Is this transistor amplifier with low pass filter correct? How should I measure the gain and frequency range?

My goal is a gain of 100-130 and a frequency range of 1-10 kHz.
2 votes
2 answers
67 views

Differential DAC filter capacitor options

The standard output filter for a DAC with a differential voltage output looks this way: simulate this circuit – Schematic created using CircuitLab However, some DACs have this filter ...
1 vote
1 answer
7k views

Critical damping of SMPS LC filter

I am designing a damping resistor [minimum load of SMPS] in parallel to output capacitor of LC filter. SMPS specs: 1. Vout: 200 V 2. Iout [Max]: 2 A 3. PWM frequency: 50 kHz Output filter specs: 1....
0 votes
1 answer
103 views

RC-filter transfer function confusion

simulate this circuit – Schematic created using CircuitLab I have a question about the transfer function of the above RC-lowpass filter. If I switch places of the capacitor and the resistor to ...
1 vote
0 answers
38 views

Sallen-Key filter with input signal attenuation

I want to reduce input signal amplitude before it gets to the low pass filter by 6dB. I could use MFB topology for K<1, but that would invert the phase. Is there a solution that keeps the phase? ...
0 votes
0 answers
59 views

Trouble understanding resulting bode plot while getting hands on filter design

Recently tried to get hands on filter design, I tried to design à simple low-pass RC filter as shown here. simulate this circuit – Schematic created using CircuitLab Cutoff frequency must be \$\...
0 votes
0 answers
71 views

LTC 2065 is not working between 2 V - 4 V power supply

I'm having a problem with the LTC2065 operational amplifier design. I use a 3.3V supply as I show in the picture, and after boosting my input signal I make it oscillate at 1.8V using a 1.8V virtual ...
0 votes
1 answer
87 views

Non-constant active filter gain

I designed an amplifier using an instrumentation amplifier and an operational amplifier. Here, I used a 2 Hz high pass and 100 Hz multi feedback low pass filter, but I could not get the efficiency I ...
0 votes
1 answer
79 views

Problems with output signal of a 2nd order low pass Sallen Key filter for an electret microphone

I'm having problems with a small circuit based on the amplification of a audio signal received by an electret microphone. It goes to a 2nd order Sallen Key low pass filter circuit with an ...
0 votes
2 answers
493 views

Placement of RC filter used for EMC filtering

I've seen RC combinations used on many circuits now which I believe have been included for EMI filtering. They usually feed off to a connector. Does the placement of these matter in the circuit? Let's ...
0 votes
1 answer
93 views

lowpass prototype to bandpass filter

Bandpass filter with a center frequency of 10 rad/sec and bandwidth of 20 rad/sec here, wo= is mentioned as geometric frequency that's why I am confused. The solution in which picture is correct?
1 vote
0 answers
80 views

Resonant circuit in class C amplifier

Questions What is the better option when maximum efficiency of class C amplifier is needed: LC circuit between VCC and drain of amplifier + low pass filter RF choke and low pass filter simulate ...
1 vote
1 answer
308 views

Choosing RC values for Active LPF to match signal input impedance

I am design a basic 1st order Active LPF with unity gain and am new to this field. How do I make sure that I choose my R and C values to match the input signal impedance or does this not matter? What ...
1 vote
1 answer
103 views

Differential Mode EMI Filter Design for DC Power Input Noises

https://www.murata.com/en-us/products/productdata/8796777775134/ENFH0008.pdf https://www.digikey.com/en/products/detail/murata-electronics/BNX022-01L/1825573 Hi everyone, I try to understand this ...
2 votes
3 answers
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 ...
6 votes
4 answers
816 views

Simple low pass digital filter implementation for non-uniform sampling?

I have a system sampling an analog input and I want to filter that value using a simple, first order filter. EG something of the form: Yn = A*Xn + B*Yn-1 However I have no control over the ...
0 votes
2 answers
426 views

Why does this negative impedance converter (NIC) circuit work in an LTspice simulation but not in an actual circuit?

I've been trying to invert the phase response of a non-inverting low pass filter by using a "negative resistor" (-5000 ohms,) which is achieved by the simulation below (bode plot + circuit): ...
2 votes
1 answer
91 views

Connecting low-pass filtered output of one comparator into a second comparator

I have the following situation: I have a signal with periodic, short (~2ns), ~1.5V pulses spaced ~10-20ns apart. I would like to detect when the pulses disappear, i.e. when there is no pulse for ~1us ...
1 vote
2 answers
55 views

Trying to make a glorified aux splitter, but it won't work

I have a project due in a couple of months, and decided I want to make a aux splitter where you can control the volume of left and right on two inputs and get a single output, kind of like a mixing ...
3 votes
1 answer
440 views

How to improve the performance of my low pass filter design

Goal: I am designing a low-noise, 8-pole, low pass filter to use in the output stage of a lock in amplifier. The filter needs to attenuate wide-band noise and a doubled carrier frequency in the range ...
2 votes
3 answers
101 views

Are RC /CR - Highpass filter the same?

I‘m quite new to electrical engineering and one of the tasks is to showcase and plot an CR high pass filter. I am familiar with RC HP filters but this is new to me. Just changing the order of the ...
0 votes
1 answer
72 views

Can't derive transfer function of RC filter with load

I am trying to go along with an example on a simple RC filter with load in a book called Practical electronics for inventors. simulate this circuit – Schematic created using CircuitLab Although ...
0 votes
1 answer
52 views

Is there a reason to use different sets of resistor values in the 2 stages of a butterworth LPF?

I needed a LPF for my design so I used Filter Design Tool from AD to generate one. The generated circuit includes 2 sets of resistors of different values, which I find inconvenient. Is there a reason ...
0 votes
1 answer
57 views

Ideal Low Pass Filter shifted is still ideal Low Pass Filter?

maybe a stupid question. But let us say we have a ideal LPF filter like this: $$H\left(j\omega \right)=\begin{cases}1&-\omega _m<\omega <\omega _m\\ 0&else\end{cases}$$ If I shift it , ...

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