Questions tagged [low-pass]

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

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52 views

Determining values to convert square wave to sine wave at low frequency

For a project I am working on, I have a 1Hz square wave coming from a real time clock, and need to convert it into a sinusoidal wave to pulse LEDs. After some googling and playing around with ...
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137 views

Low pass filter not working properly

This is the pass band that I'm using to filter some EMG signals through electrodes. When I test it with multisim it works really well as you can see, but when I test it with real equipment (...
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How does a RC Lowpass filter work?

So I've been trying to understand how an RC lowpass filter works, and I think I got it, but I just need some clarification. My understanding: So an RC Lowpass filter in a nutshell is just a voltage ...
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adding rc filter to cheap sub

I bought a cheap computer Sub to repurpose it as a selfmade gaming vest. The circuit has 2 amplifiers on it, one for the normal unfiltered sound that goes to the 2 speakers, and then the output of ...
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1answer
79 views

Synthesizing this simple analog notch filter?

I want to synthesize this simple analog audio filter which is a notch: The inductor with resistor creates a simple one-pole low pass filter with the cutoff frequency at: fc = 1/(2pi L R) The ...
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72 views

Lowpass Audio Filter on FPGA

I am trying to establish a low-pass filter to Audio Demo code of Nexys A7 board. I have implemented a filter however I hear just a noise. If you share your time, I will be happy. I have added the ...
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1answer
47 views

How does adding a capacitor change the frequency response of this inductive LPF?

I know that a simple circuit like this in an ideal case will have a frequency response of a single pole LPF, where the cutoff frequency is given by: cutoffFreq = 1/(twoPi*L*2R) This is reviewed here....
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76 views

Low-pass cutoff frequency definition (-3dB vs. filter design)

For low-pass filters, we usually define the cutoff frequency as the frequency at which the gain drops by -3dB. Another definition, however, comes up in filter design as one of the parameters that ...
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59 views

Does any practical RC circuitry exist which will perfectly cancel out a pole?

Firstly, some basic theory…. The transfer function of a simple low pass filter is:- This transfer function has one pole. The gain goes from 1 to almost zero as frequency increases and the phase goes ...
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3answers
51 views

Design of second order low pass filter using passive RC components and opamp

I have an RC low pass filter connected to the non inverting terminal of the opamp. There is a feedback resistor from output of opamp to its inverting pin.Then an RC low pass filter is placed at the ...
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1answer
56 views

Is this transfer function impossible with a low-pass Sallen-key filter?

I was given this transfer function and instructed to use a Sallen-key cascaded with a 1st order filter to achieve it. $$H(s)=\frac{628^3}{(s+628)(s^2+628s+628^2)}$$ The first order transfer function ...
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4answers
48 views

Trouble designing a low pass filter

I was trying to design a simple 3rd order low pass filter by cascading 3 first order low pass filters along with an amplifier at the end. The transfer function is straightforward: $$ H(j\omega )=4\...
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Why is inverting op-amp behaving like a low pass filter?

can anyone explain why this circuit behaves like a low pass filter despite having no capacitor in the feedback loop?
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1answer
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Configuring TI TPA6138A2 for Single-Ended PWM Inputs

I'm looking to use the TPA6138A2 to ground-center, LPF, and amplify 2 PWM inputs (between 0 and 3.3 V). My desired LPF cut-off frequency is 18 kHz and I would like to use a digital potentiometer for ...
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16 views

Should Passive LPF/HPF Component Selection Depend on Ability of Input to Source Current?

When choosing R and C for a passive LPF or HPF, should you take into account the input's ability to source current? I'm currently working on a passive HPF for an input that can supply up to 10 mA @ 3....
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Combine High and Low-pass filters to create 2-way crossover

I am in a bit of a dilemma. I was given 2 Bose tweeters (8ohm) and a Bose woofer (2ohm). They came with a build in amplifier which I want to get rid of as it makes the system unnecessarily large. I ...
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1answer
30 views

How to Cascade Filters and Audio Volume Control

I am trying to output PWM from an MCU, filter it with a LPF to form an analog signal, cascade an audio volume control that allows for smooth control between silence and a somewhat amplified signal, ...
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34 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 ...
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1answer
84 views

Questions about the baxandall circuit

So I understand that the baxandall circuit is a tone control circuit, able to configure a bass and treble through RC filters. The general understanding I have from it, is that the capacitance of the ...
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74 views

Accelerometer to detect when product has been picked up by user

I have a 3-axis accelerometer on my board and i was hoping to use it to detect when a user lifts the device up. I would like to avoid false triggers when the table shakes or when the user nudges the ...
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37 views

How does a high pass filter and a low pass filter work for an amp?

I'm researching how to incorporate treble and bass into an amp. X1 is for bass, X2 is for treble and X3 is for volume. Intuitively, for me, if a high pass filter only allows frequency above a ...
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87 views

Low Pass filter with a resistor

simulate this circuit – Schematic created using CircuitLab Hello i am learning about filters and make this circuit in many circuit simulators. When i increase the R2 resistance the voltage ...
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2answers
115 views

DC ripple stabilizer. 3rd order low pass filter. How to supply op-amps properly

I have a cheap ac-dc adapter, but it outputs DC with a ripple. It has variable output, so it can output 12, 14, 17, and so on up to 32V. I measured output of ac-dc adapter with an Agilent multimeter, ...
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3answers
93 views

Differential filters: high pass, low pass, band pass

I am looking to use a band pass filter in an EMG circuit design using the differential signals you receive from an op amp (differential/instrumentation). I have been looking for what is the proper way ...
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1answer
95 views

How to implement a lowpass filter for this one zero, one pole transfer function?

I have a task where I need to implement a filter circuit (active) for the following transfer function: $$G(s)=\frac{(s-5447)}{(s-961.3)}$$ So, we have one pole and one zero. The bode plot is as ...
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1answer
82 views

Differential low pass filter to single ended -> Differential low pass filter

I'm designing an audio DAC based on the PCM1690 from TI. Datasheet One requirement of the DAC is differential outputs. Since the PCM1690 has differential outputs, this is not a problem. However, the ...
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40 views

Impacts of low-pass filter on micro-controller board

I have a micro-controller board, driving small DC servo motors and I control the angle via a PWM signal (50 Hz) and everything is alright. However, there is an oil gas motor, running next to the ...
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2answers
81 views

Why does adding this low pass-filter to a monostable multivibrator prevent triggering?

A 24 VDC sinking sensor is tied to an SSR. The SSR converts the signal from 24 VDC to 5 VDC. The output of the SSR goes directly to input B of a 74121 One-shot. (The diagram has a resistor and ...
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1answer
98 views

How could this circuit be reduced to first order low pass filter?

I was told that the bottom half of the circuit wouldn't matter due to having a corner frequency being significantly higher compared to the top half, or due to time constant (somewhere along this line.....
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1answer
65 views

DC Power Line Communication (PLC) low pass filters

I've seen many times that a low pass filter needs to be implemented before a switching power supply in DC power line communication transceiver boards. Why is that? I assume that the switching power ...
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1answer
78 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 ...
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How do I measure the fluctuation of a pulsed voltage of ~1700V?

The problem: See the little sketch. Starting from a high-precision DC power supply, I pass the voltage to low-pass filter and a pulser. This pulser pulses the nominal voltage of around ~1700V down to ...
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1answer
57 views

open-circuited stub VS stepped-impedance

What is the difference between open-circuited stub and stepped-impedance ? The open-circuited stub microstrip realization method is a modification of the stepped-impedance microstrip realization ...
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1answer
121 views

Active filter has unintended attenuation for lower frequencies

I have design an active filter with an online tool. The circuit looks as follows: It should be a low pass filter of 3rd order with a cut-off frequency at 50kHz. Unfortunately, it attenuatues DC ...
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1answer
57 views

How does one calculate the values of LF1&2 and C93?

I am learning about USB circuitry and one of the example schematics uses this lc low pass filter. I want to understand where these values came from? Thanks in advance. Link to article
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44 views

Understanding a low pass filter used in a HV circuit

I have been given the following circuit: The input of this circuit is a 3.3 kV DC signal. The filter is there to stabilize high frequency ripples that might appear on the supply line. As far as I ...
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3answers
103 views

Shifting level voltage of a signal

I have a signal, which can vary from 400 to 7000 Hz approximately. It is a kind of pwm signal and has the time of high level, Ton, 30 times longer than the time of low level, Toff. The shape of the ...
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2answers
198 views

Filtering an ADC input with an RC low-pass filter

I use an instrumentation amplifier to amplify low voltage signals from a sensor. The max. amplified output voltage is 3V. Im using this ADC: http://ww1.microchip.com/downloads/en/DeviceDoc/22088c.pdf. ...
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2answers
261 views

LTSpice Sallen-Key Filter

I'm new to simulations on LTSpice with op amps (and LTSpice in general). I've been trying to simulate a Sallen-Key low pass filter and the simulation is nowhere near my calculations plotted with \$...
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50 views

microstrip low pass filter design issues with sonnet

I am trying to replicate the microstrip low-pass filter in SonnetLite from the book by Jia-Sheng Hong - Microstrip Filters for RF Microwave Applications, 2nd Edition (Wiley Series in Microwave and ...
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2answers
66 views

Trouble getting measurments of my circuit

I'm trying to turn the first image in a multisim circuit but i can't get the right measurements. I have tried a vcc power source but i still can't get the right result in the oscilometer can anyone ...
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49 views

How to Implement this BEMF Observer

I'm using the lecture by Dave Wilson at TI to implement a BEMF observer. I have the motor winding currents for phase A, B and C. I also have the Bus Voltage I also am in the stationary reference ...
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1answer
152 views

Topology for ideal cutband response (-20dB per decade per order) for passive, low pass, constant output impedance filter

I am trying to develop a low-pass constant output impedance filter. The output impedance must be within ±10% of 5Ω from DC up to 1GHz. The filter is driving an open load (>10M) and must filter current ...
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64 views

(Inductor) Low-pass filter for current signal

I'm using resistors in a series circuit to vary the resistance between a constant 12V supply line and ground. Using transistors, the current either flow through all resistors, or is routed to ground ...
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1answer
37 views

In RC LPF, what is the magnitude at the pole location?

In RC LPF Transfer funciton = 1/1+sT, the pole location is -1/(time constant). So As per the pole concept the magnitude response at this pole should be infinity. But why it is -3dB?
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186 views

How to add a low pass filter to this non-inverting amplifier circuit?

I've come up with this simple circuit as an amplifier before an 8bit ADC which receives audio signals. R2 is actually a variable resistor (pot.) of 100k. The circuit also biases the signal to VCC/2 ...
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2answers
52 views

Is a transfer function with a denominator of one with V_o/V_i as the definition of the function?

I've been given this question for my electronics course and have gone through it. The question asks we construct a circuit with transfer function: $$G(\omega) = 11 + j\omega 330 \times 10^{-6}$$The ...
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1answer
89 views

MP3301 LED Driver RC Filter Calculation for PWM

I am looking at the datasheet for the MPS MP3301 Step-up LED Driver. I have two questions about the "PWM Dimming" section on page 8. The datasheet says for PWM frequencies > 1kHz, use an RC filter ...
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1answer
87 views

Placement of RC filter used for slew rate limiting (for EMC)

I've seen RC combinations used on many circuits now which i believe have been included for slew rate limiting. They usually feed off to a connector. Do the placement of these matter in the circuit? ...
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1answer
119 views

RC Frequency to Voltage Converter

I'm an electronics engineering student and I want to state that this question is not my homework, it is a tiny part of my project (PWM encoder) but I couldn't pass it. I'm trying to make a "frequency ...