# Questions tagged [filter]

A filter selectively processes input signals in frequency- or time-domain.

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526 views

### Trouble with filter using Laplace transfer function in LTSpice

I would like to introduce an ideal 5th-order Bessel filter to my simulation. My initial thought is to use a voltage-dependent voltage source and Laplace transform. I copied the Bessel filter ...
143 views

### Find resistors for an inverting op amp band pass filter

I'm trying to save a problem that shows the following band pass filter: Note: the op amp doesn't need to be a TL081, it's an abstract, ideal op amp. I need to find resistors $R1$ and $R2$ so that ...
74 views

### Why would a low-pass filter be connected to +5V on an RS422 differential line?

I am interested in a datasheet's schematic for my own PCB design of a similar system. In my system, I am receiving an RS-422 differential line, and would simply be tempted to put a 100 Ohm terminating ...
205 views

### How does a PLL PFD produce a high frequency?

I am going to work with a PLL and a VCO. I have read and understood the basic procedure in which the charge pump works. I understood that say, when the reference signal (or the divided signal) is up ...
749 views

### RLC bandpass filter transfer function

I've been tasked with finding the transfer function of the RLC filter shown below. I converted to the S-domain and used the voltage divider rule to find the output, and came up with: H(s) = \frac{R}{...
41 views

### How do you chain 2-port S-parameters onto a 1-port S-parameter?

With 2-port S-parameters, you can build up a circuit by chaining them together using ABCD or T-parameters, simply multiply the matrices: We have measured a complex single port S-parameter of an ...
424 views

### GPIO input state with undefined voltage

I am using PIC32MX350 series controller, on one GPIO , that is defined as input , and input that pin goes form one SMPS (PN : - PSC35 , IO Name :- AC out). Since SMPS IO is open drain we add a pull up ...
1 vote
341 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 ...
614 views

### How to calculate voltage ripple in a BLDC filter module?

Hi I need some calculation for my thesis. A found this picture on the internet. My project is almost the same. It's a pi filter for a 3 phase BLDC. The peak current is 60A. It runs from 12V car ...
10k views

### The Cutoff frequency of bandpass filter

Given: Center Frequency f0 = 2.2KHz Q factor = 5 The problem I'm facing is this: How do I calculate the 2 cutoff frequencies of this band pass filter? I'm confused because my question says "The ...
1 vote
371 views

### Realization of network function and positive real function

I just studied 'network realizibility theory' from 'Franklin F.kuo's ' book and it mainly talks about postive real functions from start to finish and to me what I understand that for a function to be ...
53 views

### Do I need to add a filter for an isolated DC-DC converter?

I have purchased three CUI Isolated DC-DC Converters, the models are VHK50W-Q24-S5, VHK150W-Q24-S12 and VFK600-D24-S24. I wonder you could help / guide me to the correct use of them. Questions: I saw ...
112 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 ...
150 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 ...
54 views

### How can I calculate the parameters of an inverse Chebyshev active filter?

I'm currently designing an inverse Chebyshev 7th order low-pass filter with three 2nd-order low-pass notches and an RC low-pass filter. I've already used Simulink to obtain the s-domain transfer ...
152 views

### How to filter a noisy PWM signal without affecting rise and fall times

I need to read the frequency and duty cycle of a PWM signal that is expected at 88Hz. It is getting a lot of noise (during radiated immunity). Before noise: After noise injected: What filter would ...
228 views

### How to calculate cut-off frequency of an RC High Pass filter with two resistors?

Please consider the attached circuit. How would I calculate the cut-off frequency here? Should I treat resistors as attached in parallel? This is an actual circuit of an existing device, I cannot ...
1 vote
107 views

### Bandpass Amplifier

This is my frequency response , the point is if i change the capacitor values C1 and C4 my signal distorts on the second lobe in time domain and gain curve is not flat in the range. MY bandwidth is in ...
1 vote
46 views

### Discrepancy Between Bode Plot Predictions and FFT Output for Higher-Order Low Pass Filters on a 10 kHz Square Wave

I have conducted an experiment where a 10 kHz square wave is input through low pass filters of 1st, 2nd, 3rd, and 4th orders. After passing the square wave through these filters, I observed the FFT (...
1 vote
72 views

### Transistor specs in the capacitance multiplier

I'm working on a constant current power supply and as a first step designed the following rectifier with a filter. I know the bottom rectifier is inactive, but with couple of switches the circuit ...
199 views

### How does this phase advance loop filter work?

I am reading this paper titled A Versatile Digital GHz Phase Lock for External Cavity Diode Lasers. This is part of the circuit. I am confused about the functionality of the part labeled "Phase ...
1 vote
76 views

### Input Filter for Current Sense Amplifier - ODrive

Out of curiosity, can anyone explain to me why the input filters for the current sense amplifiers in the old ODrive schematics are unbalanced (i.e., the external resistor is only on the negative CSA ...
367 views

### Butterworth filter damping

A Butterworth filter has a damping ratio of 0.707 and is critically damped, but in general a damping ratio of 1 is critically damped, what is the theory behind this?
1 vote
77 views

### Butterworth filter

In filters, Butterworth filter is maximum flat response in pass band and Bessel filter have also flat response then what is the different between them. And how we can choose these filters in practical ...
132 views

### 2nd Order Butterworth filter design. How to find "m" and "n" values

I was reading this article Active-Low Passfilter design from Texas Instruments, and I've been racking my brain all day trying to find how they determine the values for "m" and "n" ...
1 vote
73 views

### Incorrect cutoff frequency using two Sallen-Key filters to build a bandstop filter

I'm currently having trouble troubleshooting my answer. I have to make a bandstop filter that has a cutoff frequency of 100 rad/s, and 10^6 rad/s using two Sallen-Key filters. I made the low and high ...
1 vote
1k views

### Input filter on differential amplifier input

Hi, I need to determine the transfer function Vout/Vin. A traditional differential amplifier transfer function without the 2.2uF on the input side would be G1 = (Z2/Z1)*Vin, where Z2 = (2.2uF // ...
1 vote
123 views

### Does this look like a correct Bandpass filter?

A project task assigned me to make a simple series RLC bandpass filter with values B = 73kHz & freq center = 4.8MHz known. I use equations B=R/L and fc=1/(2pisqrt(LC)) to get the RLC values. ...
342 views

I have quite simple question about topology of superheterodyne. I am facing with adjacent channel selectivity problem. The problem is that I can't obtain selectivity more than 40 dB. F.e. when wanted ...
47 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 ...
722 views

### Minimizing signal delay when debouncing

I have a mechanical switch that I'd like to use as a signal source for a digital input of a microcontroller. The switch is normally closed, and I'd like to detect the switch being opened as quickly as ...
87 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
39 views

### Switch Mode Power Supply / GPS - Filtering+Shielding

I'm working on my first RF PCB, for GPS/ GNSS and am particularly concerned about Noise/ Interference. Hopefully someone can shed some light, or point me toward a similar thread? It's worth noting ...
280 views

### Simple circuit question: nodal analysis

"simple circuit" I'm trying to find vout as a function of v1,r,c, and v2, but I'm i'm kind of stuck on what to do. I'm pretty sure you need to do nodal analysis, but I've never really encountered a ...
760 views

### Crystal filter impedance matching

I have a quite basic question about crystal filter impedance termination. F.e. ECS-45K20A 45Mhz IF filter - it has specified terminating impedance 910 Ohm / 2.5p. https://pl.mouser.com/datasheet/2/...
41 views

### STM32F0 VDD / VDDA connected

I want to use an STM32F0x to interface a i2c sensor via USB. Reading the sensor is triggered by an interrupt. If I don't do any ADC I should be fine with connecting VDD and VDDA right? I know this ...
52 views

### Why is Voltage Drop Across the Inductors of an LLCL Filter a Concern for Grid-Tied Inverters?

I'm working with a single-phase grid-tied inverter that utilizes an LLCL filter to interface with the grid. I've come across design constraints that mention maintaining the voltage drop across the ...
63 views

### AC power line filter no load current consumption

Our device is an induction cooktop rated for 2 kW of power. We have added an AC line filter in series with the AC supply line for EMI/EMC performance. Following is the circuit which we have ...
54 views

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 $\... 8 votes 3 answers 2k views ### How are RF filters constructed? I want to know what filter circuits look like in the RF (MHz-GHz) frequency range. Are they just like low frequency LC filters, but with appropriately adjusted component values? For example the VLF-80+... 3 votes 3 answers 708 views ### Finding the transfer function of an op-amp filter circuit I have the following third-order filter circuit: simulate this circuit – Schematic created using CircuitLab And I know that the transfer function looks like: \mathscr{H}\left(\text{s}\right)=\... 0 votes 0 answers 45 views ### 230 VAC 16 A relay Circuit for Reduced EMI I am designing a PCB that will needs EMI testing from a laboratory. I have a 230 VAC 16 A relay in PCB. I am not sure will it cause EMI issues while switching between loads or not. If anyone as better ... 0 votes 1 answer 66 views ### Problems with output signal of a 2nd order low pass Sallen Key filter for an electret microphone I'm having problems with a small circuit based on the amplification of a audio signal received by an electret microphone. It goes to a 2nd order Sallen Key low pass filter circuit with an ... 0 votes 1 answer 66 views ### In Bode plots what does phase tell us for passive filters (open loop)? I was just playing around with a passive filter to erase some noise - one that should work between 80MHz and 1GHz. I'm aware that the phase in Bode plots gives data about the time delay between the ... 1 vote 1 answer 314 views ### Given S-Parameters (or Y,Z,T,ABCD), how can you calculate$Q_C$and$Q_L\\$ (or, how do you calculate ESR)?

Background I'm writing a .s2p/Touchstone library for Perl and I'm trying to get the Q value of a component given an S-parameter matrix. The Goal In this case I'm trying to get Q for a 10nF muRata ...
202 views

### Does every transfer function in a circuit have its own resonant frequency?

When I studied the resonant frequency of an RLC circuit in series and parallel, there was the definition that I read in books that the imaginary part of the total impedance of the circuit has to be ...
1 vote
470 views

### Determine the impulse response of the following discrete system

I'm not sure how they got the answer (provided below) for the following discrete system y[n] = x[n]- 2x[n-2]+ x[n-3]- 3x[n-4] the answer is given as .... h[n] = [1 0 -2 1 -3] why is this? any help ...
50 views

### How to eliminate the VFD noise affecting digital sensor reading?

I have a problem getting correct readings from a 5v digital sensor connected to an Arduino Uno board. I get correct reading until I start the VFD that drives a 3-phase motor. The sensor reading then ...