# Tagged Questions

155 views

### Dedicated digital filter

I have built a DDS (0-80MHz) with an FPGA (XC3S400) that I can program it for making almost any wave form (limited frequency by the wave form complexity). After weeks of struggling with making a ...
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### 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 ...
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### How to Calculate Complex Low Pass Passive RLC Filters?

I have designed a FPGA based DDS and now I want to add a low pass filter to its output. Previously I was working on a project based on AD9850 DDS(0-50MHz) and I had a commercial module for it that had ...
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### What is the transfer function of n-cascaded RC filters?

Is there an explicit formulation for n-cascaded RC filters? The resistor and capacitor values are not necessarily same. Assume that: $R_i \neq R_j$ and $C_i \neq C_j$ for $i \neq j$ and ...
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### Why is there a lower limit on amplification for this filter design method?

I'm designing an active low-pass filter for a differential input. The input is on a ±100V scale and needs to be scaled down to the standard ±10V scale. I found this application note which describes ...
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### how to set rc passive low-pass filter?

I have got a analog signal that include some unwanted ac noise. the noise amount is about 0.5 mv. I want to use passive rc low-pass filter but i don't understand which frequency that i need to pass. ...
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### Confusion about filter transfer function

Today I got confused about Low pass filter transfer function. Let's assume we have a simple low pass RC filter . It is well known that at f=fc we expect -3dB (0.707) drop in Vin. Everyone knows a LPF ...
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### What are best values of a Low/High pass RC filter?

Cutoff frequency of a RC filer is obtained from well known equation: 1/(2 pi RC). This is one equation with 2 variables. for example R=100 , C=10 has the same result as R=10 , C=100. Which value is ...
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### Active low-pass butterworth filter design

I have a project on filtering out frequency above 2.5 KHz. The filter should be low pass butterworth. I am confused here as there are two cutoff frequencies I need to use. 1st cutoff freq. 1KHz and ...
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### Active low pass filter giving constant output regardless of input

I have a sensor that gives me an output between 1 and 4V, and I wanted to filter out noise present on the output to give me a more stable and accurate reading. I set up an active 2nd-order ...
350 views

### How to recognize the type of analog filter given its topology?

Having trouble to tell what kind of filter (Low-Pass, High-Pass, Band-Pass, Band-Reject(Notch) are present given a topology in cascade. In the following picture I see 3 stages, is this ok? (2 active ...
354 views

### Eliminate hiss and noise

ATTiny is generating PWM based tones with 32kHz sampling rate. Then I've created R-2R DAC and then trying to amplify it for the speaker. I need to make low pass RC filter, to cut PWM hiss during ...
452 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 ...
506 views

### Low Pass Filter Design [duplicate]

Possible Duplicate: Injecting a communication signal over DC power supply lines I have a pretty simple circuit, but I need to send an output PWM signal through the same place I'm getting my ...
987 views

### Filter Design with Opamps Query

While I was reading about filter design, and going through the schematics, the following 2 questions popped up in my mind and I could not find a satisfactory answer to them: 1) A first order low pass ...
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### Design a 1 GHz lowpass filter

I want to design a 1 GHz low-pass filter. I have tried to find a COTS lowpass filter at such high frequencies but I can't find one. Hence, I have decided to design one using microstrip lines. So, ...
711 views

### 100W Low Pass Filter

Currently I have a 60W amplifier for the 400-500MHZ band with a 50Ω impedance. In order to prevent jamming other frequencies I will need a low pass filter to block any frequencies above 500MHZ. I just ...