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Digital Filter Design for ECE Students

The document describes an ECE 626 project involving analog filter design. It involves: 1. Designing a 2nd order low-pass Butterworth filter with a 5MHz cutoff frequency in the continuous time domain. 2. Transforming the filter to the discrete time domain using impulse invariance with a sample rate of 10MHz. 3. Observing the discrete time filter characteristics using Bode plots and pole-zero plots in MATLAB. 4. Converting the discrete time transfer function to a fully differential switched-capacitor circuit implementation and simulating the frequency response in Cadence.

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Manoj Medigeshi raghu
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85 views16 pages

Digital Filter Design for ECE Students

The document describes an ECE 626 project involving analog filter design. It involves: 1. Designing a 2nd order low-pass Butterworth filter with a 5MHz cutoff frequency in the continuous time domain. 2. Transforming the filter to the discrete time domain using impulse invariance with a sample rate of 10MHz. 3. Observing the discrete time filter characteristics using Bode plots and pole-zero plots in MATLAB. 4. Converting the discrete time transfer function to a fully differential switched-capacitor circuit implementation and simulating the frequency response in Cadence.

Uploaded by

Manoj Medigeshi raghu
Copyright
© © All Rights Reserved
We take content rights seriously. If you suspect this is your content, claim it here.
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Download as PDF, TXT or read online on Scribd
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ECE 626 Project

Rishi Gupta
School of Electrical Engineering and
Computer Science
Oregon State University
Matlab
Fs=10MHz
DC gain=0db
Fp=0~1MHz
1. Declare and analog filter. I set the cutoff to 5MHz (random choice).

[num,den]=butter(2,5e6,'low','s');
H=tf(num,den)
bode(H);

2. Transfrom to z-domain using impulse invariance method.

[numz,denz]=impinvar(num,den,10e6);
Hz=tf(numz,denz,100e-9)

3. Observe the discrete time charecteristics. Fvtool plots everything, I’ve olny
shown magnitude response and pole zero plot.

hz=fvtool(numz,denz);
Magnitude Response
Normalized Frequency: 0 Magnitude Response (dB)
0.5425
Magnitude (dB): -0.182093

-2.1581

-4.8588

-7.5594

-10.26
Magnitude (dB)

-12.9606

-15.6612

-18.3618

-21.0624

-23.7631

-26.4637
0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9
Normalized Frequency (  rad/sample)
Pole-Zero Plot
Pole/Zero Plot
1.0997

0.8798

0.6598

0.4399

0.2199
Imaginary Part

-0.2199

-0.4399

-0.6598

-0.8798

-1.0997
-1.5 -1 -0.5 0 0.5 1 1.5 2
Real Part
Converting TF to circuit.
Transfer function:
0.1719 z
Hz= ---------------------------
z^2 - 1.318 z + 0.4931

Sampling time: 1e-007

* Refer to page 418 of Johns Martin on how to do this, DO NOT BLINDLY


GET THE COIFICENTS. Work it out yourself to make sure.
The Fully Differential Circuit
Making an Ideal Switch
• analogLib-> switch (relay line)

• Set a threshold of VDD/2

• Bypass cap added to aid with


convergence.
Making an Ideal OPAMP
• analogLib-> dependant sources -> vcvs
Simulating the Frequency Response
• Click on the vsource and set all
the options.
Simulating the Frequency Response
• Go to the Analog enviorment.
Simulating the Frequency Response
• Set the PAC analysis like the following.

• Make sure the stop frequency is Fs/2


Simulating the Frequency Response
• From the Analog Enviorment click on
AC TRAN DC Button, and pick PSS

• And follow this. Make sure your phi1


and phi2 show up. The will be at your
sampling frequency.

• Always select conservative for most


accurate results.
Simulating the Frequency Response
• Make sure your PSS window looks like this.
Simulating the Frequency Response
• Change to the PAC option.

• Under select make sure you change it to differential


Simulating the Frequency Response
Simulating the Frequency Response

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