1. Test! OpAmp Active Filters

2. Q. What is v0?

3. Filter What is Active filter? What is Passive filter?
What is analog filter?
What is digital filter?
An analog filter processes continuous-time signals
A digital filter processes discrete-time signals

4. What is filter?
Purpose of filter?
Types of filters?
What is cut-off frequency?
Draw frequency responses of 4 filters?
What is pass-band?

5. Pros and cons of active filter?
Pros and cons of passive filter?

6. EE3110 Active Filter (Part 1)
Passive Filters
made up of passive components - resistors, capacitors and inductors
no amplifying elements (- transistors, op-amps, etc)
no signal gain
1st order - design is simple (just use standard equations to find resonant frequency of the circuit)
2nd order - complex equations
require no power supplies
not restricted by the bandwidth limitations of the op-amps
can be used at very high frequencies
can handle larger current or voltage levels than active devices
They are particularly non-ideal (lossy)
They are bulky and expensive
Ref:080222HKN
EE3110 Active Filter (Part 1)

7. Passive elements : Inductor
high accuracy (1% or 2%), small physical size, or large inductance values are required??
standard values of inductors are not very closely spaced
difficult to find an off-the-shelf inductor within 10 percent of any arbitrary value
adjustable inductors are used
tuning such inductors to the required values is time-consuming and expensive for larger quantities of filters
inductors are often prohibitively expensive
EE3110 Active Filter (Part 1)

8. EE3110 Active Filter (Part 1)
no inductors
made up of op-amps, resistors and capacitors
provides virtually any arbitrary gain
generally easier to design
high input impedance prevents excessive loading of the driving source
low output impedance prevents the filter from being affected by the load
at high frequencies is limited by the gain-bandwidth of the op-amps
easy to adjust over a wide frequency range without altering the desired response
Ref:080222HKN
EE3110 Active Filter (Part 1)

9. Draw ideal filter responses of 4 types of filters.
Draw the same for practical filters.

10. Draw the Bessel characteristics of a LPF.
Draw the same for a HPF.

11. Bessel Characteristic
Flat response in the passband.
Phase response is linear.
Used for filtering pulse waveforms without distorting the shape of the waveform.
Ref:080222HKN
EE3110 Active Filter (Part 1)

12. Draw Butterworth characteristic for HPF.

13. Butterworth Characteristic
Very flat amplitude, Av(dB) , response in the passband.
Phase response is not linear.
Used when all frequencies in the passband must have the same gain.
Often referred to as a maximally flat response.
Ref:080222HKN
EE3110 Active Filter (Part 1)

14. Draw Chebyshev characteristic for LPF
Draw the same for BPF

15. Chebyshev Characteristic
Overshoot or ripples in the passband.
Role-off rate greater than 20dB/decade/pole.
Phase response is not linear - worse than Butterworth.
Used when a rapid roll-off is required.
Ref:080222HKN
EE3110 Active Filter (Part 1)

16. Draw a passive LPF filter circuit.
Draw an active LPF filter circuit.

17. Passive LPF

18. Active LPF using OpAmp

19. What is cut-off frequency for LPF?
What is ,,, for HPF?
What is ,,, for BPF?
What is ,,, for BRF?

21. What is dB/decade?

22. dB/…
In many situations, the magnitude attenuation of a signal is given in units of dB/decade or dB/octave.
The decibel is defined in terms of a power (P) ratio, or the magnitude ratio (M).
A decade is defined as a 10-fold increase in frequency.
An octave is defined as a 2-fold increase (doubling) in frequency.

23. How can we improve the performance of a filter?

24. Better response? 2nd order?

25. Draw a circuit for active HPF.

26. HPF

27. Draw a circuit for 2nd order HPF.

28. 2nd order HPF

29. Draw a circuit for BPF.

30. Two-Stage Band-Pass Filter
BW = f2 – f1
Q = f0 / BW
Ref:080222HKN
EE3110 Active Filter (Part 1)

31. Draw a model for BRF, BSF, BEF, notch filter.

32. Band-Stop (Notch) Filter
The notch filter is designed to block all frequencies that fall within its bandwidth. The circuit is made up of a high pass filter, a low-pass filter and a summing amplifier. The summing amplifier will have an output that is equal to the sum of the filter output voltages.
Block diagram
Frequency response
Ref:080222HKN
EE3110 Active Filter (Part 1)

33. EE3110 Active Filter (Part 1)
Notch filter
Ref:080222HKN
EE3110 Active Filter (Part 1)