Welcome to EDAboard.com

Welcome to our site! EDAboard.com is an international Electronic Discussion Forum focused on EDA software, circuits, schematics, books, theory, papers, asic, pld, 8051, DSP, Network, RF, Analog Design, PCB, Service Manuals... and a whole lot more! To participate you need to register. Registration is free. Click here to register now.

Register Log in

Analog and Digital Filters, Pros and Cons

Status
Not open for further replies.

Saad mahsoub

Newbie level 4
Joined
Jul 15, 2012
Messages
7
Helped
0
Reputation
0
Reaction score
0
Trophy points
1,281
Activity points
1,337
I am interested in a simple comparison of analog & digital filters in general as to frequency response , hardware requirements, delay, limitations of both filters,....etc, and in general their pros and cons. I am much obliged if anyone can help me with this comparison or guide me to sources of such matter but rather simple detailed ones not the mathematical theory but only pros and cons and much of them.
Regards and many thanks
S. Mahsoub
 

th3gr8

Member level 4
Joined
Aug 27, 2013
Messages
68
Helped
6
Reputation
12
Reaction score
6
Trophy points
8
Activity points
398
1) Analog filters are designed with R, L and C where Digital filters are designed via coding ..
2) To change anything in Analog filter, whole design has to be changed whereas in Digital filters, you just need to change the code ..
3) Digital filters are more reliable and easy to design as compare to Analog filters ..
4) A high order Analog filter may get bulky whereas a high order Digital Filter doesn't get bulky as it is designed via code ..
5) Analog filters are much more affected by surrounding noise as compared to Digital Filters ..
 

Audioguru

Advanced Member level 5
Joined
Jan 19, 2008
Messages
9,167
Helped
2,119
Reputation
4,232
Reaction score
1,947
Trophy points
1,393
Location
Toronto area of Canada
Activity points
57,582
I have used a switched capacitor filter IC to make an excellent Butterworth lowpass filter and a notch filter. Is it analog or digital? I think it is digital.
 

Saad mahsoub

Newbie level 4
Joined
Jul 15, 2012
Messages
7
Helped
0
Reputation
0
Reaction score
0
Trophy points
1,281
Activity points
1,337
1) Analog filters are designed with R, L and C where Digital filters are designed via coding ..
2) To change anything in Analog filter, whole design has to be changed whereas in Digital filters, you just need to change the code ..
3) Digital filters are more reliable and easy to design as compare to Analog filters ..
4) A high order Analog filter may get bulky whereas a high order Digital Filter doesn't get bulky as it is designed via code ..
5) Analog filters are much more affected by surrounding noise as compared to Digital Filters ..
can you please elaborate more . do analog filters have merits over digital ones?
 

FvM

Super Moderator
Staff member
Joined
Jan 22, 2008
Messages
47,977
Helped
14,147
Reputation
28,553
Reaction score
12,834
Trophy points
1,393
Location
Bochum, Germany
Activity points
278,292
have used a switched capacitor filter IC to make an excellent Butterworth lowpass filter and a notch filter. Is it analog or digital? I think it is digital.
The example shows the need for a more precise discrimination. Digital filters involve both time and amplitude discrete signal processing. Signal processing in switched capacitor filters is time discrete and amplitude continuous. The latter feature qualifies it as analog. But because it's discrete time, the same z-domain calculation methods as for digital filters have to be applied.
 

LvW

Advanced Member level 5
Joined
May 7, 2008
Messages
5,835
Helped
1,740
Reputation
3,484
Reaction score
1,340
Trophy points
1,393
Location
Germany
Activity points
39,237
I have used a switched capacitor filter IC to make an excellent Butterworth lowpass filter and a notch filter. Is it analog or digital? I think it is digital.
I rather think that switched-capacitor filter are classified as "sampled data systems" - and as such they are "between" analog and digital filters ("time discrete and amplitude continuous " as explained by FvM).
Moreover, in response to the answer in post#2 I like to add that - as far as analog filters are concerned - we discriminate between two major classes: Passive RLC and active-RC.
 

andre_teprom

Super Moderator
Staff member
Joined
Nov 7, 2006
Messages
9,201
Helped
1,142
Reputation
2,303
Reaction score
1,119
Trophy points
1,403
Location
Brazil
Activity points
53,591
can you please elaborate more . do analog filters have merits over digital ones?
Digital filters are as precise as its clock rate can be, generaly few more than crystal oscillator near to 0,001%, differently from analog filters that are limited to the combination of multiple components precision, which idividually varies from 0,1% for resistors up to 2-5% for capacitors.

This fact ensures a better accuracy expected on digital filters rather than analog filters.
 

Saad mahsoub

Newbie level 4
Joined
Jul 15, 2012
Messages
7
Helped
0
Reputation
0
Reaction score
0
Trophy points
1,281
Activity points
1,337
Digital filters are as precise as its clock rate can be, generaly few more than crystal oscillator near to 0,001%, differently from analog filters that are limited to the combination of multiple components precision, which idividually varies from 0,1% for resistors up to 2-5% for capacitors.

This fact ensures a better accuracy expected on digital filters rather than analog filters.
Digital filters seem to be better than analog, but on what expense? what are the extra and actual requirements of digital filters?

- - - Updated - - -

To Saad Mahsoub:
Perhaps the following link can answer some of your questions:

http://complextoreal.com/wp-content/uploads/2013/01/filters.pdf
Thanks for your effort. I am reading the file now,it is good.
 

Saad mahsoub

Newbie level 4
Joined
Jul 15, 2012
Messages
7
Helped
0
Reputation
0
Reaction score
0
Trophy points
1,281
Activity points
1,337
I wish i can get a comparison table in a concise manner with points of comparison as to complexity & hardware requirements, stability, linearity in frequency and phase responses, limitations in hardware and probably software . I need to know the drawbacks and limitations of digital filters in general in particular.
 

andre_teprom

Super Moderator
Staff member
Joined
Nov 7, 2006
Messages
9,201
Helped
1,142
Reputation
2,303
Reaction score
1,119
Trophy points
1,403
Location
Brazil
Activity points
53,591
Except for the need to have a reasonable microcontroller system to accomplish the filtering digitally, I see no more drawbacks. For both Analog and Digital approaches, there are currently available lots of powerful tools which significantly reduces development time to somewhat negligible.
 

LvW

Advanced Member level 5
Joined
May 7, 2008
Messages
5,835
Helped
1,740
Reputation
3,484
Reaction score
1,340
Trophy points
1,393
Location
Germany
Activity points
39,237
Except for the need to have a reasonable microcontroller system to accomplish the filtering digitally, I see no more drawbacks.
In many many cases the signal to be filtered is analog.
In case of digital filtering techniques you need (a) analog prefiltering, (b) A-D converter, (c) the filter, (d) D-A converter, (e) analog post filtering.
 

andre_teprom

Super Moderator
Staff member
Joined
Nov 7, 2006
Messages
9,201
Helped
1,142
Reputation
2,303
Reaction score
1,119
Trophy points
1,403
Location
Brazil
Activity points
53,591
Stages (a) and (e) above are required for both implementations, either analog or digital. Furthermore, considering built-in hardware modules available on current microcontrolers ( particularly A/D and PWM ), the external conversion circuitry can be somewhat reduced.
 

LvW

Advanced Member level 5
Joined
May 7, 2008
Messages
5,835
Helped
1,740
Reputation
3,484
Reaction score
1,340
Trophy points
1,393
Location
Germany
Activity points
39,237
Stages (a) and (e) above are required for both implementations, either analog or digital

Pre- and post filtering also for analog???
 

andre_teprom

Super Moderator
Staff member
Joined
Nov 7, 2006
Messages
9,201
Helped
1,142
Reputation
2,303
Reaction score
1,119
Trophy points
1,403
Location
Brazil
Activity points
53,591
You´re right, I guess you was referring to the pre filtering process mentioned above as the pre conditioning for the signal. Anyway, returning to the original question, I would not properly consider these steps as issues, once done digitally stays on the programming scope, and no additional cost is accounted due to the extra core processing.
 

Saad mahsoub

Newbie level 4
Joined
Jul 15, 2012
Messages
7
Helped
0
Reputation
0
Reaction score
0
Trophy points
1,281
Activity points
1,337
Thanks for your comments. One thing I forgot to ask, is what are the points that I should consider when comparing the two filters? I know of linearity, phase response, steepness between cut and pass ranges. If you can, please suggest others.
Thanks.
 

betwixt

Super Moderator
Staff member
Joined
Jul 4, 2009
Messages
14,715
Helped
4,810
Reputation
9,637
Reaction score
4,590
Trophy points
1,393
Location
Aberdyfi, West Wales, UK
Activity points
125,344
Nobody has mentioned the upper frequency limitations of digital filters. To process in the digital domain requires a system capable of multiple calculations within the wavelength of the signal, analog does not. Although there is no technical limit to the upper frequency of digital filters, it is decided by the speed the calculations can be performed and hence currently available technology. At the moment, low VHF is about as good as it gets but analog networks can continue to filter effectively well into microwave frequencies.

Brian.
 

LvW

Advanced Member level 5
Joined
May 7, 2008
Messages
5,835
Helped
1,740
Reputation
3,484
Reaction score
1,340
Trophy points
1,393
Location
Germany
Activity points
39,237
For my opinion - such a comparison makes not too much sense. Why?
It´s hard to imagine that in case of signal processing in the analog world (input and output signals of the filter pure analog) somebody decides to replace an analog filter with a digital one. What should he gain? The circuitry certainly will be more complex (in an ealier post I already have mentioned the necessity of analog pre- and post-filtering). However - if continuous tuning of the pole frequecy is desired (what is problematic for pure analog) there is one technology just "between" analog and digital: Switched capacitor filters.
 

andre_teprom

Super Moderator
Staff member
Joined
Nov 7, 2006
Messages
9,201
Helped
1,142
Reputation
2,303
Reaction score
1,119
Trophy points
1,403
Location
Brazil
Activity points
53,591
For filters having critical requirements with respect to the accurate location of poles and zeros, I fear switched capacitor filters can be a problem due to the inherent inaccuracy in characterizing the value of a capacitor implemented in silicon, or even external.

In fact, for each application one or other implementation could be the more appropriate.
 

Audioguru

Advanced Member level 5
Joined
Jan 19, 2008
Messages
9,167
Helped
2,119
Reputation
4,232
Reaction score
1,947
Trophy points
1,393
Location
Toronto area of Canada
Activity points
57,582
The switched capacitor Butterworth lowpass and notch filter ICs I have used (from National Semiconductor) were very accurate. Their frequency is tuned by changing the clock frequency.
 

Status
Not open for further replies.

Part and Inventory Search

Welcome to EDABoard.com

Sponsor

Top