Continue to Site

Welcome to EDAboard.com

Welcome to our site! EDAboard.com is an international Electronics 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

Need a review of a Front-End Circuit for an A2D Converter

Status
Not open for further replies.
P

ProEngineer

Junior Member level 3
Joined
Jan 19, 2010
Messages
28
Helped
2
Reputation
4
Reaction score
0
Trophy points
1,281
Location
USA
Activity points
1,453
I have a project that is basically a Spectrum Analyzer that needs to accept in input from 5 to 600VAC (RMS). The front-end needs to be auto-ranging and include a low-pass filter (DC to 3KHz). The attached file is my proposed circuit. Before I commit it to a PCB, I'd appreciate it if some of you review it and comment.

Some Notes:
- RL1 through RL8 are relay contacts; the coils will be driven by a uP
- The Diodes are there to clamp the input to the Op Amp
- The sum of R1 through R8 will be 500K, giving me a 1M input impedence
 

Hi,
In my opinion is some logically wrong: for me are the ranges 5V...1KV rotated!
I mean- for 1KV on the input must RL1 not between R10&R1, but correcter R7&R8 be; and so on...
These because you need the highest attenuation with 1KV on the input.
K.
 
Yep, you're absolutely right about that!
 

:)
Your welcome & tnx!
Good luck!
K.
 

Re: Need a review of a Front-End Circuit for an A2D Converte

ProEngineer said:
Nobody else have any comments?
Click to expand...

You could save on the number of relays if you wanted by having two stages e.g. 3 relays followed by 3 more relays.

You filter looks strange, but maybe it's just a configuration I am not familiar with. Normally I would expect C2 to be on the opamp input, R11 to be a capacitor and C1 to be a resistor.

Keith.
 

Re: Need a review of a Front-End Circuit for an A2D Converte

keith1200rs said:
You could save on the number of relays if you wanted by having two stages e.g. 3 relays followed by 3 more relays.
Click to expand...
Yes you are right, but I'm driving the relays using a 3-to-8 line decoder to reduce the pin count on the uP.

keith1200rs said:
You filter looks strange, but maybe it's just a configuration I am not familiar with. Normally I would expect C2 to be on the opamp input, R11 to be a capacitor and C1 to be a resistor.
Click to expand...
My circuit is a low-pass filter, I believe what you are describing is a band-pass configuration.
 

Re: Need a review of a Front-End Circuit for an A2D Converte

ProEngineer said:
keith1200rs said:
You filter looks strange, but maybe it's just a configuration I am not familiar with. Normally I would expect C2 to be on the opamp input, R11 to be a capacitor and C1 to be a resistor.
Click to expand...
My circuit is a low-pass filter, I believe what you are describing is a band-pass configuration.
Click to expand...

No, I am definitely thinking of a low pass filter design, but maybe it is just different to yours:

https://en.wikipedia.org/wiki/File:Sallen-Key_Lowpass_General.svg

Keith.
 

Re: Need a review of a Front-End Circuit for an A2D Converte

keith1200rs said:
No, I am definitely thinking of a low pass filter design, but maybe it is just different to yours: https://en.wikipedia.org/wiki/File:Sallen-Key_Lowpass_General.svg
Keith.
Click to expand...
Ok, I see...yours is a Sallen-Key topology while mine is a Multiple-Feedback. I don't know if one is better than the other for this application. Maybe one of the Analog Experts will chime in here.
 

Re: Need a review of a Front-End Circuit for an A2D Converte

ProEngineer said:
Ok, I see...yours is a Sallen-Key topology while mine is a Multiple-Feedback. I don't know if one is better than the other for this application. Maybe one of the Analog Experts will chime in here.
Click to expand...

I think the fact that Sallen-Key is non-inverting and Multiple Feedback is inverting is the main difference. Both can have gain.

Keith.
 

Status
Not open for further replies.

Similar threads

Part and Inventory Search

Welcome to EDABoard.com

Sponsor

Back
Top