
Home  Forums  Rules  Articles  diyAudio Store  Gallery  Wiki  Blogs  Register  Donations  FAQ  Calendar  Search  Today's Posts  Mark Forums Read  Search 
Solid State Talk all about solid state amplification. 

Please consider donating to help us continue to serve you.
Ads on/off / Custom Title / More PMs / More album space / Advanced printing & mass image saving 

Thread Tools  Search this Thread 
8th December 2010, 12:50 PM  #1 
diyAudio Member
Join Date: Dec 2010

non inverting op amp input impedance help
i have been given the task of designing an non inverting op amp, the criteria is
gain of 2 and input impedance of 9 if anyone can help me out in how it should look and what is the best way to design it. the op amp i designed i was told by a freind it was wrong so i am here to see if anyone can help p.s. i am new to this forum so apologise if i have posted in the wrong place. 
8th December 2010, 01:05 PM  #2 
diyAudio Moderator

Is this a class homework assignment? If not, what is this amp supposed to be doing? What's the function in the device in which it's used? 9 what?
I'm moving the question over to a more appropriate place.
__________________
“Just as soon as we get our opposable thumbs on an interesting concept, the rest of our chimp brains hijack it for a drunken joyride down the interstate.” 
8th December 2010, 01:15 PM  #3 
diyAudio Member
Join Date: Jul 2004
Location: Scottish Borders

Hi,
look up Wiki or other site and find out what inverting and non inverting schematics look like. Find out what unity gain stable means. Find out how to set the gain of an opamp circuit. Find out what determines the input impedance of an opamp gain block. Download the datasheet of a few "old" opamps. ne5534, tl071, lm353 etc. Look at the schematics for what you need and then alter to meet your assignment specification.
__________________
regards Andrew T. Sent from my desktop computer using a keyboard 
8th December 2010, 03:58 PM  #4 
diyAudio Member
Join Date: Nov 2010
Location: Milan

Sure is open loop?
First of all, In my way of understanding, NonInv depends on the topology of connection, not on the device. The same about the gain and the IN impedance, if we are speaking about CLOSEDLOOP (i.e. circuit, amplifier, NOT device). So design or use ANY High Open loop gain amplifier with differntial imput (i.e. o.l. gain =1000).
With such premises, you need to put a feedback resistor EQUAL to input resistor, so your gain will be Vg=1+ Rf/Ri=2. I hope it helps effebi 
8th December 2010, 06:00 PM  #5 
diyAudio Member
Join Date: May 2007

It might save time if your tutor posted the actual question here, then told all his students to simply copy our answer. Not good for education, but great for gaining marks. We could split the teaching fee among ourselves, or donate it to the website.

8th December 2010, 06:11 PM  #6 
diyAudio Member
Join Date: Nov 2010
Location: N.E. PA

In a noninverting configuration, the input impedance is a function of the input bias current. In even cheap opamps, this impedance is typically >1000 megohms. Very, very high. In most configurations it is desirable to have an established impedance, for signal matching, or to reduce stray current noise or other effects (in other circuits it is desirable to have very high impedances to not load certain sources). A simple resistor, or the desired impedance value, can be simply connected from the noninverting input in order to establish the desired value.
paul 
Thread Tools  Search this Thread 


Similar Threads  
Thread  Thread Starter  Forum  Replies  Last Post 
Inverting op amp out of phase?  RobertE  Analog Line Level  10  2nd December 2010 07:12 PM 
inverting / noninverting opamp circuits  Learnincurve  Solid State  11  21st January 2005 05:40 PM 
Input impedance of a noninverting op amp?  glennb  Chip Amps  24  21st May 2004 03:24 AM 
Inverting/noninverting Opamp Inputs !!!help!!!  IIR  Solid State  17  11th May 2002 02:02 AM 
New To Site?  Need Help? 