OP-AMP output impedance

hugeli60 · 19th February 2004, 01:03 PM

Is there any way to effectively decrease the output impedance of an op-amp in voltage follower mode. (THis is small signal stuff, +/- 15v rails). I have an application that requires Zout to be less than .001 ohm.

Any Suggestions?

janneman · 19th February 2004, 01:07 PM

I think that with carefull selection of the opamp, there are some out there that will provide this as-is. What is the freq range over which you want it to be .001? What is the required output current? Just curious, what is the application?

Also, be aware that this will be completely swamped by PCB-trace and wiring impedance, UNLESS you take your feedback point directly from the load.

Jan Didden

peranders · 19th February 2004, 02:14 PM

Quote:

Originally posted by hugeli60
Is there any way to effectively decrease the output impedance of an op-amp in voltage follower mode. (THis is small signal stuff, +/- 15v rails). I have an application that requires Zout to be less than .001 ohm.

What are you up to, if I may ask?

ChocoHolic · 19th February 2004, 05:35 PM

Any idea how to set up the wiring in order to get this
low impedance not only at the at the output of the OP amp, but
also at that point were you need this low signal impedance.

May be you will have to put the signal wiring also "inside" the
feedback loop of the OP amp...
..and take care about your ground...
... real 1mOhm... let's say: a challenge

sreten · 19th February 2004, 05:39 PM

Usually a series resistor in thr output ensures
high frequency stability into capacitive loads.

The real issue here is your applications requirements.

Where do they come from, and is there a better way of doing it ?

Note that feedback derived output impedance varies strongly with frequency.

sreten.

dmfraser · 20th February 2004, 04:05 PM

Any op-amp will try to have a zero output impedance. However, if it it this scritical, it is essential to do a "Kelvin" connection. Both ends of the feedback path have to be across your load with the shortest possible connection. Also, do not ask the op-amp to behave as if it has such a low output impedance and to give a lot of output voltage. With a ±15V supply, expect that performance perhaps to only ±2V. That is unless you build an output power buffer.

As well, I hope the load impedance still won't be a lot less than a few hundred ohms. If lower, you're in a whole different class of product.

PMA · 20th February 2004, 05:56 PM

OpAmp's output impedance strongly depends on:

1) OpAmp type (i.e. circuit design)
2) closed loop gain
3) frequency

Consult datasheets, you will find answer there.

19th February 2004, 01:03 PM	#1
hugeli60 diyAudio Member Join Date: Jan 2002 Location: Williamsport, PA	OP-AMP output impedance Is there any way to effectively decrease the output impedance of an op-amp in voltage follower mode. (THis is small signal stuff, +/- 15v rails). I have an application that requires Zout to be less than .001 ohm. Any Suggestions?

20th February 2004, 04:05 PM	#6
dmfraser diyAudio Member Join Date: Dec 2003 Location: Orange County, CA	Fedback Point Any op-amp will try to have a zero output impedance. However, if it it this scritical, it is essential to do a "Kelvin" connection. Both ends of the feedback path have to be across your load with the shortest possible connection. Also, do not ask the op-amp to behave as if it has such a low output impedance and to give a lot of output voltage. With a ±15V supply, expect that performance perhaps to only ±2V. That is unless you build an output power buffer. As well, I hope the load impedance still won't be a lot less than a few hundred ohms. If lower, you're in a whole different class of product. __________________ Dan Fraser

Thread Tools	Search this Thread
Show Printable Version Email this Page	Search this Thread: Advanced Search

Similar Threads
Thread	Thread Starter	Forum	Replies	Last Post
3C24 in a SE output stage - output transformer impedance recommendation !!!	aldovan	Tubes / Valves	15	6th September 2008 10:18 AM
Output impedance	overdrajv	Tubes / Valves	8	5th March 2008 05:54 PM
Can An Output Transformer Change A Voltage Amp's Output Impedance From 0.1 To 47 Ohms	kelticwizard	Everything Else	11	25th March 2007 05:17 AM
Output Impedance?	ble0t	Parts	4	19th January 2006 05:45 PM
Low output impedance pre	miguel2	Tubes / Valves	13	23rd July 2003 09:51 AM

New To Site?	Need Help?
Register to Participate Search Privacy Statement Contact Us	Frequently Asked Questions Did you forget your password? Mark Forums Read


	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

19th February 2004, 01:07 PM	#2
janneman diyAudio Member Join Date: May 2002 Location: Where Germany, The Netherlands and Belgium meet Blog Entries: 6	I think that with carefull selection of the opamp, there are some out there that will provide this as-is. What is the freq range over which you want it to be .001? What is the required output current? Just curious, what is the application? Also, be aware that this will be completely swamped by PCB-trace and wiring impedance, UNLESS you take your feedback point directly from the load. Jan Didden

19th February 2004, 05:35 PM	#4
ChocoHolic diyAudio Member Join Date: Dec 2003 Location: Munich	Any idea how to set up the wiring in order to get this low impedance not only at the at the output of the OP amp, but also at that point were you need this low signal impedance. May be you will have to put the signal wiring also "inside" the feedback loop of the OP amp... ..and take care about your ground... ... real 1mOhm... let's say: a challenge

19th February 2004, 05:39 PM	#5
sreten diyAudio Member Join Date: Nov 2003 Location: Brighton UK	Usually a series resistor in thr output ensures high frequency stability into capacitive loads. The real issue here is your applications requirements. Where do they come from, and is there a better way of doing it ? Note that feedback derived output impedance varies strongly with frequency. sreten.

20th February 2004, 05:56 PM	#7
PMA diyAudio Member Join Date: Apr 2002 Location: Prague, Kitakyushu, Fukuoka	OpAmp's output impedance strongly depends on: 1) OpAmp type (i.e. circuit design) 2) closed loop gain 3) frequency Consult datasheets, you will find answer there.

Currently Active Users Viewing This Thread: 1 (0 members and 1 guests)