Input impedance of inverting stage of TPA6120? - diyAudio
 Input impedance of inverting stage of TPA6120?
 User Name Stay logged in? Password
 Home Forums Rules Articles diyAudio Store Gallery Wiki Blogs Register Donations FAQ Calendar Search Today's Posts Mark Forums Read Search

 Chip Amps Amplifiers based on integrated circuits

 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
 4th February 2012, 12:38 AM #1 diyAudio Member   Join Date: Jan 2012 Location: Rio de Janeiro Input impedance of inverting stage of TPA6120? I would like to find out TPA6120 built in the datasheet reference schematic "Single-Ended Input With a Noninverting Gain of -1 V/V" with Rl = 1k and Rf = 1k. It says the input resistance of TPA6120 is 300k, however, I am a bit confused because input resistance and input impedance are clearly different concepts. So I figured this should not be the input impedance of this chip. Also, in my past experience, I figure the input impedance of this stage is quite low. Has anyone measured this or know an equation to come up with this? Last edited by Mateo Jun; 4th February 2012 at 12:52 AM.
 4th February 2012, 01:21 AM #2 diyAudio Member     Join Date: Apr 2008 Location: Carlisle, England If the audio goes in on the + input then the input impedance is 300K. If the audio goes in on the - input it will be the input resistor to the - input. __________________ Murton-Pike Systems PCBCAD51 pcb design software. http://www.murtonpikesystems.co.uk
diyAudio Member

Join Date: Jan 2012
Location: Rio de Janeiro
Quote:
 Originally Posted by nigelwright7557 If the audio goes in on the + input then the input impedance is 300K. If the audio goes in on the - input it will be the input resistor to the - input.
Thank you very much, Nigel!

 4th February 2012, 11:03 AM #4 diyAudio Member   Join Date: Jul 2004 Location: Scottish Borders Using the 1k & 1k around the inverting amp, you will probably need a source impedance <=51r. Aiming for ~10r might be better. __________________ regards Andrew T. Sent from my desktop computer using a keyboard
 4th February 2012, 12:14 PM #5 diyAudio Moderator     Join Date: Sep 2007 The data sheet says it's a current feedback (CFA) type opamp so that is one reason why the resistor values are low. You need to keep to that and use a suitable driver before this device. The inverting and non inverting input impedances are very very different on a CFA amp as far as I know. Non inverting input is normally high impedance and inverting is low impedance. Looks a very interesting device though
 4th February 2012, 01:44 PM #6 diyAudio Member     Join Date: Jul 2003 Location: Cambridge UK If you haven't used current feedback amplifiers before, be sure to take notice of the feedback resistor value requirements. If you have reasonable math and some electronics this is a good description. You can treat the positive input much like you would a voltage amplifier. The negative input needs the correct resistance feedback resistor to remain stable and you must ensure parasitic capacitance is minimised. So it it's on a plane you may need a guard ring to isolate the input from the plane capacitance or to relive the plane in that region. http://cas.ee.ic.ac.uk/people/dario/...cf-sloa080.pdf Regards, Andy

 Posting Rules You may not post new threads You may not post replies You may not post attachments You may not edit your posts BB code is On Smilies are On [IMG] code is On HTML code is OffTrackbacks are Off Pingbacks are Off Refbacks are Off Forum Rules

 Similar Threads Thread Thread Starter Forum Replies Last Post sirus the virus Solid State 5 8th December 2010 06:11 PM mahleriana Tubes / Valves 0 16th November 2009 09:37 PM zox2003 Class D 1 1st February 2008 07:48 AM mr.duck Chip Amps 11 12th January 2007 10:46 AM glennb Chip Amps 24 21st May 2004 03:24 AM

 New To Site? Need Help?

All times are GMT. The time now is 09:51 AM.