How to plot open-loop gain for single-transistor-input feedback amplifier?
 User Name Stay logged in? Password
 Home Forums Rules Articles diyAudio Store Blogs Gallery Wiki 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
steveh49
diyAudio Member

Join Date: Feb 2003
Location: Australia
How to plot open-loop gain for single-transistor-input feedback amplifier?

I'm trying to plot the open-loop gain of a single-transistor-input circuit in SPICE, without using a loop-gain probe or similar. To explain it better, I've shown what I want to do in the first two attached pictures, but for a diff-pair input. In the left diff-pair circuit, I've set it up to run open loop using a large inductor and capacitor in the feedback network. The open-loop gain is 72dB (Q3 current gain = 165) and gain-bandwidth is 1MHz (blue line on the graph). The right-hand diff-pair circuit is operating with feedback but I can still plot the open-loop gain as output divided by differential input voltage (green line, identical to blue line).

I want to do the same thing for a single-transistor-input circuit. The third attachment shows the circuit. Again, I have the left circuit operating open-loop and it has 55dB open-loop gain (Q2 current gain = 210) and 1MHz gain-bandwidth (green line on the graph). However, for this case, I can't work out how to plot the open-loop gain while the feedback is activated (i.e. right-hand circuit). The blue line on the graph is output voltage divided by v.be(Q3), but this doesn't give the open-loop gain.

So, any hints on how to plot the open-loop gain for this case? Or what the differential/error voltage is defined as for the single-transistor case?
Attached Images
 diffpair_circuit.gif (23.4 KB, 56 views) diffpair_graph.gif (11.3 KB, 53 views) singleQ_circuit.gif (26.7 KB, 51 views) singleQ_graph.gif (12.4 KB, 50 views)

 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 Off Forum Rules
 Forum Jump User Control Panel Private Messages Subscriptions Who's Online Search Forums Forums Home Site     Site Announcements     Forum Problems Amplifiers     Solid State     Pass Labs     Tubes / Valves     Chip Amps     Class D     Power Supplies     Headphone Systems Source & Line     Analogue Source     Analog Line Level     Digital Source     Digital Line Level     PC Based Loudspeakers     Multi-Way     Full Range     Subwoofers     Planars & Exotics Live Sound     PA Systems     Instruments and Amps Design & Build     Parts     Equipment & Tools     Construction Tips     Software Tools General Interest     Car Audio     diyAudio.com Articles     Music     Everything Else Member Areas     Introductions     The Lounge     Clubs & Events     In Memoriam The Moving Image Commercial Sector     Swap Meet     Group Buys     The diyAudio Store     Vendor Forums         Vendor's Bazaar         Sonic Craft         Apex Jr         Audio Sector         Acoustic Fun         Chipamp         DIY HiFi Supply         Elekit         Elektor         Mains Cables R Us         Parts Connexion         Planet 10 hifi         Quanghao Audio Design         Siliconray Online Electronics Store         Tubelab     Manufacturers         AKSA         Audio Poutine         Musicaltech         Aussie Amplifiers         CSS         exaDevices         Feastrex         GedLee         Head 'n' HiFi - Walter         Heatsink USA         miniDSP         SITO Audio         Twin Audio         Twisted Pear         Wild Burro Audio

 Similar Threads Thread Thread Starter Forum Replies Last Post neazoi Solid State 44 29th October 2011 03:47 PM rcollege Solid State 11 15th December 2010 12:18 AM okapi Pass Labs 3 25th December 2009 01:23 PM Leolabs Solid State 28 17th May 2006 09:00 PM Bricolo Solid State 32 20th October 2004 05:25 AM

 New To Site? Need Help?

All times are GMT. The time now is 08:51 PM.