walid Posted May 6, 2012 Report Share Posted May 6, 2012 Hi,If there are two BJT small signal amplifiers (common Emitter) cascade connected using a suitable decoupling capThe first preamp has an o/p imeadance Zo, and the second has an i/p impedance ZinNow we have Zo and Zin and a cap betwwen themMy question is: Is the connection series or parallel? That, is the o/p voltage divided or the o/p current? Quote Link to comment Share on other sites More sharing options...
Hero999 Posted May 6, 2012 Report Share Posted May 6, 2012 Where's the schematic? Please stop asking questions without one. Quote Link to comment Share on other sites More sharing options...
walid Posted May 6, 2012 Author Report Share Posted May 6, 2012 Hi Hero999At first I like to thank you on the fast of responseI mean here is if the output impedance of the first stage = 10k and the input impedance of the second phase = 10k Are these two impedances connected in series or parallel?thanks alot Quote Link to comment Share on other sites More sharing options...
audioguru Posted May 7, 2012 Report Share Posted May 7, 2012 There is no decoupling capacitor. Instead there are coupling capacitors. C3 couples the transistors together. C5 is the input coupling capacitor and C4 is the output coupling capacitor.Instead of wrongly guessing the impedances, calculate that the output impedance of the first transistor is 4.7k ohms and the input impedance of the 2nd transistor is 2.41k ohms. They are in parallel so the first transistor has a total collector load of 10k//2.41k= 1.94k ohms so its gain is 0.41 times the gain when it has no load. Quote Link to comment Share on other sites More sharing options...
walid Posted May 7, 2012 Author Report Share Posted May 7, 2012 Thanks audioguru I am very happy with your presence and I hope to be in good health and happy in your life.I have read in a book "The art of electroncs" page 66, the followingI take it most likely the first stage is a source of signal with internal resistance (Zout1), and the second stage with input resistance of (Zin2),,,, what would you say?Note: I miss you here too long and I had to register on many forums and I put the same question to ensure the receipt of a convincing answer from one of them. Quote Link to comment Share on other sites More sharing options...
Kevin Weddle Posted May 18, 2012 Report Share Posted May 18, 2012 It's more of a dc electronics circuit. The leveling frequency changes the properties of circuit interconnection and impedance. Quote Link to comment Share on other sites More sharing options...
Guest remonx6 Posted August 2, 2013 Report Share Posted August 2, 2013 Impedance relation between 2 Bjts use this formula regarding this issueZout and Zin form a voltage divider. The actual input voltage seen by the second amplifer is is calcluated from that, i.e. V = Vin * Zin / (Zin + Zout) Quote Link to comment Share on other sites More sharing options...
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