igure 5.1 A pplying the voltage divider rule, the voltage at the base of Q3 is Publish Log In Sign Up

Transcription

1 Publish Log In Sign Up Search books, presentatio Search Explore Documents Books - FictionBooks - Non-fictionHealth & MedicineBrochures/CatalogsGovernment DocsHow-To Guides/ManualsMagazines/NewspapersRecipes/MenusSchool Work+ all categories RecentFeatured Download People 0 AuthorsStudentsResearchersPublishersGovernment BackComment & NonprofitsBusinessesMusiciansArtists & DesignersTeachers+ all categories Most FollowedPopular Link Embed Zoom 1 of 38 Readcast Constant Current Tw eet Bias: Share In the dc analysis of differential amplifier, we have seen that the emitter current IE depends upon the value of bdc. To make operating point stable I E current should be constant irrespective value ofbdc. For constant IE, R E should be very large. This also increases the value of CMRR but if R E value is increased to very large value, IE (quiescent operating current) decreases. To maintain same value of IE, the emitter supply V EE must be increased. To get very high value of resistance R E and constant IE, current, current bias is used. Search This Document Search Search History: Searching... Result 00 of results for result for p. igure 5.1 fig1 shows the dual input balanced output differential amplifier using a constant current bias. The resistance R E is replace by constant current transistor Q3. The dc collector current in Q3 is established by R 1, R 2, & R E. A pplying the voltage divider rule, the voltage at the base of Q3 is 1/27

2 Because the two halves of the differential amplifiers are symmetrical, each has half of the current IC3. The collector current, IC3 in transistor Q3 is fixed because no signal is injected into either the emitter or the base of Q3. Besides supplying constant emitter current, the constant current bias also provides a very high source resistance since the ac equivalent or the dc source is ideally an open circuit. Therefore, all the performance equations obtained for differential amplifier using emitter bias are also valid. A s seen in IE expressions, the current depends upon V BE3. If temperature changes, V BE changes and current I E also changes. To improve thermal stability, a diode is placed in series with resistance R 1as shown in f ig2. Fig. 2 This helps to hold the current I E3 constant even though the temperature changes. A pplying KVL to the base circuit of Q3. Therefore, the current IE3 is constant and independent of temperature because of the added diode D. Without D the current would vary with temperature because V BE3 decreases approximately by 2mV/ C. The diode has same temperature dependence and hence the two variations cancel each other and IE3 does not vary appreciably with temperature. Since the cut in voltage 2/27

3 3/27

4 4/27

5 5/27

6 6/27

7 7/27

8 8/27

9 9/27

10 10/27

11 11/27

12 12/27

13 13/27

14 14/27

15 15/27

16 16/27

17 17/27

18 18/27

19 19/27

20 20/27

21 21/27

22 22/27

23 23/27

24 More From This User 38 p. Constant Current Bias KRISHNAVINOD 2212 Reads 440 p. Op Amps for Everyone KRISHNAVINOD 316 Reads 24/27

25 35 p. Operational Amplifier(Phe 10) KRISHNAVINOD 405 Reads next Related 14 p. Lecture-6_opamp_dc_parameters Dhiyagu Sridar 303 Reads 106 p. acd Vivek Gandhi 233 Reads 33 p. Operational Amplifiers Sanka Jeewantha 62 Reads 25/27

26 next Leave a Comment You must be logged in to leave a comment. Submit Characters: 400 You must be logged in to leave a comment. Submit Characters:... Constant Current Bias Download or Print Add To A Collection 2,212 Reads 9 Readcasts 1 Embed Views Published by ethicaltechnologyforso... Follow Info and Rating Category: Uncategorized. Rating: Upload Date: 11/05/2010 Copyright: Tags: Attribution Non-commercial This document has no tags. Free download as PDF File (.pdf), Word Doc (.doc /.docx), text file (.txt) or read online for free. Flag document for inapproriate content Search This Document Search TIP Press Ctrl-F F to quickly search anywhere in the document. More From This User Constant Current Bias KRISHNAVINOD Reads: 2212 Op Amps for Everyone KRISHNAVINOD Reads: 316 Operational Amplifier(Phe 10) KRISHNAVINOD Reads: KRISHNAVINOD Reads: 76 Internship Brochure KRISHNAVINOD Reads: 126 Prev Next Related Lecture-6_opamp_dc_parameters Dhiyagu Sridar Reads: 303 acd Vivek Gandhi Reads: 233 Operational Amplifiers Sanka Jeewantha Reads: 62 Operational Amplifiers muhammad yunus yasin Reads: 197 Operational Amplifiers Basil Mathew 26/27

27 Reads: 201 Prev Next About What is Scribd? Blog Join our team! Advertise with us Support Partners Legal Get started AdChoices Help FAQ Press Publishers Developers / API Terms Privacy Copyright Copyright 2012 Scribd Inc. Language: English 27/27