Negative feedback amplifier |
| 1. Positive feedback and negative feedback |
| Sending some quantity from the output of the amplifier back to the input is called feedback. If the phase of the feedback is the same as the input, and the increase in the amplification factor after the feedback is added is called positive feedback; if the phase of the feedback is opposite to the input, the feedback is used to oscillate the circuit, and the negative feedback is used to improve the performance of the amplifier . |
| 2. Feedback method and feedback effect |
| The feedback effect is closely related to the nature and method of the feedback quantity. If the negative feedback quantity is proportional to the output voltage, the feedback effect can stabilize the output voltage and the output resistance is reduced, which is called voltage negative feedback; if the negative feedback quantity is related to the output The current is proportional to its feedback effect, which can stabilize the output current and increase the output resistance, which is called current feedback. According to the access form of the feedback at the input, it is divided into series feedback and parallel feedback. The feedback quantity of series feedback is connected in series to the input loop in series, and the feedback quantity of parallel feedback is connected in parallel to the input loop in parallel. The negative feedback in series can increase the input resistance, while the negative feedback in parallel reduces the input resistance. |
| Third, the judgment method of feedback |
| The positive or negative feedback is judged by the instantaneous polarity method. First, assume that the input signal has a certain instantaneous polarity, and then push out the instantaneous polarity of each input and output step by step according to the principle of the input and output of the single-stage common-emitter amplifier. The polarity of the feedback quantity fed back to the input terminal is the assumed polarity of the original input signal: if both polarities are the same, it is positive feedback, and if the polarities are opposite, it is negative feedback. Whether the voltage feedback or the current feedback is determined by the imaginary output AC short-circuit method. After short-circuiting the effective current at the output, if the feedback value disappears, it is voltage feedback, if there is still a feedback amount, it is current feedback, Whether the series feedback or the parallel feedback examines the connection mode of the input loop to judge. If the feedback amount and the input signal are added by voltage, it is series feedback, and if it is added by current, it is parallel feedback. The four forms of negative feedback circuits are listed in Table 1, and their related calculation formulas are listed in Table 2. |
Table 1. Three forms of feedback |
|
Table 2. Parameter calculation of four forms of negative feedback |
| ||||||||||||||||
Follow WeChat
Interesting and informative information and technical dry goods
Download Audiophile APP
Create your own personal electronic circle
Follow the audiophile class
Lock the latest course activities and technical live broadcast
comment
Publish
related suggestion
Quit '; * / var login_content =' write an article ![]()
'+ data.username +'
Set exit '; $ (' # login_area '). Html (login_content); var win_width = $ (window) .width (); if (win_width> 1000) {$ ("# mine"). MouseDelay (200) .hover (function () {$ ("# mymenu"). show ();}, function () {$ ("# mymenu"). hide ();});}} else {var content = 'Login Registration'; $ ('# login_area'). html (content); $ (". special-login"). click (function (e) {$ .tActivityLogin (); return false;});}});} $ (function () {// comment ------------------------------- var comment = $ ("# comment"); var comment_input = $ ("# comContent"); // Submit comment click event interaction $ ("# comSubmit2"). on ('click', function () {var content = comment_input.text (); // Empty input box comment_input. html (""). focus (); // Submit data to the server $ .ajax ({url: '/plus/arcComment.php', data: {aid: $ ("# webID"). val (), dopost : 'apiPubComment', content: content}, type: 'post', dataType: 'json', success: function (data) {// Data format returned: if (data.status == "successed") {// Build temporary comment DOM var dom = ''; dom + = '
'; dom + =' ![]()
'; dom + ='
'; dom + ='
'+ data.data.username +' '; dom + ='
'; dom + =' '+ content +' '; dom + =' '; dom + =' just now '; dom + =' '; dom + =' '; // insert a temporary comment to the list $ ("# comment ") .append (dom);} if (data.status ==" failed ") {// alert (data.msg); layer.msg (data.msg);}}}); return false;}); (function () {/ * * Insert single sign-on JS * / var setHost = 'https://passport.elecfans.com'; // Set domain name var script = document.createElement ('script'); script.type = 'text / javascript'; script.src = setHost + '/public/pc/js/t.passport.js'; script.setAttribute ("id", "sso_script"); script.setAttribute ("data-ssoSite", setHost); script.setAttribute ("data-ssoReferer", encodeURIComponent (location.href)); script.setAttribute ("data-ssoSiteid", "11"); var body = document.getElementsByTagName ("body"). item ( 0); body.appendChild (script);}) () / * * It is recommended to modify the style of the article without a picture * * / $ (". Article .thumb"). Each (function () {if ($ (this). find ('img'). attr ('src') == "") {$ (this) .find ('img'). remove (); $ (this) .parent (). css ('padding-left ',' 0px ');}}); / * Baidu share * / window._bd_share_config = {common: {bdText: '', // Custom share content bdDesc: '', // Custom share summary bdUrl: window.location.href, // Custom share URL address bdPic: ''} , share: [{"bdSize": 60, "bdCustomStyle": true}]} with (document) 0 [(getElementsByTagName ('head') [0] || body) .appendChild (createElement ('script')). src = 'http://bdimg.share.baidu.com/static/api/js/share.js?cdnversion=' + ~ (-new Date () / 36e5)]; var add_url = '/ d / article / write / '; // var check_allow = "{: U (' Api / iscantalk ')}"; var check_allow = "/ d / api / iscantalk"; var click_items_length = $ ('. art_click_count '). length; if ( click_items_length> 0) {var id_str = ''; $ ('. art_click_count'). each (function () {id_str + = $ (this) .attr ('data-id') + ',';}) // var url = "{: U ('Api / getclickbyids')}"; var url = "/ d / api / getclickbyids"; var id_data = 'id_str =' + id_str; $ .ajax ({url: url, data: id_data, type: 'post', dataType: 'json', success: function (re) {if (re.list.length> = 1) {var list = re.list; for (var i in list) {var t emp_id = list [i] ['id']; var temp_span = $ (". art_click_count [data-id =" + temp_id + "]") temp_span.html (list [i] ['click']);}} }})} $ ("# comContent"). click (function () {if (now_uid == '') {$ .tActivityLogin (); return false;}}) $ (function () {var follow_wrap = $ ( ".author-collect"); var now_uid = "{$ _super ['uid']}"; var face_src = "{$ _super ['uface']}"; var getFollowNum = $ (". followNum strong"). html (); // Follow $ (window) .on ('click', '.author-collect', function () {if (now_uid == '') {$ .tActivityLogin (); return false;} if ( $ (this) .attr ('id') == 'follow') {$ .post ('/ d / user / follow', {tuid: article_user_id}, function (data) {// Data format returned: if (data.status == "successed") {$ (". followNum strong"). html (++ getFollowNum); follow_wrap.html ('followed'). attr ('id', 'cancelFollow'). css ( 'background', '# 999'); var follow_user = ' ![]()
'; $ (' # follow_list '). append (follow_user);} if (data.status == "failed") {alert (data.msg);}});} else {// Unfollow if ($ ( this) .attr ('id') == 'cancelFollow') {$ .post ('/ d / user / cancelFollow', {tuid: article_user_id}, function (data) {// Data format returned: if (data .status == "successed") {follow_wrap.html ('Follow'). attr ('id', 'follow'). css ('background', '# f90'); $ (". followNum strong"). html (-getFollowNum); $ ('# follow_list .face'). each (function () {var target_uid = $ (this) .attr ('data-uid'); if (target_uid == now_uid) {$ ( this) .remove ();}})} if (data.status == "failed") {alert (data.msg);}}); return false;}}});});}); / * var myface = "{$ _super ['uid'] | avatar}"; var myname = "{$ _super ['username']}"; var article_id = {$ article ['id']}; var article_user_id = {$ article ['mid']}; // Article author ID $ (function () {<notempty name = "clearnum"> // Reduce the number of reminders var count = parseInt ($ ("# noticeCount"). html ()); count = count-{$ clearnum}; $ ("# noticeCount"). html (count); if ( count
LED street lamp refers to the street lamp made with LED light source, which has the unique advantages of high efficiency, safety, energy saving, environmental protection, long life, fast response speed, high color rendering index, and is of great significance to urban lighting energy saving.
Led Road Light,Led Off Road Lights,Led Roadway Lighting,Cob Led Road Light
Yangzhou Heli Photoelectric Co., Ltd. , https://www.heli-eee.com