{"id":37187,"date":"2020-10-09T09:03:18","date_gmt":"2020-10-09T01:03:18","guid":{"rendered":"\/blog\/?p=37187"},"modified":"2020-10-30T15:27:26","modified_gmt":"2020-10-30T07:27:26","slug":"operational-amplifier-basic-knowledge-circuit-and-application","status":"publish","type":"post","link":"https:\/\/www.seeedstudio.com\/blog\/2020\/10\/09\/operational-amplifier-basic-knowledge-circuit-and-application\/","title":{"rendered":"Basic Knowledge, Circuit and Application of Operational Amplifier(op amp)"},"content":{"rendered":"\n

What is an op amp?<\/strong><\/p>\n\n\n\n

Operational amplifiers (referred to as op amps) are high-gain voltage amplifiers with DC coupling<\/a>, differential mode<\/a> input and usually single-ended output, because they were mainly used in addition, multiplication and other operational circuits at the beginning. An ideal operational amplifier must have the following characteristics: infinite input impedance<\/a>, equal to zero output impedance<\/a>, infinite open loop gain<\/a>, infinite common mode rejection ratio(CMRR)<\/a> , infinite bandwidth<\/a>. The most basic operational amplifier is shown below. Operational amplifier modules generally include positive input (OP_P), negative input (OP_N) and output (OP_O).<\/p>\n\n\n\n

\"\"
The most basic op amp <\/figcaption><\/figure><\/div>\n\n\n\n

Two basic concepts of op amp <\/strong><\/p>\n\n\n\n

“Virtual short” and “virtual\nbroken” are two basic concepts of operational amplifiers. When analyzing\nlinear application circuits of operational amplifiers, the analysis process of\napplication circuits can be simplified. Operational circuits formed by\noperational amplifiers require a certain functional relationship between input\nand output, so both conclusions can be applied.<\/p>\n\n\n\n

\u201cvirtual short\u201d <\/strong><\/p>\n\n\n\n

The voltage amplification of the\noperational amplifier is very large. Usually, the open-loop voltage\namplification of the general-purpose operational amplifier is above 80dB, and\nthe output voltage of the op amp is limited, generally between 10 V and 14 V. Therefore,\nthe differential mode input voltage of the op amp is less than 1mV, and the\npotential of the two input terminals is approximately equal, which is\nequivalent to “short circuit”. The greater the open-loop voltage\nmagnification, the closer the potentials of the two input terminals are to\nequal.<\/p>\n\n\n\n

“Virtual short” means that when\nthe op amp is in a linear state, the two inputs can be considered equal\npotential. This characteristic is called false short circuit, or virtual short\nfor short. Obviously, these two input terminals can\u2019t be truly short-circuited.<\/p>\n\n\n\n

\u201cvirtual broken\u201d<\/strong><\/p>\n\n\n\n

Because of the differential mode input\nresistance of operation amplifier is very big, general-purpose operational\namplifier input resistance is usually more than 1 m \u03a9. Therefore, the current\nflowing into the op amp input is usually less than 1uA and far less than the\ncurrent of the external circuit at the input. Thus, the two inputs to an op amp\nare generally considered open, with the greater the input resistance, the\ncloser the two inputs are from the path. <\/p>\n\n\n\n

“Virtual broken” means that when the analysis op amp is in a linear state, the two inputs can be treated as an equivalent open circuit. This feature is called false open circuit, or virtual break for short. Obviously, these two input terminals can\u2019t really be disconnected.<\/p>\n\n\n\n

Two basic circuits of op amp<\/strong><\/p>\n\n\n\n

Negative feedback circuit<\/strong><\/p>\n\n\n\n

\"\"
Negative feedback circuit of op amp<\/figcaption><\/figure><\/div>\n\n\n\n

The polarity of the feedback signal and the input signal are opposite\nor the direction of change is opposite (inverted), the result of superposition\nwill weaken the net input signal. This kind of feedback is called a negative\nfeedback amplifier circuit. The sampling of negative feedback generally uses\ncurrent sampling or voltage sampling. The use of negative feedback makes the\nclosed-loop gain of the amplifier stabilized, eliminating the influence of the\nopen-loop gain. Negative feedback also affects the amplifier’s input and output\nimpedance. Voltage mixing increases the input impedance, current mixing\ndecreases the input impedance; current sampling increases the output impedance,\nand voltage sampling decreases the output impedance. The use of negative feedback\ncan also greatly reduce the distortion generated by the amplifier in a steady\nstate, and can reduce various interference levels within the amplifier. <\/p>\n\n\n\n

Positive feedback circuit<\/strong><\/p>\n\n\n\n

\"\"
Positive feedback circuit of op amp <\/figcaption><\/figure><\/div>\n\n\n\n

The polarity of the feedback signal is the same as the polarity of the\ninput signal of the system, thereby enhancing the net input signal of the\nsystem, which is called positive feedback mode. In the electronic amplifier\ncircuit, the use of positive feedback can increase the amplifier gain and\nincrease the amplifier’s frequency selectivity to generate useful periodic\noscillation signals.<\/p>\n\n\n\n

Operational amplifier application<\/strong><\/p>\n\n\n\n

Generally, using negative feedback can ensure the stable operation of the circuit. And the use of positive feedback can be applied to systems with oscillating signals. The operational amplifier has the functions of addition, subtraction, proportional amplification, integral differentiation, etc. There are many operational amplifier circuits that cover most of the main analog functions required.\u00a0Therefore, operational amplifiers have become the workhorse for analog electronics designers, which have a wide range of uses in the electronics industry, especially general purpose op amps<\/a>. They can be used as precision AC and DC<\/a> amplifiers, active filters<\/a>, oscillators<\/a> and voltage comparators<\/a> when connected to appropriate feedback networks.<\/p>\n\n\n\n

Should you need to realize your circuit design as a physical printed circuit board, Seeed Fusion can take care of PCB manufacturing and assembly. Trusted by millions of electronics engineers, hobbyists and makers around the world, Seeed promises mature PCB manufacturing and fabrication with low costs, quick build time and 100% quality guaranteed. Get an instant online quotation at Seeed Fusion<\/a> now. <\/p>\n","protected":false},"excerpt":{"rendered":"

What is an op amp? Operational amplifiers (referred to as op amps) are high-gain voltage<\/p>\n","protected":false},"author":3528,"featured_media":37188,"comment_status":"open","ping_status":"closed","sticky":false,"template":"","format":"standard","meta":{"_lmt_disableupdate":"","_lmt_disable":"","_price":"","_stock":"","_tribe_ticket_header":"","_tribe_default_ticket_provider":"","_tribe_ticket_capacity":"0","_ticket_start_date":"","_ticket_end_date":"","_tribe_ticket_show_description":"","_tribe_ticket_show_not_going":false,"_tribe_ticket_use_global_stock":"","_tribe_ticket_global_stock_level":"","_global_stock_mode":"","_global_stock_cap":"","_tribe_rsvp_for_event":"","_tribe_ticket_going_count":"","_tribe_ticket_not_going_count":"","_tribe_tickets_list":"[]","_tribe_ticket_has_attendee_info_fields":false,"iawp_total_views":0,"footnotes":""},"categories":[1],"tags":[3138],"class_list":["post-37187","post","type-post","status-publish","format-standard","has-post-thumbnail","hentry","category-news","tag-circuit"],"yoast_head":"\nBasic Knowledge, Circuit and 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