09-10-2012, 02:45 PM
INVERTING MODE OF OPERTIONAL AMPLIFIERS.
INVERTING MODE.doc (Size: 207.5 KB / Downloads: 31)
INTRODUCTION
An operational amplifier, which is often called an op-amp, is a DC-coupled high-gain electronic voltage amplifier with differential inputs and, usually, a single output. Op-amp's very large gain is controlled by negative feedback, which largely determines the magnitude of its output ("closed-loop") voltage gain in amplifier applications.High input impedance at the input terminals (ideally infinite) and low output impedance (ideally zero) are important typical characteristics.
Op-amps are among the most widely used electronic devices today, being used in consumer, industrial, and scientific devices. Op-amps sometimes come in the form of macroscopic components, or as integrated circuit 'cells' or patterns that can be reprinted several times on one chip that is more complex, such as for a cell phone.
INVERTING MODE OF OP-AMP-
Above given example is a typical amplifier in inverting mode,because the voltage source is placed in the inverting input terminal . In such a –ve feedback amplifier circuit the non –inverting terminal should be grounded via the same value resistance R1 to guarantee the balance between two points.
In many cases the open – loop gain (G)op of an op-amp may not be infinetly high so that the input terminal may have a very small but non-zero voltage.
USAGE-
Op-amps are among the most widely used electronic devices today, being used in a vast array of consumer, industrial, and scientific devices.
Modern designs are electronically more rugged than earlier implementations and some can sustain direct short circuits on their outputs without damage.
The op-amp is one type of differential amplifier. Other types of differential amplifier include the fully differential amplifier (similar to the op-amp, but with two outputs), the instrumentation amplifier (usually built from three op-amps), the isolation amplifier (similar to the instrumentation amplifier, but which works fine with common-mode voltages that would destroy an ordinary op-amp), and negative feedback amplifier (usually built from one or more op-amps and a resistive feedback network).
The basic function of the Op-Amp is to multiply a voltage level by the gain of the amplifier. If we were to couple a DC level of +1v into the + input of our Op-Amp then the output would be 1v X 1000000 or one Million volts. The output, however, cannot exceed the supply voltage, so the output will be +20v DC.
Applications-
Use in electronics system design-
The use of op-amps as circuit blocks is much easier and clearer than specifying all their individual circuit elements (transistors, resistors, etc.), whether the amplifiers used are integrated or discrete. In the first approximation op-amps can be used as if they were ideal differential gain blocks; at a later stage limits can be placed on the acceptable range of parameters for each op-amp.
Circuit design follows the same lines for all electronic circuits. A specification is drawn up governing what the circuit is required to do, with allowable limits. For example, the gain may be required to be 100 times, with a tolerance of 5% but drift of less than 1% in a specified temperature range; the input impedance not less than one megohm; etc.
A basic circuit is designed, often with the help of circuit modeling (on a computer). Specific commercially available op-amps and other components are then chosen that meet the design criteria within the specified tolerances at acceptable cost. If not all criteria can be met, the specification may need to be modified.
CONCLUSION
1. This definition hews to the convention of measuring op-amp parameters with respect to the zero voltage point in the circuit, which is usually half the total voltage between the amplifier's positive and negative power rails.
2. That the output cannot reach the power supply voltages is usually the result of limitations of the amplifier's output stage transistors.
3. The output of older op-amps can reach to within one or two volts of the supply rails. The output of newer so-called "rail to rail" op-amps can reach to within millivolts of the supply rails when providing low output currents.