Submitted By:
MANISH SHARMA

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OPAMP APPLICATION, INTERFACING LCD & ADC7829 WITH 8051 MICROCONTROLLER at LASTEC, DRDO
vision, Mission & Values of LASTEC
VISION:
Be the Centre of Excellence in the field of Lasers and Opto-Electronics.
MISSION:
Develop and deliver directed energy weapon systems for the services. Carry out advanced research in the field of Lasers, Photonics and Opto-Electronics.
The Laser Science And Technology Centre had its beginning in 1950 as the Defence Science Laboratory (DSL)) established as a nucleus laboratory of DRDO (then known as Defence Science Organisation). In the beginning, DSL operated from the National Physical Laboratory building.Later, on April 9th 1960, it was shifted to Metcalfe House and Menon inaugurated by then Raksha Mantri Dr Krishna in the presence of Pt. Jawahar Lal Nehru. DSL had seeded for as many as 15 present DRDO labs with core groups working in many diverse area. In 1982, the Laboratory moved to a new technical building in Metcalfe House complex and was rechristened as Defence Science Centre.
AREAS OF WORK
Operational amplifier
An operational amplifier, which is often called an op-amp, is a high-gain electronic voltage amplifier with a differential input and, usually, a single-ended output.[1] An op-amp produces an output voltage that is typically millions of times larger than the voltage difference between its input terminals.
Typically the 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, or the transfer function required (in analog computers). Without negative feedback, and perhaps with positive feedback for regeneration, an op-amp essentially acts as a comparator. High input impedance at the input terminals (ideally infinite) and low output impedance at the output terminal(s) (ideally zero) are important typical characteristics.
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 with tolerance to 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).
Circuit notation
The circuit symbol for an op-amp is shown above:
• : non-inverting input
• : inverting input
• : output
• : positive power supply
• : negative power supply
Ideal and real op-amps
An equivalent circuit of an operational amplifier that models some resistive non-ideal parameters.
An ideal op-amp is usually considered to have the following properties, and they are considered to hold for all input voltages:
• Infinite open-loop gain (when doing theoretical analysis, a limit may be taken as open loop gain AOL goes to infinity)
• Infinite bandwidth (i.e., the frequency magnitude response is considered to be flat everywhere with zero phase shift).
• Infinite input impedance (so, in the diagram, , and zero current flows from to )
• Zero input current (i.e., there is assumed to be no leakage or bias current into the device)
• Zero input offset voltage (i.e., when the input terminals are shorted so that , the output is a virtual ground or vout = 0).
• Infinite slew rate (i.e., the rate of change of the output voltage is unbounded) and power bandwidth (full output voltage and current available at all frequencies).
• Zero output impedance (i.e., Rout = 0, so that output voltage does not vary with output current)
• Infinite Common-mode rejection ratio (CMRR)
In practice, none of these ideals can be realized, and various shortcomings and compromises have to be accepted. Depending on the parameters of interest, a real op-amp may be modeled to take account of some of the non-infinite or non-zero parameters using equivalent resistors and capacitors in the op-amp model. The designer can then include the effects of these undesirable, but real, effects into the overall performance of the final circuit. Some parameters may turn out to have negligible effect on the final design while others represent actual limitations of the final performance, that must be evaluated.
Real operational amplifiers suffer from several non-ideal effects:
Finite gain
Open-loop gain is infinite in the ideal operational amplifier but finite in real operational amplifiers. Typical devices exhibit open-loop DC gain ranging from 100,000 to over 1 million. So long as the loop gain (i.e., the product of open-loop and feedback gains) is very large, the circuit gain will be determined entirely by the amount of negative feedback (i.e., it will be independent of open-loop gain). In cases where closed-loop gain must be very high, the feedback gain will be very low, and the low feedback gain causes low loop gain; in these cases, the operational amplifier will cease to behave ideally.
Finite input impedances
The differential input impedance of the operational amplifier is defined as the impedance between its two inputs; the common-mode input impedance is the impedance from each input to ground. MOSFET-input operational amplifiers often have protection circuits that effectively short circuit any input differences greater than a small threshold, so the input impedance can appear to be very low in some tests. However, as long as these operational amplifiers are used in a typical high-gain negative feedback application, these protection circuits will be inactive. The input bias and leakage currents described below are a more important design parameter for typical operational amplifier applications.
Non-zero output impedance
Low output impedance is important for low-impedance loads; for these loads, the voltage drop across the output impedance of the amplifier will be significant. Hence, the output impedance of the amplifier limits the maximum power that can be provided. In a negative-feedback configuration, the output impedance of the amplifier is effectively lowered; thus, in linear applications, op-amps usually exhibit a very low output impedance indeed. Negative feedback can not, however, reduce the limitations that Rload in conjunction with Rout place on the maximum and minimum possible output voltages; it can only reduce output errors within that range.
Input current
Due to biasing requirements or leakage, a small amount of current flows into the inputs. When large resistors or sources with high output impedances are used in the circuit, these small currents can produce large unmodeled voltage drops. If the input currents are matched, and the impedance looking out of both inputs are matched, then the voltages produced at each input will be equal. Because the operational amplifier operates on the difference between its inputs, these matched voltages will have no effect (unless the operational amplifier has poor CMRR, which is described below). It is more common for the input currents (or the impedances looking out of each input) to be slightly mismatched, and so a small offset voltage can be produced. This offset voltage can create offsets or drifting in the operational amplifier. It can often be nulled externally; however, many operational amplifiers include offset null or balance pins and some procedure for using them to remove this offset. Some operational amplifiers attempt to nullify this offset automatically.
Input offset voltage
This voltage, which is what is required across the op-amp's input terminals to drive the output voltage to zero, is related to the mismatches in input bias current. In the perfect amplifier, there would be no input offset voltage. However, it exists in actual op-amps because of imperfections in the differential amplifier that constitutes the input stage of the vast majority of these devices. Input offset voltage creates two problems: First, due to the amplifier's high voltage gain, it virtually assures that the amplifier output will go into saturation if it is operated without negative feedback, even when the input terminals are wired together. Second, in a closed loop, negative feedback configuration, the input offset voltage is amplified along with the signal and this may pose a problem if high precision DC amplification is required or if the input signal is very small.
Common mode gain
A perfect operational amplifier amplifies only the voltage difference between its two inputs, completely rejecting all voltages that are common to both. However, the differential input stage of an operational amplifier is never perfect, leading to the amplification of these identical voltages to some degree. The standard measure of this defect is called the common-mode rejection ratio (denoted CMRR). Minimization of common mode gain is usually important in non-inverting amplifiers (described below) that operate at high amplification