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A-GROUP 130330109036- Gansham Malavya 130330109037- Prashant Malavya 130330109038- Rajat Mandal 130330109039-Dhiren Manga 130330109040- Alhas Manya Guided by- Prof. Reema Operational Amplifier Instrumentation Amplifier Differential input & differential output amplifier V to I and I to V convertor Integrator Differentiator Comparator Non-Linear Amplifier Phase Shift Oscillator Instrumentation Amplifier Defination:An instrumentation (or instrumentational) amp lifieris a type of differential amplifier that has been outfitted with input buffer amplifiers, which eliminate the need for input impedance matching and thus make the amplifier particularly suitable for use in measurement and test equipment. Additional characteristics include very lowDC offset, low drift, low noise, very high open-loop gain, very high common-mode rejection ratio, and very highinput impedances. Instrumentation amplifiers are used where great accuracy and stability of the circuit both short and long-term are required. Instrumentation Amplifier vo 1 v1 I I v1 v2 R1 I v2 vo 2 Although the instrumentation amplifier is usually shown schematically identical to a standard operational amplifier (op-amp), the electronic instrumentation amp is almost always internally composed of 3 opamps. These are arranged so that there is one op-amp to buffer each input (+,−), and one to produce the desired output with adequate impedance matching for the function.[1][2] The most commonly used instrumentation amplifier circuit is shown in the figure. The gain of the circuit is The rightmost amplifier, along with the resistors labelled and is just the standard differential amplifier circuit, with gain = and differential input resistance = 2· . The two amplifiers on the left are the buffers. With removed (open circuited), they are simple unity gain buffers; the circuit will work in that state, with gain simply equal to and high input impedance because of the buffers. The buffer gain could be increased by putting resistors between the buffer inverting inputs and ground to shunt away some of the negative feedback; however, the single resistor between the two inverting inputs is a much more elegant method: it increases the differential-mode gain of the buffer pair while leaving the common-mode gain equal to 1. This increases the common-mode rejection ratio (CMRR) of the circuit and also enables the buffers to handle much larger common-mode signals without clipping than would be the case if they were separate and had the same gain. Another benefit of the method is that it boosts the gain using a single resistor rather than a pair, thus avoiding a resistor-matching problem (although the two s need to be matched), and very conveniently allowing the gain of the circuit to be changed by changing the value of a single resistor. A set of switch-selectable resistors or even a potentiometer can be used for , providing easy changes to the gain of the circuit, without the complexity of having to switch matched pairs of resistors. The ideal common-mode gain of an instrumentation amplifier is zero. In the circuit shown, common-mode gain is caused by mismatches in the values of the equally numbered resistors and by the mis-match in common mode gains of the two input op-amps. Obtaining very closely matched resistors is a significant difficulty in fabricating these circuits, as is optimizing the common mode performance of the input op-amps.[3] An instrumentation amp can also be built with two op-amps to save on cost and increase CMRR, but the gain must be higher than two (+6 dB).[4][5] Single-ended output If the differential output is not desired, then only one output can be used (taken from just one of the collectors (or anodes or drains), disregarding the other output without a collector inductor; this configuration is referred to as single-ended output. The gain is half that of the stage with differential output. To avoid sacrificing gain, a differential to single-ended converter can be utilized. This is often implemented as a current mirror Single-ended input The differential pair can be used as an amplifier with a single- ended input if one of the inputs is grounded or fixed to a reference voltage (usually, the other collector is used as a singleended output) This arrangement can be thought as of cascaded common-collector and common-base stages or as a buffered common-base stage. The emitter-coupled amplifier is compensated for temperature drifts, VBE is cancelled, and the Miller effect and transistor saturation are avoided. That is why it is used to form emittercoupled amplifiers (avoiding Miller effect), phase splitter circuits (obtaining two inverse voltages), ECL gates and switches (avoiding transistor saturation), etc. Example #1: Voltage Comparator is = 0 i1 = 0 i2 = 0 Note that the inverting input and non-inverting input terminals have rotated in this schematic. Example #1 (con’t) The internal circuitry in the op amp tries to force the voltage at the inverting input to be equal to the noninverting input. As we will see shortly, a number of op amp circuits have a resistor between the output terminal and the inverting input terminals to allow the output voltage to influence the value of the voltage at the inverting input terminal. Inverting Integrator Now replace resistors R and R by complex a Zf f components Za and Zf, respectively, therefore Zf Vo Vin Za Supposing in (i) The feedback component is a capacitor C, i.e., Z 1 f jC (ii) The input component is a resistor R, Za = R 1 Therefore, the closed-loop gain (Vo/Vin) vo (t ) v ( t ) dt i become: RC Za V ~ in V o V ~ vi (t ) Vi e jt + C R V o + where What happens if Za = 1/jC whereas, Zf = R? Inverting differentiator Ref:080114HKN Operational Amplifier 13 Op-Amp Integrator Example: (a) Determine the rate of change +5V 0 of the output voltage. C R 100s (b) Draw the output waveform. V i 10 k 0.01F V o + Vo(max)=10 V Solution: (a) Rate of change of the output voltage Vo V 5V i t RC (10 k)(0.01 F ) 50 mV/ s +5V 0 V i 0 (b) In 100 s, the voltage decrease Vo (50 mV/ s)(100μs) 5V Ref:080114HKN Operational Amplifier -5V -10V V o 14 Op-Amp Differentiator R C 0 to t1 t2 V i V o 0 + to t1 t2 dV vo i RC dt Ref:080114HKN Operational Amplifier 15