Operational Amplifier Unit 5 PDF

Fundamentals of filters and operational amplifier : filter examples- band-pass filter, low-pass filter, high-pass filter, simple op amp circuits – virtual ground concept, inverting and non-inverting op-amp, properties of operational amplifier, op-amp as an adder and subtrac...

Fundamentals of filters and operational amplifier : filter examples- band-pass filter, low-pass filter, high-pass filter, simple op amp circuits – virtual ground concept, inverting and non-inverting op-amp, properties of operational amplifier, op-amp as an adder and subtractor, op-amp RC circuits –op-amp integrator, op-amp differentiator, op-amp as a comparator and its application in anti-lock braking systems Op-Amp An operational amplifier is an integrated circuit that can amplify weak electric signals. An operational amplifier has two input pins and one output pin. Its basic role is to amplify and output the voltage difference between the two input pins. Operational Amplifiers, also known as Op-amps, are basically a voltage amplifying device designed to be used with components like capacitors and resistors, between its in/out terminals. A is the open loop gain of Op-Amp V1 A V2 =A(V1-V2)  No phase difference Phase difference of 180  Op-Amp is very high gain amplifier, and value of gain is 105-106 Theoretically, if Vd=1 mV, A=105 then Vout= 100 V. Theoretically, if Vd=1 V, A=105 then Vout= 100000 V. Practically, Vout does not exceed the value of biasing voltages. VTC-Voltage Transfer Curve The voltage transfer curve of an operational amplifier (op-amp) is a graphical representation of the relationship between the input voltage and the output voltage of the op-amp. This curve is also known as the input-output characteristic or transfer function of the op-amp.  Here the slope represents the gain of the amplifier, used to be in the range of 10^5 to the 10^6. Now, here let’s say if the gain of the op-amps 10^6. And we are applying 1 microvolt of a signal. Then at the output, we should get 1V of signal. Likewise, let’s say if we apply 10 microvolts of a signal, then at the output, we will get 10 V of output. This particular characteristic of the op-amp is particularly useful when we use this op-amp as a comparator. But if you see this op-amp, this op-amp can also be used in some any other applications. Like, in designing the Active filters Oscillators Waveform converters Analog to digital converters Digital to analog converters. Characteristics of Ideal Operational Amplifiers The ideal op-amp should have this input impedance Ri that is equal to infinity. The output impedance of this op-amp should be equal to zero. The bandwidth of the ideal op-amp, the bandwidth of the ideal op-amp should also be equal to infinity. It means it should support all the frequencies starting from the zero Hertz to the infinite. The gain of the ideal op-amp should also be equal to infinite. Apart from that whenever these two input terminals are zero, that means the input to this op-amps zero, at that time the output of this ideal op-amp should be equal to zero  Slew Rate-The slew rate of an op-amp is a capacity of how rapidly an op-amp can react to a change within the input level. The slew rate formula is (S) = ΔVout/Δt. The slew rate units are V/μs. Common Mode Rejection Ratio If we are applying the same input voltage to this V1 and V2 then the difference between these two voltages will be equal to zero and at the output, we should get zero volts. Likewise, when we are applying different input voltages V1 and V2 to this op-amp then at the output the difference between these two voltages will be get amplified by certain amplifier gain. So, this basically defines how well the op-amp is able to reject the common input voltages that are being applied to both its input terminals and how well it is able to amplify the difference between the two voltages. And it is generally defined as the ratio of differential gain divide by the common mode gain. The ideal op-amp, the value of this common mode rejection ratio should be equal to infinity. OPAMP parameters Sources of Common mode input. 50 Hz-60 Hz noise When circuit is operated in high EM field. The EMI gets coupled to the circuit. Input Offset Current The input offset current, 𝐼𝑂𝑆, is the difference of the input bias currents, expressed as an absolute value. Input Bias Current The input bias current is the average of the two input currents of the op-amp. It is calculated as follows:  Virtual Ground – Opamp Gain = Vo/Vin, As gain is infinite, Vin = 0 Vin = V2 – V1 In the above circuit V1 is connected to ground, so V1 = 0. Thus V2 also will be at ground potential. V2 = 0 Gain=-Rf/R1 Non-inverting amplifier Vin = Vx = R1 x Vo / (R1 + Rf) Vo = ( 1 + Rf/ R1) x Vin Applications of Op-AMP Summing amplifiers The Summing Amplifier is another type of operational amplifier circuit configuration that is used to combine the voltages present on two or more inputs into a single output voltage. Operational amplifier circuit that will amplify each individual input voltage and produce an output voltage signal that is proportional to the algebraic “SUM” of the three individual input voltages V1, V2 and V3. Audio Mixer Circuit Digital to Analogue Converter The Differential Amplifier The differential amplifier amplifies the voltage difference present on its inverting and non-inverting inputs. V+ The Differentiator Amplifier The basic operational amplifier differentiator circuit produces an output signal which is the first derivative of the input signal. The Integrator Amplifier The integrator Op-amp produces an output voltage that is both proportional to the amplitude and duration of the input signal  - + Manufactured by Fairchild Semiconductors IC Circuit  Filters A filter is a circuit capable of passing (or amplifying) certain frequencies while attenuating other frequencies. Thus, a filter can extract important frequencies from signals that also contain undesirable or irrelevant frequencies. Filters can be placed in one of two categories: passive or active. Passive filters include only passive components— resistors, capacitors, and inductors (RC, RL, RLC). In contrast, active filters use active components, such as op-amps, in addition to resistors and capacitors, but not inductors.  Types of Filters Depending upon the frequency of operation, filters can be classified as: 1. Low Pass Filter : The low pass filter only allows low frequency signals from 0 Hz to its cut-off frequency, ƒc point to pass while blocking any higher frequency signals. 2. High Pass Filter : The high pass filter only allows high frequency signals from its cut-off frequency, ƒc point and higher to infinity to pass through while blocking those any lower. 3. Band Pass Filter : The band pass filter allows signals falling within a certain frequency band set up between two points to pass through while blocking both the lower and higher frequencies either side of this frequency band. 4. Band Stop Filter : The band stop filter blocks signals falling within a certain frequency band set up between two points while allowing both the lower and higher frequencies either side of this frequency band.  Types of Filters Low Pass Filter High Pass Filter Band Pass Filter Band Stop Filter  Low Pass Filter The cutoff frequency of an RC low-pass filter is actually the frequency at which the amplitude of the input signal is reduced by 3 dB.  High Pass Filter Band Pass Filter  A band-pass filter works to screen out frequencies that are too low or too high, giving easy passage only to frequencies within a certain range.  Band-pass filters can be made by stacking a low-pass filter on the end of a high-pass filter, or vice versa.  QUICK QUIZ (POLL) Given the lower and higher cut-off frequency of a band- pass filter are 2.5kHz and 10kHz. Determine its bandwidth. a) 750 Hz b) 7500 Hz c) 75000 Hz d) None of the mentioned  Band Stop Filter  A band-stop filter works to screen out frequencies that are within a certain range, giving easy passage only to frequencies outside of that range. Also known as band- elimination, band-reject, or notch filters.  Band-stop filters can be made by placing a low-pass filter in parallel with a high-pass filter. Commonly, both the low-pass and high-pass filter sections are of the “T” configuration, giving the name “Twin-T” to the band-stop combination.  Limitations of Passive Filters 1. The amplitude of the output signal is less than that of the input signal, i.e., the gain is never greater than unity. 2. The load impedance affects the filters characteristics.  With passive filter circuits containing multiple stages, this loss in signal amplitude called “Attenuation” can become quiet severe. One way of restoring or controlling this loss of signal is by using amplification through the use of Active Filters.  As their name implies, Active Filters contain active components such as operational amplifiers, transistors or FETs within their circuit design. They draw their power from an external power source and use it to boost or amplify the output signal. Block Diagram of DC power supply Block Diagram of DC power supply Step Down Transformer and rectifier: The AC supply voltage is usually stepped-down by a transformer and its secondary voltage is converted to a pulsating dc by a diode rectifier. The filter circuit smooth's out the pulsating dc. It blocks almost all of the ac component and almost all of the dc component is passed on to the load resistor. Figure shows the filtered output for a rectified full-wave dc. The only deviation from a perfect dc voltage is the small ac load voltage called ripple. Voltage regulator will provide a constant voltage. 1. Determine the wavelength of light emitted from LED which is made up of GaAsP semiconductor whose forbidden energy gap is 1.875 eV. Mention the colour of the light emitted (Take h = 6.6 × 10-34 Js). 2. In a transistor connected in the common base configuration, α=0.95, IE =1 mA. Calculate the values of IC and IB. 3.