Operational amplifier
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An operational amplifier (op-amp) is an integrated circuit that can amplify or compare signals. It consists of transistors, resistors, and capacitors. Op-amps are used to build amplifiers, summers, integrators, differentiators, and comparators. They obey golden rules to make the difference between their input pins zero. Op-amps are also used in analog to digital converters, which sample analog signals and convert them to digital signals for processing.
Operational amplifier
- 2. What is an Op-Amp Low cost integrating circuit consisting of: • Transistors • Resistors • Capacitors Able to amplify a signal due to an external power supply Name derives from its use to perform operations on a signal.
- 3. Applications of Op-Amps Simple Amplifiers Summers Comparators Integrators Differentiators Analog to Digital Converters
- 4. Circuit Symbol and Pin Identification 2 Inverting Input 3 Non-Inverting Input 6 Output 7 + Voltage Supply VCC 4 – Voltage Supply VEE 1 and 5 -- Offset Null U1 741 3 2 4 7 6 51
- 5. What do they really look like?
- 6. IC Circuit
- 7. Op-Amp “Golden Rules” • When an op-amp is configured in any negative- feedback arrangement, it will obey the following two rules: – The inputs to the op-amp draw or source no current (true whether negative feedback or not) – The op-amp output will do whatever it can (within its limitations) to make the voltage difference between the two inputs zero
- 10. Summing Circuits • Used to add analog signals • Voltage averaging function into summing function Calculate closed loop gain for each input 1 1 R R A f CL 2 1 R R A f CL 3 1 R R A f CL CLnino AVV 3 3 2 2 1 1 R R V R R V R R VV fff o 321 VVVVo If all resistors are equal in value:
- 11. Difference Circuit • Used to subtract analog signals • Output signal is proportional to difference between two inputs 12 VVVout If all resistors are equal: 1 31 124 4132 )( R RV RRR RRRV Vout
- 12. Integrating Circuit • Replace feedback resistor of inverting op-amp with capacitor • A constant input signal generates a certain rate of change in output voltage • Smoothes signals over time
- 13. Differentiating Circuit • Input resistor of inverting op- amp is replaced with a capacitor • Signal processing method which accentuates noise over time • Output signal is scaled derivative of input signal
- 14. Comparator Circuit • Determines if one signal is bigger than another • No negative feedback, infinite gain and circuit saturates • Saturation: output is most positive or most negative value V1 is Vref V2 is Vin
- 15. Analog to Digital Converters An electronic integrated circuit which transforms a signal from analog (continuous) to digital (discrete) form. Microprocessors can only perform complex processing on digitized signals. When signals are in digital form they are less susceptible to the deleterious effects of additive noise. ADC Provides a link between the analog world of transducers and the digital world of signal processing and data handling. Some examples of ADC usage are digital volt meters, cell phone, thermocouples, and digital oscilloscope.
- 16. How ADC works ? Mainly there are two steps for the analog to digital conversion: S/H: Sampling and holding Q/E: Quantizing and Encoding The ADC process is shown in figure below:
- 17. Sampling & Holding • It is used to sample the given input signal and to hold the sampled value. Once a signal is sampled, it is called a discrete signal. • Sample and hold circuit is used to sample an analog signal for a short interval of time in the range of 1 to 10µS and to hold on its last sampled value until the input signal is sampled again. • The holding period may be from a few milliseconds to several seconds.
- 18. Quantization and Encoding The output of a sampler is still continuous in amplitude. To transmit as a digital signal we must restrict the number of possible values. Quantization is the process of “rounding off” a sampled value according to some rule. – E.g. suppose we must round to the nearest tenth, then: 3.752 --> 3.8 0.001 --> 0 Encoding: After identifying the closest value, a numerical value is assigned to it and it is encoded in the form of a binary number.