š Electronics Competition Created by: Type Tahmeeed zz Notes Explain the process of an electronic sensor Deļ¬ne an operational ampliļ¬er (Op-amp) A device which is integrated into circuits to produce an ampliļ¬cation or gain to the voltage (A) Explain the circuit symbol for an op-amp Electronics 1 V+ = plus input (‘non-inverting’ input) (V) V- = minus input (‘inverting’ input) (V) Vout= output voltage (V) Vs+ = positive voltage of the power supply (V) Vs- = negative voltage of the power supply (V) State the equation of Vout What are the characteristics of an ideal operational ampliļ¬er Inļ¬nite input resistance (no current from the supply) Inļ¬nite open-loop gain (AOL) (gain obtained when no overall feedback is used) Zero output resistance (no ‘lost volts’ when current is supplied) Inļ¬nite bandwidth (an ideal op-amp will amplify signals of all frequencies) Inļ¬nite slew rate (changes in output are instantaneous to changes in input – no time delay between the two) Whats the function of op-amp To use the potential differences between two inputs V+ and V− to produce a large output Vout as possible Suggest some properties of op-amp High gain (A = 10^5 – 10^6) Used for feedback circuits Electronics 2 Has a differential input (output voltage Vout is proportional to the difference in V+ and V- input signals) How can an ideal Op-amp can be used to compare two voltages When the two voltages are equal, Vout is 0 It can compare V+ and V- and tell which one is larger This is because an ideal op-amp has inļ¬nite resistance Deļ¬ne Negative feedback of an op-amp Part of output signal is added to input signal and the output is out of phase with the input by 180° How can one make the feedback negative Attach to the negative (inverting input) terminal of an op-amp closed-loop gain is produced due to the closed-loop circuit What are the effects of negative feedback on the gain on an op-amp Reduced gain Increased bandwidth or less distortion Increase operating stability What are the two types of ampliļ¬ers? inverting ampliļ¬er non-inverting ampliļ¬er Explain what is an Inverting ampliļ¬er? An inverting ampliļ¬er uses negative feedback The non-inverting input is connected to the 0 V (ground) line This means there is 0 V in the non-inverting and inverting terminal Part of Vout is connected to the inverting input The input voltage is connected to the inverting input Electronics 3 current in the input resistor is Iin and the current in the feedback resistor is If Explain what is an Non-inverting ampliļ¬er? The input voltage is connected to the non-inverting input Part of Vout is fed back to the inverting input What is meant by virtual earth? op-amp has inļ¬nite gain non inverting input is at 0V 0 V same potential as inverting input What are the approximations of a virtual earth in an Inverting Ampliļ¬er? An op-amp has a very large open-loop voltage gain V+ is at earth potential (0 V) If the ampliļ¬er is not to saturate, V= input must be almost at earth potential too Electronics 4 State an equation and the derivation of gain of the inverting ampliļ¬er (A) If V− = 0 V (Earth potential) Rin is very high so virtually no current enters or leaves the inverting input hence A = gain Vout = output voltage (V) Vin= input voltage (V) Rf = feedback resistance (Ω) Rin= input resistance (Ω) State an equation for non-inverting ampliļ¬ers Both resistors form a potential divider Rf = feedback resistance (resistance of resistor connected to the ampliļ¬er) R = additional resistor Describe Calibration of Digital and Analogue Meters Calibration is needed because op-amp voltage not proportional to measured physical quantity For digital: temperature sensor and a thermometer is placed in water bath over a range of temperatures and voltmeter reading is changed using Electronics 5 calibration curve giving rise to a scale For analogue: The same process but linearity of scale will change Deļ¬ne relay in an electronic circuit A device which switches the mains supply on or off using a low voltage output consists of an electromagnetic switch operated by a small current in the coil to convert a small electrical input to a higher current output What are the 2 types of relay and describe each Normally open (NO): When the relay is activated, the contacts connect the circuit (like closing a switch) and the circuit is disconnected when the relay is inactive Normally Closed: relays disconnect the circuit when the relay is activated, and the circuit is connected when the relay is inactive What is an light-emitting Diodes (LED) and describe its use A type of semiconductor diode that emits light when current slows in a speciļ¬c direction Helps indicating the state of an output in electronic circuits State the function of comparator To compare two voltages Output depends upon which is greater Electronics 6 Note: Remember that LEDs will emit light when they are forward biased in the same direction as conventional current ļ¬ow (positive to negative) and will not emit light when in the opposite direction to the current ļ¬ow Electronics 7
