Practical Electronics/Operational amplifiers

Intro Op Amp is a short hand term for Operational Amplifier. An operational amplifier is a circuit component that amplifies the difference of two input voltages: Vo = A (V2 - V1) Op Amps are usually packaged as an 8-pin integrated circuit. thumb|right|Operational Amplifier IC Chip Pin Usage 1 Offset Null 2 Inverted Input 3 Non-Inverted Input 4 -V Supply 5 No use 6 Output 7 +V Supply 8 No use Op Amp symbol thumb|200px|op-amp V+: non-inverting input V−: inverting input Vout: output VS+: positive power supply VS−: negative power supply Op amps amplify AC signal or AC Voltage better than a simple bipolar junction transistor. Op Amp Functions Voltage Difference Amplifier From above V0 = A (V2 - V1) Voltage Comparator V2 > V1 , V0 = +Vss V2 < V1 , V0 = -Vss V2 = V1 , V0 = 0 Inverting Amplifier With one voltage is grounded If V2 = 0 , V0 = -A V1 . Inverting Amplifier Non-Inverting Amplifier With one voltage is grounded If V1 = 0 , V0 = A V2 . Non-Inverting Amplifier Linear Configurations Differential amplifier thumb|Differential amplifier Differential (between the two input pins) = Voltage Difference Amplifier Whenever and , Voltage Difference When and (including previous conditions, so that ): Inverting Amplifier thumb|Inverting amplifier Inverting Amplification is dictated by the ratio of the two resistors Non-Inverting Amplifier thumb|Non-inverting amplifier Non-Inverting Amplification is dictated by the ratio of the two resistors plus one Voltage Follower thumb|Voltage follower From Non-Inverting Amplifier's formula. If the resistors has the same value of resistance then output voltage is exactly equal to the input voltage From Inverting Amplifier's formula. If the resistors has the same value of resistance then output voltage is exactly equal to the input voltage and inverted Summing amplifier thumb|Summing amplifier When , and independent When Integrator thumb|Integrating amplifier Integrates the (inverted) signal over time (where and are functions of time, is the output voltage of the integrator at time t = 0.) Differentiator thumb|Differentiating amplifier Differentiates the (inverted) signal over time. The name "differentiator" should not be confused with the "differential amplifier", also shown on this page. (where and are functions of time) Comparator thumb|Comparator Từ V0 = A (V2 - V1) Vo = 0 khi V2 = V1 Vo > 0 khi V2 > V1 Vo = Vss Vo < 0 khi V2 < V1 Vo = V-ss When two input voltages equal. The output voltage is zero . When the two input voltages different and if one is greater than or less than the other Vo = Vss khi V2 > V1 Vo = V-ss khi V2 < V1 Instrumentation amplifier thumb|Instrumentation amplifier Combines very high input impedance, high common-mode rejection, low DC offset, and other properties used in making very accurate, low-noise measurements Is made by adding a inverting buffer to each input of the differential amplifier to increase the input impedance. Schmitt trigger thumb|Schmitt trigger A comparator with hysteresis Hysteresis from to . Gyrator thumb|Inductance gyrator A gyrator can transform impedances. Here a capacitor is changed into an inductor. Zero level detector Voltage divider reference Zener sets reference voltage Negative impedance converter (NIC) thumb|Negative impedance converter Creates a resistor having a negative value for any signal generator In this case, the ratio between the input voltage and the input current (thus the input resistance) is given by: Non-linear configurations Rectifier thumb|Super diode Behaves like an ideal diode for the load, which is here represented by a generic resistor . This basic configuration has some limitations. For more information and to know the configuration that is actually used, see the main article. Peak detector thumb|Peak detector When the switch is closed, the output goes to zero volts. When the switch is opened for a certain time interval, the capacitor will charge to the maximum input voltage attained during that time interval. The charging time of the capacitor must be much shorter than the period of the highest appreciable frequency component of the input voltage. Logarithmic output thumb|Logarithmic configuration The relationship between the input voltage and the output voltage is given by: where is the saturation current. If the operational amplifier is considered ideal, the negative pin is virtually grounded, so the current flowing into the resistor from the source (and thus through the diode to the output, since the op-amp inputs draw no current) is: where is the current through the diode. As known, the relationship between the current and the voltage for a diode is: This, when the voltage is greater than zero, can be approximated by: Putting these two formulae together and considering that the output voltage is the inverse of the voltage across the diode , the relationship is proven. Note that this implementation does not consider temperature stability and other non-ideal effects. Exponential output thumb|Exponential configuration The relationship between the input voltage and the output voltage is given by: where is the saturation current. Considering the operational amplifier ideal, then the negative pin is virtually grounded, so the current through the diode is given by: when the voltage is greater than zero, it can be approximated by: The output voltage is given by: cs:Praktická elektronika/Operační zesilovače