Practical Electronics/Operating amplifiers
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Contents
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[edit] Intro
Op Amp is short hand of Operational Amplifier . A tool used in amplifying the difference of two input voltages
-
- Vo = A (V2 - V1)
Op Amp has an Integrated Circuit of electronic coponents inside a chip of 8 pins
| Pin | Useage |
|---|---|
| 1 | Offset Null |
| 2 | Inverted Input |
| 3 | Non-Inverted Input |
| 4 | -V Supply |
| 5 | No use |
| 6 | Output |
| 7 | +V Supply |
| 8 | No use |
- V+: non-inverting input
- V−: inverting input
- Vout: output
- VS+: positive power supply
- VS−: negative power supply
Op Amp amplify AC signal or AC Voltage better than bipolar junction transistor
[edit] Op Amp Functions
[edit] Voltage Difference Amplifier
From above
-
- V0 = A (V2 - V1)
With two voltages V1 và V2 ≠ 0
- If V2 = V1 , V0 = 0 . No output voltage
- If V2 > V1 , V0 > 0 . Non-Inverting Amplifier
- Nếu V2 < V1 , V0 < 0 . Inverting Amplifier
With one voltage is grounded
- If V2 = 0 , V0 = -A V1 . Inverting Amplifier
- If V1 = 0 , V0 = A V2 . Non-Inverting Amplifier
[edit] Voltage Comparator
- V2 > V1 , V0 = +Vss
- V2 < V1 , V0 = -Vss
- V2 = V1 , V0 = 0
[edit] Linear Configurations
[edit] Differential amplifier
- Differential Zin (between the two input pins) = R1 + R2
[edit] Voltage Difference Amplifier
Whenever R1 = R2 and Rf = Rg,
[edit] Voltage Difference
When R1 = Rf and R2 = Rg (including previous conditions, so that R1 = R2 = Rf = Rg):
[edit] Inverting Amplifier
Inverting Amplification is dictated by the ratio of the two resistors
[edit] Non-Inverting Amplifier
Non-Inverting Amplification is dictated by the ratio of the two resistors plus one
[edit] 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
[edit] Summing amplifier
When
, and Rf independent
When 
[edit] Integrator
Integrates the (inverted) signal over time
(where Vin and Vout are functions of time, Vinitial is the output voltage of the integrator at time t = 0.)
[edit] Differentiator
Differentiates the (inverted) signal over time.
The name "differentiator" should not be confused with the "differential amplifier", also shown on this page.

(where Vin and Vout are functions of time)
[edit] 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
[edit] 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.
[edit] Schmitt trigger
A comparator with hysteresis
Hysteresis from
to
.
[edit] Gyrator
-
- L = RLRC
[edit] Zero level detector
Voltage divider reference
- Zener sets reference voltage
[edit] Negative impedance converter (NIC)
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:
[edit] Non-linear configurations
[edit] Chỉnh Lưu
Behaves like an ideal diode for the load, which is here represented by a generic resistor RL.
- This basic configuration has some limitations. For more information and to know the configuration that is actually used, see the main article.
[edit] 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.
[edit] Logarithmic output
- The relationship between the input voltage vin and the output voltage vout is given by:
where IS 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 ID 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 Vout is the inverse of the voltage across the diode VD, the relationship is proven.
Note that this implementation does not consider temperature stability and other non-ideal effects.
[edit] Exponential output
- The relationship between the input voltage vin and the output voltage vout is given by:
where IS 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:




















