Practical Electronics/Operating amplifiers

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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

V_o = A (V₂ - V₁)

Op Amp has an Integrated Circuit of electronic coponents inside a chip of 8 pins

Operational Amplifier IC Chip

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

Op Amp 's symbol

V₊: non-inverting input
V₋: inverting input
V_out: output
V_S+: positive power supply
V_S−: 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 = +V_ss

V₂ < V₁ , V₀ = -V_ss

V₂ = V₁ , V₀ = 0

[edit] Linear Configurations

[edit] Differential amplifier

Differential amplifier

$V_\mathrm{out} = V_2 \left( { \left( R_\mathrm{f} + R_1 \right) R_\mathrm{g} \over \left( R_\mathrm{g} + R_2 \right) R_1} \right) - V_1 \left( {R_\mathrm{f} \over R_1} \right)$

Differential $Z in$ (between the two input pins) = $R 1 + R 2$

[edit] Voltage Difference Amplifier

Whenever $R 1 = R 2$ and $R f = R g$ ,

$V_\mathrm{out} = {R_\mathrm{f} \over R_1} \left( V_2 - V_1 \right)$

[edit] Voltage Difference

When $R 1 = R f$ and $R 2 = R g$ (including previous conditions, so that $R 1 = R 2 = R f = R g$ ):

$V_\mathrm{out} = V_2 - V_1 \,\!$

[edit] Inverting Amplifier

Inverting amplifier

$V_\mathrm{out} = - V_\mathrm{in} \left( {R_f \over R_1} \right)$

Inverting Amplification is dictated by the ratio of the two resistors

[edit] Non-Inverting Amplifier

Non-inverting amplifier

$V_\mathrm{out} = V_\mathrm{in} \left( 1 + {R_2 \over R_1} \right)$

Non-Inverting Amplification is dictated by the ratio of the two resistors plus one

[edit] Voltage Follower

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

$V_\mathrm{out} = V_\mathrm{in} \!\$

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

$V_\mathrm{out} = - V_\mathrm{in} \!\$

[edit] Summing amplifier

Summing amplifier

$V_\mathrm{out} = - R_\mathrm{f} \left( { V_1 \over R_1 } + { V_2 \over R_2 } + \cdots + {V_n \over R_n} \right)$

When $R_1 = R_2 = \cdots = R_n$ , and $R f$ independent

$V_\mathrm{out} = - \left( {R_\mathrm{f} \over R_1} \right) (V_1 + V_2 + \cdots + V_n ) \!\$

When $R_1 = R_2 = \cdots = R_n = R_\mathrm{f}$

$V_\mathrm{out} = - ( V_1 + V_2 + \cdots + V_n ) \!\$

[edit] Integrator

Integrating amplifier

Integrates the (inverted) signal over time

$V_\mathrm{out} = \int_0^t - {V_\mathrm{in} \over RC} \, dt + V_\mathrm{initial}$

(where $V in$ and $V out$ are functions of time, $V initial$ is the output voltage of the integrator at time t = 0.)

[edit] Differentiator

Differentiating amplifier

Differentiates the (inverted) signal over time.

The name "differentiator" should not be confused with the "differential amplifier", also shown on this page.

$V_\mathrm{out} = - RC \left( {dV_\mathrm{in} \over dt} \right)$

(where $V in$ and $V out$ are functions of time)

[edit] Comparator

Comparator

$V_\mathrm{out} = \left\{\begin{matrix} V_\mathrm{S+} & V_1 > V_2 \\ V_\mathrm{S-} & V_1 < V_2 \end{matrix}\right.$

Từ V₀ = A (V₂ - V₁)

V_o = 0 khi V₂ = V₁

V_o > 0 khi V₂ > V₁

V_o = V_ss

V_o < 0 khi V₂ < V₁

V_o = 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

V_o = V_ss khi V₂ > V₁
V_o = V_-ss khi V₂ < V₁

[edit] Instrumentation amplifier

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

Schmitt trigger

A comparator with hysteresis

Hysteresis from $\frac{-R_1}{R_2}V_{sat}$ to $\frac{R_1}{R_2}V_{sat}$ .

[edit] Gyrator

Inductance gyrator

L = R_LRC

[edit] Zero level detector

Voltage divider reference

Zener sets reference voltage

[edit] Negative impedance converter (NIC)

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:

$R_\mathrm{in} = - R_3 \frac{R_1}{R_2}$

[edit] Non-linear configurations

[edit] Chỉnh Lưu

Super diode

Behaves like an ideal diode for the load, which is here represented by a generic resistor $R L$ .

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

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

Logarithmic configuration

The relationship between the input voltage $v in$ and the output voltage $v out$ is given by:

$v_\mathrm{out} = -V_{\gamma} \ln \left( \frac{v_\mathrm{in}}{I_\mathrm{S} \cdot R} \right)$

where $I S$ 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:

$\frac{v_\mathrm{in}}{R} = I_\mathrm{R} = I_\mathrm{D}$

where $I D$ is the current through the diode. As known, the relationship between the current and the voltage for a diode is:

$I_\mathrm{D} = I_\mathrm{S} \left( e^{\frac{V_\mathrm{D}}{V_{\gamma}}} - 1 \right)$

This, when the voltage is greater than zero, can be approximated by:

$I_\mathrm{D} \simeq I_\mathrm{S} e^{V_\mathrm{D} \over V_{\gamma}}$

Putting these two formulae together and considering that the output voltage $V out$ is the inverse of the voltage across the diode $V D$ , the relationship is proven.

Note that this implementation does not consider temperature stability and other non-ideal effects.

[edit] Exponential output

Exponential configuration

The relationship between the input voltage $v in$ and the output voltage $v out$ is given by:

$v_\mathrm{out} = - R I_\mathrm{S} e^{v_\mathrm{in} \over V_{\gamma}}$

where $I S$ 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:

$I_\mathrm{D} = I_\mathrm{S} \left( e^{\frac{V_\mathrm{D}}{V_{\gamma}}} - 1 \right)$

when the voltage is greater than zero, it can be approximated by:

$I_\mathrm{D} \simeq I_\mathrm{S} e^{V_\mathrm{D} \over V_{\gamma}}$

The output voltage is given by:

$v_\mathrm{out} = -R I_\mathrm{D}\,$

Practical Electronics/Operating amplifiers

From Wikibooks, the open-content textbooks collection

Contents

[edit] Intro

[edit] Op Amp Functions

[edit] Voltage Difference Amplifier

[edit] Voltage Comparator

[edit] Linear Configurations

[edit] Differential amplifier

[edit] Voltage Difference Amplifier

[edit] Voltage Difference

[edit] Inverting Amplifier

[edit] Non-Inverting Amplifier

[edit] Voltage Follower

[edit] Summing amplifier

[edit] Integrator

[edit] Differentiator

[edit] Comparator

[edit] Instrumentation amplifier

[edit] Schmitt trigger

[edit] Gyrator

[edit] Zero level detector

[edit] Negative impedance converter (NIC)

[edit] Non-linear configurations

[edit] Chỉnh Lưu

[edit] Peak detector

[edit] Logarithmic output

[edit] Exponential output

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