One realization of absolute value amplifier with op-amp and one diode is given in figure bellow.

Simulate op-amp absolute value amplifier.

In order to analyze given circuit, analysis has to be separated.

**V**>_{IN}**0**.

If input voltage is positive, inverting input of **OP _{1}** is on higher potential then non-inverting input which is on the ground level. It means that output of

**OP**is negative, i.e. anode of the diode

_{1}**D**is negative. Cathode of the diode

**D**is on positive

**V**level, so diode

_{IN}**D**is inverse biased. Equivalent circuit is given in figure bellow.

Now, non-inverting input of **OP _{2}** is connected via

**R**to

_{3}**V**. Inverting input is also connected to

_{IN}**V**via

_{IN}**2R**. Both inputs are on the same potential,

_{1}**OP**operates in amplifying mode, and inverting input is shortly connected to the output. If

_{2}**V**>0,

_{IN}**V**=

_{OUT}**V**.

_{IN}

**V**_{IN}<0

If input voltage is negative, inverting input of **OP _{1}** is on lower potential then non-inverting input which is on the ground level. It means that output of

**OP**is positive, i.e. anode of the diode

_{1}**D**is positive. Cathode of the diode

**D**is on negative

**V**level, so diode

_{IN}**D**is forward biased. Equivalent circuit is given in figure bellow.

Now, inverting input of **OP _{1}** is on the virtual ground, i.e. on potential of zero volts (which was not the case when input was positive). Current through

**R**flows from point

_{1}**A**(zero volts) to input terminal (negative voltage). Current through

**R**is with the same magnitude and since

_{2}**R**=

_{1}**R**, potential of point

_{2}**B**is positive and equal to

**â€“V**. Non-inverting input is on the same positive potential of

_{IN}**â€“V**. Inverting input of

_{IN}**OP**is shortly connected to output, so output now is

_{2}**â€“V**. If

_{IN}**V**>0,

_{IN}**V**=

_{OUT}**-V**.

_{IN}Go to op-amp absolute value amplifier simulation.

**External links:**

Our video tutorial about op-amp absolute value amplifier

Op-amp absolute value amplifier on edn

Op-amp absolute value amplifier on westhost

Op-amp absolute value amplifier on electronics.stackexchange

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