Why precision rectifier

Since the output from the Point P2 is fed directly to the summing amplifier with the gain of 2X, that means the output voltage will be 2-times the input voltage.

Let's assume the input voltage is 2V peak, so we will get a 4V peak at the output. At the same time, we are directly feeding the input to the summing amplifier with a gain of 1X.

The above image shows the final output of the circuit, the waveform in blue is the Input and the waveform in Yellow is the output from the half-wave rectifier circuit , and the waveform in green is the output of the full-wave rectifier circuit.

Circuit diagram for half-wave and full-wave precision rectifier using op-amp is given below:. For this demonstration, the circuit is constructed in a solderless breadboard, with the help of the schematic; To reduce parasitic inductance and capacitance, I have connected the components as close as possible.

The circuit can be further modified in order to improve its performance like we can add an additional filter in order to reject high-frequency noises. This circuit is made just for demonstration purposes only. If you are thinking about using this circuit in a practical application, you have to use a chopper type op-amp and high precision 0. I hope you liked this article and learned something new out of it. If you have any doubt, you can ask in the comments below or can use our forums for detailed discussion.

Well explained Debashis, but look at the part where you mention. There are no such resistors! For someone familiar with how op-amps work, this is not difficult to figure out, but your description needs to be consistent with component names used. Yes you are right. Thank you. Get Our Weekly Newsletter!

Helena St. Related Content. The reason is just that in several applications the signal we would like to fix will be less than the voltage required to activate a diode. Even small-signal Ge germanium diodes require about 0.

This can be solved by using a precision rectifier. This article discusses precision rectifier using LT The precision rectifier or super diode is an arrangement achieved with one or more op-amps operational amplifiers in order to have a circuit perform like a rectifier and an ideal diode. Circuit designers have two standard methods for designing a precision rectifier.

They can amplify the AC signal and then rectify it, or they can do both at once with a single operational amplifier. The latter method is often considered a much better way to get the job done. The outputs of the two rectifiers are then joined to a common load. This idea is described in figure 5. The waveforms at various nodes are also shown in the same figure. A practical circuit can be obtained from figure 5 by replacing diode D A with a super diode and by replacing diode D B and the inverting precision half-wave rectifier but without the catching diode.

The actual circuit of a precision full-wave rectifier of this kind is shown in figure 6. Lets see how the circuit of figure 6 operates: Consider the case of a positive input at A. The output of A2 will go positive, turning D2 on, which will conduct through R L and thus close the feedback loop around A2. Thus, a short circuit will established between the two input terminals of A2.

At the same time, the voltage at the inverting input terminal of A2, which is the output voltage of the circuit, will become equal to the input. Thus no current will flow through R1 and R2, and the voltage at the inverting input of A1 will be equal to the input and hence positive.

Therefore the output terminal C of A1 will go negative until A1 saturates. This causes D1 to be turned off. Next consider what happens when A goes negative. The tedency for a negative voltage at the input of A1 causes C to rise, making D1 conduct to supply R L and allowing the feedback loop around A1 to be closed. Thus a virtual ground appears at the inverting input of A1, and the two equal resistors R1 and R2 force the voltage at C, which is the output voltage, to be equal to the negative of the input voltage at A and thus positive.

The combination of positive voltage at C and negative voltage at A causes the output of A2 to saturate in the negative direction, thus keeping D2 off. The overall result is perfect full wave reactification, as represented by the transfer characteristic in figure 6. The precision is a result of placing the diodes in op-amp feddback loops, thus masking their nonidealities.

The circuit of figure 6 is one of many possible precision ful-wave rectifiers or absolute-value circuits. A full wave precision rectifier can be made also by using a diode bridge. One such arrangement is shown in figure 7. This circuit can be useful for instrumentation applications because it can provide a balanced output on R L and, also a relative accurate high-input impedance.

Thus, the current or the differential voltage in R L 's terminals is propotional to the absolute value of the input voltage u i. All the nonidealities of the diodes are masked by placing the bridge circuit in the negative-feddback loop of the op-amp.

Thus the feedback loop remains closed for both polarities of u i. The resulting short circuit at the input terminals of the op-amp causes a replica of u i to appear across R.

You are here: Home Lessons Precision rectifiers explained. It may not display this or other websites correctly. You should upgrade or use an alternative browser. Why is precision rectifier called this way? Thread starter sayurabh Start date May 5, Status Not open for further replies.

Re: precision rectifrier Actualy with transformer you dont get good output voltage, cause diodes on output your input voltage must rise enough to drive those diodes That is not case with opamp, because as soon as input voltage is positive you have output voltage that is just amped input voltage Re: precision rectifrier A normal rectifier add a 0. The feedback loop in the precision rectifier avoid this drop.

Meridian Full Member level 5. Re: precision rectifrier sayurabh said:. Click to expand Kral Advanced Member level 4. Re: precision rectifrier sayurabh, A precision rectifier typically has the diode s inside the feedback loop.