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The matching capacitor is added to make the receiver detect the frequency range in the 1—10 kHz range. In normal operation, the noise level reaches 10 nV level, which not only increases the stability of the circuit, but also reduces the noise of the sensor. It has far-reaching significance for the detection of weak frequency signals. Keywords: frequency-domain electromagnetic method, coil sensor, low noise, amplification circuit 1. Introduction The frequency domain electromagnetic method is widely used in resource exploration and geological structure detection [ 1 ].
The semi-aviation frequency domain electromagnetic detection method can radiate alternating electromagnetic waves in earth and space by arranging an electric long wire source on the ground and outputting an alternating current to earth.
During the electromagnetic wave propagation process, when there is an abnormal change in the electrical structure in the local area, the amplitude and phase of the propagation path and the electromagnetic field will also change accordingly. The receiving system collects signals in the air, and by identifying the abnormalities at different frequencies, information such as the position, depth, and size of the abnormal body can be determined.
However, there is currently no commercial inductive magnetic sensor for the semi-aeronautical frequency domain electromagnetic detection system, so the development of magnetic sensors used in this field has an important role and significance. Existing magnetic sensors for electromagnetic detection mainly include magnetic core rods and air-core coil sensors. Since the magnetic rod has a ferromagnetic core, the sensitivity is high, and it is easy to saturate when moving in the air, so the air-core is applied.
The coil sensor performs semi-aero frequency domain electromagnetic detection. Air-core coil sensors are widely used in electromagnetic detection. That means how much the output is going back to the input of the amplifier. As the amplifier is unity gain amplifier, the feedback factor is 1 hence all of the output can be considered as going back to the input. The above image is a representation of the formula and negative feedback amplifier circuit. It is exactly identical with the traditional negative amplifier stated previously.
They both share AC input on the positive terminal, and both have the same feedback in the negative terminal. The circle is the summing junction has two inputs, one from the input signal and the second one from the feedback circuit. Well, when the amplifier is working in negative feedback mode, the complete output voltage of the amplifier is flowing through the feedback line to the summing junction point. At the summing junction, feedback voltage and the input voltage is added together and feeded back into the input of the amplifier.
The image is divided into two gain stage. Firstly, it is showing complete closed-loop circuit as this is a closed-loop network and also the op-amps open-loop circuit because the op-amp showing A is a standalone open circuit, the feedback is not directly connected. The output of the summing junction is further amplified by the op-amp open-loop gain.
But the closed-loop gain is limited as the power supply which is connected across the op-amp is limited hence the Amplifier will become unstable. Now, for a negative feedback amplifier, the phase shift of the input and output is degrees. When a capacitive load is connected across the amplifier, it can alter the phase by adding an additional pole across the op-amp output resulting in a negative to positive feedback conversion. The loop gain gets 1 at the degree phase shift and induces instability.
Instability of the amplifier provides poor phase margin and hampered slew rate which results in an unnatural behavior across the op-amp output. The output oscillates and creates ringing effects when switching the output state. Since practically there are no ideal loads, resistive loads are not ideally resistive even perfectly made circuits have lots of capacitance as well as inductance.
The outcome is poor phase response at high frequency and instability. How to deal with Op-Amp Instability? The solution is not a straightforward way. The Solution is to provide frequency compensation to the op-amp. This is a useful technique to overcome the instability of the op-amp as well as improve the step response of the circuit. Types of Op-Amp Frequency Compensation There are different types of frequency compensation techniques used in electronics.
However, all techniques are categorized into two basic types of compensation technique. The first one is external compensation across the op-amp and the second one is the internal compensation technique. External Frequency Compensation in Op Amp External compensation techniques vary depending on the application, type of amplifier used and many other things.
The easiest way is to use out-of loop compensation technique or in-loop compensation technique. Out of the loop compensation technique uses a simple resistor to isolate the capacitive load with the op-amp, lowering the capacitive loading of the op-amp.
The resistor typically varies from Ohms but the increase in isolated resistor effects the op-amp bandwidth. The bandwidth of the op-amp drastically reduced to a very low value. One of the popular ways of out of the loop frequency compensation techniques is to use Dominant pole compensation technique. Dominant pole Compensation This technique uses a simple RC network connected across the output of the operational amplifier circuit.
A sample dominant pole compensation circuit is shown below. This works great to overcome the instability issue. The RC network creates a pole at unity or 0dB gain that dominates or cancels out other high-frequency poles effect. The Bode plot below shows what happens if the dominant pole compensation technique is added across the op-amp output, where fd is the dominant pole frequency.
Miller compensation Another effective compensation technique is the miller compensation technique and it is an in-loop compensation technique where a simple capacitor is used with or without load isolation resistor Nulling resistor. That means a capacitor is connected in the feedback loop to compensate the op-amp frequency response.
The miller compensation circuit is shown below. In this technique, a capacitor is connected to the feedback with a resistor across the output. The circuit is a simple negative feedback amplifier with inverting gain dependent on R1 and R2.
The R3 is the null resistor and the CL is the capacitive load across the op-amp output. CF is the feedback capacitor which is used for the compensation purposes. The Capacitor and the resistor value depend on the type of amplifier stages, pole compensation, and the capacitive load. Internal Frequency Compensation Techniques Modern operational amplifiers have internal compensation technique.
In the internal compensation technique, a small feedback capacitor is connected inside of the op-amp IC between the second stages Common emitter transistor. For example, the below image is the internal diagram of popular op-amp LM The Cc capacitor is connected across the Q5 and Q It is the compensation Capacitor Cc. This compensation capacitor improves the stability of the amplifier and as well as prevent the oscillation and ringing effect across the output.
This op-amp does not have any compensation capacitor inbuilt.
Rf is the feedback resistor. Non inverting input of the opamp is grounded using resistor Rm. RL is the load resistor. Scaling amplifier : In a scaling amplifier each input will be multiplied by a different factor and then summed together. Scaling amplifier is also called a weighted amplifier. Here different values are chosen for Ra, Rb and Rc. Summing amplifier in non inverting configuration.
Summing amplifier in non inverting configuration A non inverting summing amplifier circuit with three inputs are shown above. In this circuit configuration, the output voltage signal is given to the inverting terminal - of the operational amplifier like feedback through a resistor where another resistor is given to the ground. Here, a voltage divider with two types of resistors will provide a small fraction of the output toward the inverting pin of the operational amplifier circuit.
Non-Inverting Op-Amp Circuit These two resistors will provide necessary feedback to the operational amplifier. Here, the R1 resistor is called a feedback resistor Rf. Because of this, the Vout depends on the feedback network. The Current rule states that there is no flow of current toward the inputs of an op-amp whereas the voltage rule states that the op-amp voltage tries to ensure that the voltage disparity between the two op-amp inputs is zero. From the above non-inverting op-amp circuit, once the voltage rule is applied to that circuit, the voltage at the inverting input will be the same as the non-inverting input.
So the applied voltage will be Vin. Therefore the non-inverting op-amp will generate an amplified signal that is in phase through the input. Input Impedance In a non-inverting operational amplifier circuit, the input impedance Zin can be calculated by using the following formula.
AdSave Time and Money by Searching Today with Findchips. Compare a Huge Selection of casino1xbetbonuses.website electronic parts · Reliable and easy to use · Compare component prices. 11/11/ · A non inverting summing amplifier circuit with three inputs are shown above. The voltage inputs Va, Vb and Vc are applied to non inverting input of the opamp. Rf is the feedback resistor. The output voltage of the circuit is governed by the equation; Vo = . Non-inverting Op-amp calculator Op-amp Gain Entering a value for Gain will find the optimum values for R1 and R2. If you specify the values for R1 and R2, the gain is found. If you enter a resistor values (R1 or R2) along with the gain, the other value will be found. The circuit configuration shown is a non-inverting amplifier.