Op Amp Differentiator
Op Amp Differentiator
The Operational Amplifier or Op-Amp is a linear system used for ideal DC amplification, signal conditioning, filtering and mathematical operations such as addition, subtraction, integration and differentiation. Op-amp is a voltage amplifier that has external feedback elements between output and input terminals, such as capacitors and resistors. The feedback components provided in the Op-Amp are useful for working in an efficient manner. Op-Amp is a three-terminal system consisting of two high impedance inputs, i.e. inverting input and non-inverting input and one output port, and can be either current or voltage. This op-amp is primarily used to increase low signal levels. The Op-amp differentiator may be active or passive depending on the components used in the design. It's essentially a high pass filter, and we're going to use these different filters.
What is an Op Amp Differentiator?
The basic operational amplifier differentiator circuit generates the output signal, which is the first derivative of the input signal. Op amp differentiator is a circuit configuration that generates an output voltage amplitude that is proportional to the rate of change of the input voltage. This means that when the input voltage signal is changed, the output voltage will change automatically.
Op amp differentiator simple A differentiator circuit is one in which the output of the voltage is directly proportional to the rate of change of the input voltage with respect to time. This means that the more the input voltage signal increases, the higher the output voltage changes in the response.
Working of Op Amp Differentiator
The input signal to the differentiator is applied to the capacitor. The capacitor blocks any DC content so there is no current flow to the amplifier summing point, X, resulting in zero output voltage. The capacitor only allows AC type input voltage changes to pass through and whose frequency is dependent on the rate of change of the input signal. At low frequencies, the capacitor's reactivity is "high" resulting in a low output ( Rƒ/Xc ) and a low output voltage from the op-amp. At higher frequencies, the capacitor's response is much smaller, resulting in higher gain and higher output voltage from the differentiator amplifier. However the Op-amp differentiator circuit becomes erratic at high frequencies and begins to oscillate. This is mainly due to the first-order effect, which determines the frequency response of the op-amp circuit resulting in a second-order response which at high frequencies, gives an output voltage much higher than expected. In order to prevent this the high-frequency gain of the circuit needs to be minimised by adding an additional small-value capacitor to the feedback resistance of Rƒ. Ok, some math to explain what’s going on!. Since the node voltage of the operational amplifier at its inverting input terminal is zero, the current, i flowing through the capacitor will be given as:
The charge on the capacitor equals Capacitance times Voltage across the capacitor
Thus the rate of change of this charge is:
but dQ/dt is the capacitor current, i
from which we have an ideal voltage output for the op-amp differentiator is given as:
As a consequence, the output voltage Vout is a constant –R+*C times the output voltage VIN derivative with respect to time. The minus sign (–) shows a 180o phase shift since the input signal is attached to the inverting input terminal of the working amplifier. The last thing to note is that the Op-amp differentiator circuit in its basic form has two key drawbacks relative to the previous working amplifier integrator circuit. One is that it suffers from high frequency instability as described above, and the other is that the capacitive input makes it very vulnerable to random noise signals, and any noise or harmonics present in the source circuit can be amplified rather than the input signal itself. It's how the output is additive.
Differentiator Circuit Output Waveform
Differential Amplifier Applications
- Very useful if you have two inputs corrupted with the same noise.
- Subtract one from the other to remove noise, remainder is signal.
- Many Applications : e.g. an electrocardiogram measures the potential difference between two points on the body.
- It is used as a series negative feedback circuit by using an op amplifier.
- Generally, we use a differential amplifier that acts as a volume control circuit.
- The differential operational amplifier can be used as an automatic gain control circuit.
- Some of the differential operational amplifiers can be used for Amplitude.
- Operational amplifiers can be used in construction of active filters, providing high pass, band pass reject and delay functions. The high input impedance, gain of an op-amp allow straightforward calculation of element values.