Differentiator amplifier, also known as a differentiating amplifier or a differentiator circuit, is an operational amplifier in which output voltage is directly proportional to the input’s time derivative.
In simpler words, the output voltage can be modified based on the time derivative or the RC time constant. The RC constant is the product of the circuit resistance and capacitance. Therefore, we can modify the resistor-capacitor combination to obtain the desired differentiating amplification.
Essentially, a differentiator amplifier functions as a high-pass filter. For instance, it can generate an output of square waves when programmed an input of triangular waves. These circuits are quintessential to analog computers, PID controllers as well as in frequency modulators.
Explaining The Op-Amp Differentiator Circuit
As can be seen in the circuit diagram, the input signal is applied to the capacitor. Afterward, the capacitor, as it should, blocks the DC content which means there’s no current to flow. The output voltage at this point is zero.
However, the capacitor forwards the AC input voltage. The frequency of this voltage is dependent on the input signal’s rate of change.
Lower frequencies mean the capacitor reactance is high which results in a low gain. However, higher frequencies yield lower capacitor reactance which results in a higher gain and subsequently, a higher output voltage.
It’s also worth mentioning that high frequencies can also lead the differentiator amplifier to become unstable. At higher frequencies, the differentiator will begin to oscillate. Other than the oscillation, one drawback is susceptibility to noisy signals. Since the input is capacitive, any noise present in the source will also be amplified.
Differentiating Waveforms
Square waves, sine waves, and triangular waves are classified as constantly changing signals. When such signals are applied to the input of any differentiator amplifier circuit, the output we receive is also changed.
The output waveform depends greatly on the RC time constant, as discussed before. So if a square wave input is applied, the output will be voltage spikes. On the other hand, triangular waves will be converted into rectangular ones. Sine waves are also transformed into cosine waves.
Overcoming The Flaws
As discussed before, the basic differentiator has two glaring flaws of instability and noise amplification. For this reason, the basic circuit isn’t widely used. However, this can be overcome by improving the differentiator amplifier. How? By adding an extra input resistance.
The addition of input resistance limits the increase in gain. Now, the circuit works as a differentiator amplifier at lower frequencies. At higher frequencies, it functions as an amplifier offering resistive feedback, leading to better noise rejection.
Apart from differentiator amplifiers, ADSANTEC also offers other products such as a linear amplifier, a limiting transimpedance amplifier, pre-emphasis amplifier and a limiting amplifier. Contact now to find out more about how we can fulfill your electronic circuit needs!