Amplifier Distortion : Circuit, Types, How to Reduce and Vs Distortion Pedals

An amplifier is an electronic device that strengthens the input of a smaller signal to a larger o/p signal. So the output signal is changing continuously by some gain values. These are utilized within wireless communications & broadcasting in all kinds of audio equipment. In ideal conditions, the amplified o/p signal of the amplifier should have a similar waveform precisely to the input signal. However, this ideal condition is not at all achieved within practical amplifiers. Thus, some modifications within the waveform may occur additionally to the rise in the amplitude which is known as the distortion. It is unwanted because it may modify the intelligence carried through the signal. This article provides brief information on amplifier distortion, working, and its applications.

What is Amplifier Distortion?

Amplifier distortion can be defined as; any difference from the input signal of an amplifier that occurs throughout the amplification process and gives a changed output signal in terms of magnitude, shape, frequency content, etc. It occurs due to many factors like; non-linearity within the components of the amplifier, improper biasing, or amplifier overloading. The amplifier distortion is undesirable because it degrades the value of the amplified signal.

Amplifier Distortion Circuit

Amplifier distortion can be understood with an example of a common emitter (CE) amplifier circuit. The output signal distortion may happen because of the following reasons.

• Amplification may not occur over the complete signal cycle because of the wrong biasing levels.
• If the input signal is very large, then it causes the transistors of amplifiers to be limited through the voltage supply.
• The amplification cannot be a linear signal above the whole input frequency range which means during the signal waveform’s amplification procedure, Amplifier Distortion will occur.

Amplifiers are designed for amplifying small input voltage signals into larger output signals which means the output signal will be changed constantly by gain value which is multiplied with the input signal mainly for all input frequencies.

The following common emitter (CE) circuit operates for small input AC signals however it causes some troubles in their working. So, the intended position of the BJT amplifier’s biasing point ‘Q’ depends on the related Beta value for all types of transistors.

Common emitter-type transistor circuit works well mainly for small AC input signals although suffer from one main drawback, the calculated position of the bias Q-point of bipolar amplifier depends mainly on the related Beta value of all kinds of transistors. However, this beta value fluctuates from similar kinds of transistors that means, one transistor’s Q-point is not related to another transistor with a similar category because of the acceptances of characteristic productions. After that, amplifier distortion happens because the amplifier is not linear. Careful selection of the transistor & biasing components can assist in minimizing the amplifier distortion effect.

Types of Amplifier Distortion

There are different types of amplifier distortion which are discussed below. The distortion type mainly depends on the area of characteristics that are utilized by the transistor, the device reactance & the associated circuit.

Non-linear Distortion

Non-linear distortion mainly happens in an amplifier whenever the input signal applied is large & the active device is driven into a non-linear area of its characteristics. This distortion is used to describe a non-linear relationship between the input & output signals of an amplifier. So this distortion results from systems wherever the output signal is not proportional precisely to the input signal & intermodulation products or harmonics are generated.

Amplitude Distortion

Amplitude distortion is a type of nonlinear distortion that takes place because of the attenuation within the crest value of the signal. The shift within the Q point & amplification for below 360⁰ of the signal leads mainly to distortion in amplitude. This distortion mainly occurs because of clipping & incorrect biasing. We know that that if the transistor’s biasing point is correct, the output is similar to the input within the amplified shape. This can be understood through the following cases.

Suppose inadequate biasing is provided to the amplifier, then the Q-point will lie close to the minor half of the load line. So in this condition, the input signal’s negative half is clipped & we acquire a distorted output signal of the amplifier.

If we provide an additional bias potential, then the Q-point will be at the higher side of the load line. So this condition provides an output that will be cut off at the positive half of the waveform.
Proper biasing can also lead to distortion sometimes within the output in case the input signal is large because this input signal is amplified through the amplifier’s gain. So both the positive & negative half of the waveform will get clipped at some part which is called clipping distortion.

Linear Distortion

Linear distortion mainly occurs whenever the input signal applied to drive the device is small & functions in the linear section of its characteristics. So this distortion mainly happens because of active devices’ frequency-dependent characteristics.

Frequency Distortion

In this type of distortion, the amplification level changes in frequency. The input signal during amplification in a realistic amplifier includes fundamental frequency with different frequency components which are called harmonics.

The harmonic amplitude (HA) after amplification is fairly a fraction of the basic amplitude. It doesn’t cause any severe cause to the output waveform. If the HA after amplification goes to a high value, its effect cannot be avoided because it is visible at the output.

Here the input has fundamental frequency including harmonics. So the combination of the two on amplification provides a distorted signal at the output. It happens either because of the occurrence of reactive elements (or) through the amplifier circuit’s electrode capacitances.

Phase Distortion

Phase Distortion is also called delay distortion in the amplifier because whenever there is a time delay between the input & output signal then it is said to be phase distorted signal. This distortion mainly occurs because of electrical reactance. Earlier we have discussed that a signal includes different frequency components thus, whenever different frequencies experience different phase shifts then phase distortion occurs. This type of distortion has no practical importance in audio amplifiers because the human ear is insensible to phase shift. The type & quantity of distortion that is bearable or unbearable mainly depends on the amplifier’s application. Usually, the working of the system will get affected simply whenever the amplifier causes extreme distortion.

Reasons for Distortion

Distortion in amplifiers mainly occurs because of the main reasons which are discussed below.

• Distortion mainly occurs because of incorrect biasing whenever the input signal is not amplified for the complete cycle of the input signal.
• It occurs when the input signal applied is very large.
• Sometimes, amplifier distortion results whenever the amplification is not linear above the whole frequency range.
• Amplifier distortion can be caused by different factors; non-linearities within the components of the amplifier like transistors or tubes.
• In addition, impedance mismatches, power supply limitations & signal clipping can also contribute to amplifier distortion. So these factors result in the signal amplification that changes from the input signal and leads to an original signal distortion.
• Generally, harmonic distortion within amplifiers can be caused
• Harmonic distortion is a type of distortion in an amplifier that usually occurs by the amplifier which needs more voltage than the power supply it can provide.
• This can also occur with some internal circuit parts exceeding their output ability.
• Harmonic distortion occurs due to the nonlinearities of the transistors.
• This occurs mainly because of the active devices’ frequency-dependent characteristics.
• Amplitude distortion in amplifiers mainly occurs whenever the frequency waveform’s peak values are attenuated due to a shift within the Q-point.

How to Reduce Harmonic Distortion in Amplifiers

Harmonic distortion (HD) is one of the major issues that causes different problems like; crosstalk, signal integrity issues, and EMI (electromagnetic interference). It can be caused due to many reasons and there are different ways to decrease or remove harmonic distortion which is discussed below.

• Differential signaling is one of the methods used for reducing the harmonic distortion which can cancel out various harmonics.
• One more method is to use power supplies with low output impedance which can also assist in decreasing harmonics.
• Network reconfiguration is the procedure that helps in decreasing harmonics where the users generate large harmonics. These harmonics are identified & classified depending on the type of harmonics they produce.
• Adding multi-pulse converters for harmonics cancellation throughout the utilization of half and full-wave converters helps in eliminating harmonics.
• Phase balancing is one more technique that is suitable to reduce harmonics.
• Series reactors reduce harmonics in steel plants & smelting.
• Differential signaling is a method that is frequently used within high-speed digital systems for reducing the noise & crosstalk effects. The two signals in differential signaling are transmitted on separate wires with the single signal being the opposite of the other. After that, the receiving device merges the two signals & any common-mode noise can be canceled out.
• Power supplies through low output impedance can also assist in reducing harmonics.
• A low-impedance power supply has less voltage drop whenever current is drawn from so it can assist in decreasing or removing many of the issues that occur with harmonic distortion.

How to Measure Amplifier Distortion?

Amplifier distortion can be measured using analog spectrum analyzers. Most spectrum analyzers have 50ohm inputs, so an isolation resistor is required in between the DUT & the analyzer for simulating >50ohms DUT loads.

Once the spectrum analyzer is adjusted for sweep rate, sensitivity & bandwidth, verify it cautiously for overdrive of input. The simplest technique is to utilize the variable attenuator to set up 10dB of attenuation within the input path of the analyzer. Both the signal & any harmonics must be attenuated through a set amount as monitored on the display of the spectrum analyzer. If the harmonics are attenuated by >10dB, then the analyzer’s input amplifier is introducing distortion & the sensitivity must be decreased. Several analyzers have a button on top of the front plate to introduce a known quantity of attenuation while verifying for overdrive.

Difference b/w Amplifier Distortion Vs Distortion Pedals

The main differences between amplifier distortion and distortion pedals are discussed below.

Thus, this is an overview of amplifier distortion, working, and its applications. It refers to any variation from the input signal that occurs in the amplification process to provide an output signal. This signal is being altered in terms of frequency, shape, magnitude, etc. It occurs due to different factors like; non-linearities within the components of an amplifier, improper biasing, or amplifier overloading. There are different kinds of distortion available which have specific characteristics & causes. Generally amplifier distortion is undesirable because it can degrade the value of the amplified signal. Here is a question for you, what is an amplifier?