The first factor is the frequency band. The frequency band corresponds to the operating speed of the amplifier. At high frequencies, the amplifier cannot keep up with the input signal and the amplitude of signal decreases.
The figure shows the frequency until the amplitude reaches -3 dB in the frequency band. Therefore, it is necessary to select an amplifier with a frequency band with a margin for the frequency you want to use. The rise time and fall time are related to the frequency band. The second factor is a slew rate that represents the response speed of the amplifier. This shows the maximum voltage rise rate of the amplifier. Generally, it is expressed by the amount of voltage change per micro second.
The response speed of the amplifier may be limited by the frequency band or by this slew rate. When the step response is limited by the slew rate, the rising waveform becomes straight as shown in the figure. So far, it was due to speed, but now we will introduce things related to load.
The first factor is inductive load. For example, when trying to output a square wave with a fast rise speed, the desired waveform may not be obtained because the voltage is limited by the overvoltage protection. In such case, it is necessary to slow the rising speed of the input signal and select a model that supports the generated voltage. In addition, using a step-like signal such as digital control for the input signal will generate many voltage pulses as well.
As these pulses may create a problem, it is recommended to use continuous waveform input signal as much as possible. On the other hand, overvoltage protection also limits the output signal. However, if the output signal is suddenly turned off, the protection does not work and a large voltage may be generated from the inductive load. The second factor is capacity load. Contrary to inductive load, large current is required when trying to operate at high speed under constant-voltage CV control.
When handling a large capacity, understand the load characteristics and the output characteristics of the power supply before use. The third factor is a diode load. Under constant-current CC control, even if the current control is zero under no load condition, the output voltage rises to the positive or negative overvoltage protection level under the influence of a slight offset.
This means that a diode or other load that only allows forward current can output signal an excessive voltage in the reverse direction even when the current control is zero. If this exceeds the withstand voltage of the load, it may cause a failure, so it is necessary to take measures such as inserting a protective diode in the reverse direction.
Last factor is the cable. When operating the amplifier at high speed, we cannot ignore the effects of the capacitance and inductance of the cable for output signal.
In high-voltage amplifiers, the cable has a capacitance between the output wire and the shield, so the capacitance affects the rising speed of the voltage waveform. Wideband amplifiers must have a constant gain from DC to several tens of MHz. They are used in measuring equipment such as oscilloscopes etc. Because of their extremely wide bandwidth, gain is low. DC amplifiers are used to amplify DC 0Hz voltages or very low frequency signals where the DC level of the signal is important.
They are common in many electrical control systems and measuring instruments. Video amplifiers are a special type of wide band amplifier that also preserve the DC level of the signal and are used specifically for signals that are to be applied to CRTs or other video equipment. The video signal carries all the picture information in TV, video and radar systems. The bandwidth of video amplifiers depends on use.
Buffer amplifiers are a commonly encountered, specialised amplifier type that can be found within any of the above categories, they are placed between two other circuits to prevent the operation of one circuit affecting the operation of the other. Often buffer amplifiers have a gain of one, i. This ensures that signals are not attenuated between circuits, as happens when a circuit with a high output impedance feeds a signal directly to another circuit having a low input impedance. Today they are widely used in integrated circuit form where they are available in single or multiple amplifier packages and often incorporated into complex integrated circuits for specific applications.
The design is based on a differential amplifier, which has two inputs instead of one, and produces an output that is proportional to the difference between the two inputs. Without negative feedback, op amps have an extremely high gain, typically in the hundreds of thousands.
Amplifiers are used to increase the amplitude of a voltage or current, or to increase the amount of power available usually from an AC signal. Whatever the task, there are three categories of amplifier that relate to the properties of their output;.
In a power amplifier, the product of voltage and current i. Note that either voltage or current may be less at the output than at the input. It is the product of the two that is significantly increased. Hons All rights reserved. Revision This additional power is supplied by a D. C voltage which is externally provided. The output signal is controlled by the input signal in an amplifier.
In Electronic components, which are compact, small-signal amplifiers are commonly used devices as they have the capability to raise a relatively small input signal to a larger magnitude.
For example from a Sensor such as a photo device, into a much larger output signal to drive a relay, lamp or loudspeaker. Therefore the op-amp equation can be given by.
We can now specify the characteristics for a perfect amplifier from our discussion above with regards to its Gain, meaning voltage gain:. Getting ideal machinery or circuit is impossible. Data and charts, if used, in the article have been sourced from available information and have not been authenticated by any statutory authority. The author and Marine Insight do not claim it to be accurate nor accept any responsibility for the same.
The views constitute only the opinions and do not constitute any guidelines or recommendation on any course of action to be followed by the reader.
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