Amplifier measurements include the evaluation of the characteristics of the amplifier. when the amplifier is being powered with an input signal that excites it to its nominal output level, the output impedance should be measured. Amplitude linearity can be determined by measuring output power vs. input power
The degree of amplification supplied by an amplifier is measured by its gain, which is the ratio of output voltage, current, or power to input voltage, current, or power. An amplifier is a circuit with a power gain greater than one.
What Unit of Measurement Is an Amplifier
You can use an amplifier to measure various things. Such as gain, frequency, bandwidth, voltage, current, and impedance. Hence, the units will also vary along with the measurement that you’ll be going for.
For example, if you’re measuring gain, the unit will be decibels (dB). If you’re measuring frequency, voltage, current, or impedance the units will be Hertz(Hz), Volts(V), Amperes(A), and Ohms respectively.
What Parameters Do Amplifier Measurements Involve
Certain parameters are believed to exist in any amplifier measurements. These are the specific qualities that cause the amplifier to behave in a certain way and hence make it suitable for a given task. The following sections explain typical amplifier parameters.
- Gain
The gain of an amplifier is a measurement of the “Amplification” of the amplifier, or how much it amplifies the amplitude of a signal. The symbol “A” represents the ratio of the output signal amplitude to the input signal amplitude. It is possible to compute it for voltage (Av), current (Ai), or power (Ap).
Voltage gain Av = Amplitude of output voltage ÷ Amplitude of input voltage.
Current gain Ai = Amplitude of output current ÷ Amplitude of input current.
Power gain Ap = Signal power out ÷ Signal power in.
- Frequency Response
At all frequencies, amplifiers do not have the same gain. An amplifier built for audio frequency amplification will amplify signals with frequencies less than roughly 20kHz but will not amplify signals with higher frequencies.
A radio frequency amplifier will enhance a band of frequencies above roughly 100kHz but will not amplify lower-frequency audio signals.
Figure 1: Frequency Response of an Amplifier
- Bandwidth
The Bandwidth of the amplifier is an important piece of information that can be acquired from a frequency response curve. This refers to the frequency ‘band’ for which the amplifier has a useful gain.
Outside of this useable range, the amplifier’s gain is deemed insufficient in comparison to the gain at the center of the bandwidth. The bandwidth specified for voltage amplifiers is the frequency range for which the amplifier’s gain is greater than 0.707 of its maximum gain.
- Input and Output Impedance
An amplifier’s input impedance is the effective impedance between its input terminals. The term “effective” denotes that the impedance is not necessarily limited to the impedance of the amplifier components (resistors, capacitors, etc.) physically connected across the input terminals.
The output impedance of an amplifier is not primarily determined by the components connected within the amplifier’s output. It is an ‘apparent’ impedance and is best demonstrated as being responsible for a drop in signal voltage at an amplifier’s output terminals when a current is pulled from the output terminals.
Figure 2: Input and Output Impedances
- Phase Shift
The amount (if any) by which the output signal is delayed or advanced in phase with respect to the input signal in an amplifier is stated in degrees. If there is a 90-degree phase shift, the peak of the output wave comes one-quarter of a cycle after the peak of the input wave.
Frequently Asked Questions and Answers (FAQs)
What Is the Use of Measuring Amplifier?
Measuring amplifiers are used in universal signal processing to transform strain gauge data from strain, force, and load cells equipped with strain gauge full bridges to an output level. They are a critical link in the measurement chain since the quality of subsequent signal processing is largely dependent on their accuracy.
What Is the Best Amplifier Frequency Response?
2 or 3dB is considered extremely good for speakers, headphones, and microphones. Amplifiers, CD/DVD players, and other strictly electronic’ devices should be no more than 0.5 or 1dB apart.
Conclusion
A signal amplifier’s gain can range from 5 to 25 dB or more. The output may be compressed by 1 dB anywhere between -10 and +20 dBm. These are common ranges. However, amplifiers with 1 dB compression over +20 dBm enter the PA area.
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