Gain (electronics)
Gain measures a circuit's ability to amplify a signal.
Gain, in electronics, is a measure of the ability of a two-port circuit, often an amplifier, to increase the power or amplitude of a signal from the input to the output port by adding energy converted from a power supply. It is usually defined as the mean ratio of the signal amplitude or power at the output port to that at the input port, and is often expressed using the logarithmic decibel (dB) units. Gain greater than one (greater than zero dB) is the defining property of an active device or circuit, while a passive circuit has a gain of less than one.
- Definition
- Ratio of output to input signal amplitude or power
- Common units
- Decibels (dB) or nepers (Np)
- Types
- Voltage gain, current gain, power gain
- Context variation
- Audio amplifiers usually refer to voltage gain; radio frequency amplifiers usually refer to power gain
- Frequency dependence
- Gain generally varies with frequency; unless stated, refers to passband gain
- Antenna gain
- Ratio of radiation intensity from a directional antenna to mean radiation intensity from a lossless antenna
Lore & Background
The term gain alone is ambiguous, as it can refer to the ratio of output to input voltage (voltage gain), current (current gain), or electric power (power gain). In audio and general-purpose amplifiers, especially operational amplifiers, the term usually refers to voltage gain, but in radio frequency amplifiers it usually refers to power gain. The term gain is also applied in systems such as sensors where input and output have different units; in such cases the gain units must be specified, as in '5 microvolts per photon' for the responsivity of a photosensor.
Reader's Guide
Gain is a fundamental concept in electronics, defining the amplification capability of circuits. Its significance lies in enabling signal processing, communication, and sensing technologies. The use of logarithmic decibel units allows convenient expression of large ratios and facilitates calculations involving cascaded stages. The distinction between voltage, current, and power gain is crucial for proper circuit design and analysis, as is the recognition that gain varies with frequency. The simplified 20 log rule for voltage gain in decibels applies only when input and output impedances are equal. Understanding gain is essential for designing amplifiers, filters, and other signal-processing systems, and its definition extends to antennas and sensors, where input and output units may differ.
Did You Know?
- Gain greater than one (greater than zero dB) is the defining property of an active device or circuit.
- The gain of a bipolar transistor normally refers to forward current transfer ratio, either hFE (beta) or hfe (small-signal current gain).
- Power gain in decibels is defined as 10 log10(Pout/Pin).
- When input and output impedances are equal, voltage gain in dB simplifies to 20 log10(Vout/Vin).
More in Electromagnetism And Waves 1-23
Spotted an error? Know more?
This is a living reference — every entry is fact-audited, and reader corrections feed straight into our audit queue. Suggest an edit · See this site's audit record