Gain (electronics)

Some tools make signals bigger.

They take a small signal.

Then they add energy from a power source.

Now the signal is much stronger.

This is called gain.

Gain tells us how much bigger it gets.

If the signal stays the same size, it is called unity gain.

Some tools can also make a signal smaller.

This happens in a passive circuit.

It is fun to see how things grow!

In electronics, gain is a way to measure a signal.

It tells us how much a signal grows. An amplifier takes a small signal at the input. Then it adds power from a power supply. This makes the signal larger at the output.

There are different types of gain. Voltage gain looks at the change in voltage. Current gain looks at the change in current. Power gain looks at the change in electric power. Most audio tools use voltage gain. Radio tools often use power gain.

We can measure gain in many ways. One way is to use a ratio. This means we divide the output by the input. We can also use decibels, or dB. Decibels are a way to show a scale.

If the gain is exactly one, we call it unity gain. This means the input and output are the same. An active device has a gain greater than one. A passive circuit has a gain less than one. The gain can change based on the signal frequency. This is the speed of the signal.

A graph showing how an input signal becomes a larger output signal.

In electronics, gain is a special way to measure a signal. It tells us how much a circuit can increase a signal. This often happens in a tool called an amplifier. An amplifier takes a small signal at its input port. Then, it adds energy from a power supply to that signal. This extra energy makes the signal larger at the output port.

This process is why we call these active devices. A passive circuit is different because its gain is less than one. This means the signal does not grow larger.

There are a few ways to look at how gain works. One way is to look at voltage gain. This measures the ratio of output voltage to input voltage. Another way is current gain. This looks at the ratio of output current to input current. Some people also measure power gain. This looks at the ratio of electric power at the output to the input.

In audio tools, people usually talk about voltage gain. In radio frequency tools, they usually talk about power gain. Even sensors use gain to show how they change inputs into outputs.

Scientists use different math to describe these numbers. One common way is to use a ratio. You can find this by dividing the output by the input. Another way is to use decibels, which are called dB. Decibels are a logarithmic way to show the relationship.

You can also use nepers, which use a natural logarithm. If the input and output are exactly the same, we call it unity gain. This is a gain of factor one. In decibels, unity gain is equal to zero dB.

Specific parts like transistors have their own rules for gain. For a bipolar transistor, gain often means the current transfer ratio. This is sometimes called hFE or beta. It is the ratio of the output current to the input current.

This is measured in amperes. The gain of a device can also change with frequency. Frequency is how fast the signal moves. Most people talk about the gain within a specific range called the passband. This is the range the equipment is meant to use.

Think about a small whisper becoming a loud shout. That is a lot like how gain works in a circuit.

If you have an amplifier with a 50 ohm input, it can change things. For example, a 1 volt input might become 10 volts at the output. This would give you a voltage gain of 10. You can also calculate the power gain using this same information. It is all about how much the signal grows from start to finish.

In electronics, gain is a measure of how much a signal grows. It describes a two-port circuit's ability to increase signal amplitude or power. This process usually happens within an amplifier. An amplifier takes a signal at its input port and increases it at the output port. To do this, it must add energy. This energy is converted from an external power supply into the signal.

This ability to increase a signal is what makes a circuit an active device. In contrast, a passive circuit will always have a gain of less than one.

Gain can be measured in several different ways depending on the signal type. The term is often ambiguous because it can refer to different properties. Voltage gain is the ratio of the output voltage to the input voltage. Current gain is the ratio of the output current to the input current. Power gain is the ratio of the output electric power to the input power.

In the world of audio and general purpose amplifiers, people usually mean voltage gain. However, in radio frequency amplifiers, the term usually refers to power gain. In some systems like sensors, the input and output might use different units entirely.

Mathematical units help engineers describe these ratios clearly. One common method is using a logarithmic scale called decibels, or dB. This is often called "dB gain." Another way to calculate these relationships is by using nepers. Nepers are calculated using a natural logarithm instead of a decimal logarithm.

When the input and output levels are exactly the same, it is called unity gain. Unity gain is a gain factor of one. In logarithmic terms, unity gain is equal to zero dB. This means the signal has not been increased or decreased.

To calculate power gain in decibels, you use the ratio of output power to input power. Specifically, you take the logarithm of the output power divided by the input power. If you want to calculate voltage gain using decibels, you can use the 20 log rule. This rule works if the input impedance and output impedance are equal. Impedance is a measure of resistance in an AC circuit.

A similar calculation exists for current gain. When calculating current gain in decibels, you use the ratio of output current to input current. Like the voltage rule, the 20 log rule for current gain assumes equal impedances.

Specific electronic components like the bipolar transistor have unique ways of defining gain. For these devices, gain usually refers to the forward current transfer ratio. This is sometimes called hFE or "beta." It is the static ratio of the output current (Ic) to the input current (Ib).

Another measure is hfe, which is the small-signal current gain. This is the slope of a graph showing Ic against Ib at a specific point. These values are dimensionless because they are ratios of the same unit, such as amperes. However, other devices like the operational transconductance amplifier use SI units like siemens. This happens because their gain is a ratio of output current to input voltage.

It is important to remember that gain is not always a fixed number. The gain of an electronic device or circuit generally varies with the frequency of the signal. Frequency refers to how many times a signal repeats in a second. When engineers discuss gain, they usually refer to the gain within the passband. The passband is the intended operating frequency range for that specific piece of equipment.

If a signal falls outside this range, the gain might change significantly.

We can see how these numbers work with a practical example. Imagine an amplifier has an input impedance of 50 ohms and a load of 50 ohms. If the input voltage is 1 volt and the output voltage is 10 volts, the voltage gain is 10. To find the power gain, you use the formula for power, which is voltage squared divided by resistance. In this specific case, the power gain would be 100.

This shows how a small change in voltage can lead to a much larger change in power.

Gain is a fundamental concept that connects to many different areas of science and engineering. In antenna design, the term takes on a different meaning. Antenna gain is the ratio of radiation intensity from a directional antenna to the mean radiation intensity from a lossless antenna. This helps engineers understand how well an antenna directs its signal. Whether in radio, audio, or sensors, understanding gain is essential for controlling how energy moves through a system.