An RF (radio frequency) mixer is an electronic device that is used to combine two or more input signals to produce a new output signal at a different frequency. This process is known as frequency mixing or heterodyning. RF mixers are used in a wide range of applications, including radio and television transmission, radar, and communications systems. They are also used in some types of electronic test equipment, such as vector network analyzers.
There are several different types of RF mixers that can be used to achieve different performance characteristics. Some of the most common types include diode mixers, transistor mixers, Gilbert cell mixers, image reject mixers, direct conversion mixers, hybrid mixers, and digital mixers.
Diode Mixers
Diode mixers are one of the most common types of RF mixers. They use one or more diodes to non-linearly mix the input signals, typically a local oscillator (LO) and RF signal. The diode is used to rectify the input signals, which produces a difference frequency at the output. The LO signal is used to shift the RF signal to a new frequency, which is known as the intermediate frequency (IF).
One of the main advantages of diode mixers is that they are relatively simple and inexpensive to build. However, they also have some disadvantages, such as poor isolation between the input and output ports, which can lead to unwanted signals at the output.
Transistor Mixers
Transistor mixers are another type of RF mixer that uses transistors to non-linearly mix the input signals. Like diode mixers, they produce a difference frequency at the output by rectifying the input signals. However, transistor mixers have some advantages over diode mixers, such as better isolation between the input and output ports and the ability to handle higher input power levels.
A transistor mixer can be a BJT mixer or FET mixer which can be either JFET mixer or MOSFET mixer respectively. Also the transistor mixer may use multiple transistor like in diode mixer. Example includes two JFET based mixer. Furthermore within the transistor mixer, different topology is used such as collector modulator or emitter modulator.
Gilbert Cell Mixers
Gilbert cell mixers are a type of RF mixer that uses a special type of active device called a Gilbert cell, which is a type of differential amplifier that can be used to mix signals. Gilbert cell mixers have some advantages over diode and transistor mixers, such as better linearity, lower distortion, and the ability to handle high input power levels.
An example of mixer where Gilbert cell mixer is used is the MC1496 modulator/demodulator IC. Within the IC(Integrated Circuit), a differential amplifier modulator with current source transistor are employed to make the mixer.
Image Reject Mixers
Image reject mixers are a type of RF mixer that uses two or more diodes to produce a difference frequency. The advantage of this type of mixer is that it eliminates the image frequency problem, which is a common problem in RF mixers. The image frequency is an unwanted frequency that is produced at the output of the mixer when the LO frequency is close to the RF frequency.
Direct Conversion Mixers
Direct conversion mixers are a type of RF mixer that directly convert the input signal to the desired frequency by using a balanced mixer. This type of mixer is mostly used in receiver front ends. Direct conversion mixers have the advantage of having a simple structure and low noise figure. However, they are also sensitive to LO leakage.
Hybrid Mixers
Hybrid mixers are a type of RF mixer that use a combination of passive and active components to mix the signals. They typically use a combination of diodes and transistors. Hybrid mixers have some advantages over diode and transistor mixers, such as better isolation between the input and output ports, lower distortion, and the ability to handle high input power levels.
Digital Mixers
Digital mixers are a type of RF mixer that use digital signal processing techniques to perform the mixing function. They are mostly used in digital receiver front ends. Digital mixers have the advantage of having a wide dynamic range, high accuracy, and easy
