Frequency Downconverter, upconverter, multiplier, divider, mixer, or frequency translator? What is an RF Mixer?
Not to be confused with awkward socials at microwave industry events, RF Mixers are fundamental building blocks of many RF circuits and systems. The basic function of a RF mixer is frequency translation. Frequency translation shifts the frequency content of a signal, or set of signals, to another part of the spectrum. There are a variety of mixer types, some with specific applications and others that can be used in a variety of circuits as a basic mixer.
RF mixers are used in situations where the baseband or intermediate frequency (IF) is below that of the RF carrier frequency. A common reason for the use of a baseband or IF frequency is that the analog to digital converse (ADCs) and digital to analog converters (DACs) used to digitize and synthesize the signal may not have the bandwidth to directly digitize or synthesize the RF, and one or more intermediate frequency stages are needed to translate the signal to a useable frequency.
RF Mixer with SMA Connectors
Basic mixers are three terminal RF devices. One port is typically designated as the RF port, which is the higher frequency port. Another is the IF port, which is the lower frequency port. The last port is the local oscillator (LO) port. It is important to remember that RF Mixers of every sort are intrinsically nonlinear devices. Hence, they don’t just produce the desired RF or IF output, but also produce harmonics that are a function of the two inputs, and other nonlinearities, such as spurs. To help with this, RF Mixers are often followed by a band-pass, low-pass, high-pass filter, depending on the requirements of the circuit.
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Peter McNeil | Sep 28, 2022 | RF Mixers
RF mixers are frequency conversion devices that are composed of nonlinear elements that allow for frequency “mixing” of RF, intermediate frequency (IF), and local oscillator (LO) signals. There are two main functions of RF mixers: either upconversion or downconversion. Upconversion is the process of combining two input signals, the IF and LO, to generate multiple combinations (the sum, difference, and harmonics) of the two input signals that are the RF signals. Downconversion is the reverse process of upconversion, where the two input signals, RF and LO, are combined to yield the IF signals.
Double Balanced RF Mixer