Frequency mixer

A nonlinear circuit that combines two signals to produce new frequencies, typically their sum and difference. It enables frequency conversion in radio transmitters and receivers.

Heterodyning: The process of combining signals to generate new frequencies from their sums and differences. It names the frequency-conversion process performed by a mixer.
Fourier analysis: A mathematical method for representing signals as sums of sinusoidal components. It describes the new spectral components produced by mixing.
Superheterodyne receiver: A radio receiver that converts incoming signals to an intermediate frequency before detection. Its defining frequency-conversion stage is a mixer.
Diode ring mixer: A balanced mixer built from a ring of diodes and transformers. It is a common passive design with strong isolation and odd-order mixing products.
Nonlinear system: A system whose output is not proportional to its input and whose responses can generate new frequencies. A mixer's nonlinearity allows input frequencies to interact.
Frequency spectrum: The distribution of a signal's amplitude or power across frequencies. Mixer behavior is understood by tracking input and output spectral components.
Direct-conversion receiver: A receiver that converts a radio signal directly to baseband using a local oscillator near its carrier. Its mixer translates the desired channel without a fixed intermediate frequency.
Gilbert cell: A transistor circuit that implements a differential analog multiplier. It is a common active mixer architecture that can provide conversion gain.
Intermodulation: The production of additional frequency components when signals pass through a nonlinear system. It explains both useful mixing products and unwanted spurious tones.
Gain compression: A reduction in a circuit's gain as its signal level approaches nonlinear operating limits. Excessive drive can distort mixer outputs and reduce conversion performance.

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