An up-down converter and mixer is a device that is intended to convert an analog signal between a lower frequency and a higher frequency. When converting to a higher frequency, the device is said to up-convert, and when it converts a high frequency to a lower one it is said to down-convert. They are typically used in receiver front-ends or in the transmitter signal path to generate the RF signal for subsequent amplification.

These devices usually have a low noise amplifier to modify the strength of a received signal. Low noise is important because any noise generated by the amplifier itself will add to the noise already present on the received signal and will be amplified by the device, thus increasing the noise figure. The amplifier may have adjustable gain. The signal then passes into a mixer element, usually an active component in a double balanced topology. The mixer mixes the incoming RF signal in the time domain with a reference frequency from the local  oscillator (LO).  As a result two frequency products (the difference and sum) are produced. Because of the double balanced topology, the sum product is suppressed, and the difference product is the output. This difference product is either at a lower frequency called an intermediate frequency (IF) for additional down-conversion or it is converted down to the origin (base-band, or zero Hz).  The output is typically differential and passes into a matching network in the case of an IF where it is then filtered with a device like a ceramic or crystal band pass filter before passing onto to the demodulator.

In the case of the transmitter path, the IF or a base-band modulated signal is input to a mixer that is multiplied by an LO to produce the RF signal. The RF signal is then filtered by an external band-pass filter (for example, a SAW filter) to eliminate spurious frequency products, before being passed into a power amplifier driver with adjustable gain. This PA Driver may be integrated into the device. The RF signal passes to another external band-pass filter before being sent to the power amplifier for transmission.

An important specification for these devices is the third order intercept point (IP3). IP3 is a measure of the third order term of the polynomial series that describes the non-linear characteristics of the device. It is the input power level where the coefficients of the first and third order terms have equal amplitudes. This is related to an amplifiers 1dB compression point, where the nice sinusoidal-like signal starts to become a square signal. These devices are used in Cellular transceiver applications, ISM Band Receivers, and other communication applications.