Signal Conversion
Frequency conversion occurs when two electrical signals are combined in a non-linear device to produce new frequencies. This rf mixing generates the sum and difference of the input signals, allowing high-frequency data to be shifted to a lower range for processing. It is a fundamental operation in radio receivers and transmitters.
Heterodyne Technique
Signal processing uses this technique to translate a radio wave to an intermediate frequency. In rf mixing, a local oscillator provides a stable reference that beats against the incoming signal. This allows the receiver to use fixed filters for tuning and amplification.
Distortion Product
Unwanted products are a side effect of the non-linear process. The rf mixing produces harmonics and intermodulation products that can interfere with the desired signal. Designers specify the third-order intercept point to define the dynamic range of the mixer.
Bandpass Filter
Filtering is required to remove the original frequencies and the unwanted sum products. The rf mixing stage is followed by a bandpass filter that only allows the target frequency to pass. This ensures that the subsequent stages of the receiver are not overloaded by out-of-band energy.
Because the mixer is sensitive to impedance, matching networks are placed at the input and output ports.
