Tips on Selecting a Frequency Divider or Frequency Multiplier
Frequency translation is the backbone of superheterodyne communications and radar circuits, as well as many other useful RF/microwave devices. There is often confusion surrounding these nonlinear devices, specifically the role of mixers, multipliers, and dividers, and how to select the best device for an application. This post aims to briefly describe the similarities and differences, and some illumination on device selection criteria.
What is a Mixer?
A mixer is a nonlinear, three-terminal device, often comprised of a diode or transistor operating in the nonlinear region. From two input signals, a mixer will produce the sum and difference of the two signals in the output. This can be used in upconversion, downconversion, as an IQ mixer, or with different performance parameters based on configuration. Mixers are commonly used in demodulation circuitry, upconverters, and downconverters, providing frequency translation before transmission, or after reception.
What is a Multiplier?
A multiplier is a nonlinear device, which generates harmonics of higher frequencies based on an input signal’s behavior. For example, a doubler is a frequency multiplier that creates a strong 2nd harmonic. Inevitably, the input signal, higher harmonics, and noise/interference will also leak and be mixed in with the output signal. Multipliers are often used in demodulation circuitry and to raise the frequency of an oscillator or signal generator source.
What is a Divider?
A frequency divider is similar to a frequency multiplier, with the exception that the output frequencies are a submultiple of the input signal frequencies. The same considerations apply to dividers, as they do to multipliers.
What should I know when choosing Multipliers or Dividers?
As part of the many use cases of multipliers and dividers, isolation, harmonic suppression, and phase noise characteristics are important factors to consider when selecting a multiplier or divider. Isolation describes how well the signals input into the multiplier or divider are prevented from leaking into the output, while harmonic suppression describes how well the multiplier or divider design prevents harmonics of the input signal from appearing at the output. Both factors are critical, as they directly impact the usability of a multiplier or divider device. Additive phase noise and noise performance of a multiplier or divider are important for signal generation and modulation circuitry that is noise, phase noise, or interference limited, as these parameters describe with the device adds to an input signal when generating the output signal.
The amount of signal power needed to drive the multiplier or divider, or necessary signal input power for proper operation, may also be a factor to consider, as some multipliers and dividers require substantial input powers. Many test and measurement grade precision signal generators, and arbitrary waveform generators, may not produce the necessary signal strength to drive a multiplier or divider. Hence, an amplifier, which as its own distortion, noise, and phase noise, may be required.