Frequency multipliers are devices that multiply the frequency of an input signal by a desired number. Frequency multipliers are typically used in radio frequency (“RF”) and microwave test instruments and communications systems to extend the frequency range of lower frequency sources. The multiplied signals may be generated using non-linear devices, which may include either passive (such as Schottky diodes) or active (such as Field Effect Transistors or Bipolar Junction Transistors) devices. Diodes generally operate at higher frequencies than transistors and are the preferred choice for the highest frequency multipliers. However, diodes typically require higher power to operate and have higher conversion loss. Transistors, on the other hand, are convenient to use since they have a gain and can generate multiplied frequencies at lower power levels.
Frequency multipliers include non-linear elements for generating frequency harmonics of the input signal. The generated harmonics of the input signal are output as the desired multiplied signals. The critical frequency of the input signal is typically suppressed in the multiplier so that the output signal has primarily harmonic frequencies. A multiplier is usually designed to suppress the critical frequency and enhance either the even harmonics (2fo, 4fo, 6fo, etc.) or the odd harmonics (3fo, 5fo, 7fo, etc.). Such frequency multipliers are called even harmonic multipliers and odd harmonic multipliers, respectively, or more commonly, frequency doublers and frequency triplers, respectively.
A significant disadvantage of existing frequency multipliers is that they perform a single function by operating over a specific multiplication frequency band. It is common in communications systems and test instruments to need signals at either the critical frequency or at multiplied frequencies depending on the state of the system. The specific multiplication frequency band may not provide a sufficient range of frequencies. Existing frequency multipliers are single multiplication frequency band devices that are connected with switching networks to select signals at different multiplied frequency bands or at the critical frequency.
In view of the foregoing, there is an ongoing need for frequency multipliers capable of generating multiplied frequencies in different multiplication frequency bands.