Implementing Modulation Functions in Microwave Frequency Synthesizers

The main function of a frequency synthesizer is to deliver a stable and clean signal. However, many applications require not only a fixed frequency signal but also various modulation functions ranging from simple pulse, amplitude, frequency and phase modulation to complex digital modulation formats. Although modulators are usually realized as external devices, they can also be incorporated into a frequency synthesizer core. Inside any synthesizer there are many circuits that can carry multiple functions and be reused to increase the functionality without a significant increase in cost. This results in a more cost efficient and versatile design. The most commonly used modulation schemes are briefly reviewed in this article. Further details on modulation theory and implementation techniques can be found in [1-7].