Frequency generator

摘要

To generate finely adjustable frequencies within a wide frequency range, frequency generators are known which contain a number of phase-locked loops, the output signals of which are mixed in mixing stages. During these mixing operations, noise signals are produced, the suppression of which requires high circuit complexity. A first phase-locked loop (PLL1) is provided which enables the output frequency (FA) to be adjusted in coarse steps. The first phase-locked loop (PLL1) is preceded by two further phase-locked loops (PLL2, PLL3) by means of which the frequency steps of the first phase-locked loop (PLL1) can be interpolated. The requirements for the phase-locked loop (PLL3) with respect to spectral purity are not high. Frequency generator in digital measuring instruments. <IMAGE>