Abstract :
Recently, Langham proposed an original technique for frequency multiplication. His circuit uses two oscillators and a simple digital processor. One of the oscillators serves for measuring the period of the input waveform, the other determines the period of the output waveform. The multiplication factor of this frequency multiplier is equal to the ratio of the frequencies of the two oscillators. This circuit has certain advantages when compared to conventional frequency multipliers: it is capable of multiplying the input frequency by any positive real rational number, and yet it is an open-loop system, inherently stable and capable of tracking even the fastest changes in input frequency. One of its main drawbacks is the direct dependence of the accuracy and stability of its multiplication factor on the tracking characteristics of two independent oscillators. A way of eliminating this drawback is proposed here. It involves discarding one of the reference oscillators at the cost of adding a readonly memory (ROM). The modified system is insensitive to reference frequency variations and its accuracy is determined only by the roundoff errors in the digital processor.
