| 摘要 |
<p>As shown in Figure 1, a pulse generator comprises a digital oscillator (1) which produces a succession of numbers from which a periodic analogue waveform is produced. These numbers can represent a triangular waveform (TW) (or a sine waveform). Their direct conversion into analogue form by a digital-to-analogue converter (3), followed by integration by an integrator (4), would result in the production of a distorted analogue waveform (SW) which when limited by a limiter (5) would produce an output pulse waveform (OPW) with an inaccurate mark/space ratio. The invention provides a subtraction circuit (2) which subtracts each number produced by the digital pulse generator (1) from the previous number, to produce a series of new numbers (MW) which represent a pre-distorted waveform. When these new numbers are converted into analogue form, the integration of the resulting waveform (MW') by the integrator (4) produces an analogue waveform (SW) with clearly defined zero crossings. The output pulse waveform (OPW) is thereby given a reliable mark/space ratio. Furthermore, when the pulse generator is driven by a clock whose frequency is several times greater than the frequency of the output pulse waveform (OPW), the latter suffers only small phase modulation (jitter).</p> |
