| 摘要 |
<p>An ultrasonic Doppler ground speedometer comprises an ultrasonic transmitter (2) for transmitting an ultrasonic wave signal at a predetermined angle onto a road surface (4); an ultrasonic receiver (5) for receiving an ultrasonic wave signal reflected from the road surface; a reference signal generator (7) for generating a reference signal with a constant frequency (fREF); a phase locked loop (PLL) circuit (17) composed of a phase comparator (8) for generating a difference voltage signal according to difference (fREF-fR) in frequency (or phase) between the reflected signal and the reference signal, a voltage controlled oscillator (11) for generating the transmitted signal so as to keep the reflected signal frequency (fR) at the reference signal frequency (fREF); and arithmetic circuit (12, 13, 14) for calculating ground speed (v) from Doppler shift (fD) between the transmitted signal frequency (fT) and the reference signal frequency (fR). The above reference signal generator, the PLL circuit, and other additional circuits can be all configured by separate IC chips now put on the market, thus realizing an ultrasonic speedometer small in size and low in cost.</p> |
