| 摘要 |
A vehicle carries a radar transmitter (12) and receiver (14) which provides a Doppler signal representing vehicle ground speed. The Doppler signal is processed by a Schmitt trigger (18) and a flip-flop (20) to generate a symmetrical square wave whose instantaneous pulse-width is the reciprocal of the Doppler frequency. A microprocessor is interrupted by edges of the square wave and processes the pulse-width to produce a symmetrical output square wave (23). The processing steps comprise:… (1) Input pulse widths exceeding a threshold value set by a timer are ignored… (2) When the input pulse width INVAL is within 121_2% of the output pulse width OUTVAL the latter is updated in accordance with a weighted average, OUTVAL = (15 OUTVAL + INVAL)/16… (3) When the input pulse width INVAL deviates more than 121_2% from the output pulse width OUTVAL no updating occurs unless this situation has persisted for 8 or more input pulses, whereupon more abrupt updating occurs in accordance with a second weighted average… OUTVAL = (3 OUTVAL + INVAL)/4… where INVAL is the average INVAL over 8 input pulses when the second weighted average is first used but is the latest input width when the situation has persisted for more than 8 input pulses. |
