According to the principle of direct digital synthesis, a continuous frequency modulation signal generator is designed based on MSP 430F135 microcontroller as main control circuit and amplitude adjustment circuit, direct digital synthesis circuit, signal amplification circuit, display and keyboard circuit. To address the shortcoming of large computation, low efficiency of frequency setting, more storage space occupied or significant cumulative errors of frequency setting when calculating frequency control word with traditional methods, a novel calculation way for frequency control word is researched. This new method does not need large computation and more space and simultaneously it can decrease the error greatly. Taking reference clock frequency of 2MHz, phase accumulator bit of 28, frequency resolution of 0. 1, the maximum output frequency of 1MHz as an example, when the output frequency is 1kHz, the absolute error is 31Hz using common method and the maximum absolute error is 0. 026Hz using new algorithm. So, the signal generator with this new method adopted has characteristics of wide frequency range set. Adjustable frequency and fast response and can be well applied in calibrating turbine flown meter.%根据直接数字合成技术( DDS)的原理,以微控制器MSP430F135为主控电路,由幅值调整电路、直接数字合成、信号放大、显示及键盘电路等组成,设计了一种频率连续可调的信号发生器；针对传统计算频率控制字存在的计算量大、频率设定效率低、占用存储空间大或设定频率有误差累积效应等缺点,研制了一种新的计算频率控制的算法,该方法不需计算大量数据和大量存储空间且可显著减低误差的累积效应；以参考时钟频率为2MHz,相位累加器位数为28,步距为0.1,最大输出频率为1MHz为例,输出频率为1kHz时,采用传统算法计算其绝对误差达31Hz,而采用新算法最大的输出频率绝对误差为0.026Hz；因此利用该算法设计的信号发生器,具有频率范围设定宽、频率连续可调、响应速度快等特点,可较好地应用在涡轮流量计的出厂校验中.
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