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本文介绍的电压频率变换器采用常见的锯齿波方法,而积分电容放电时间引起的误差,通过在电压电流变换级加入一对数修正系数来减少。按照图1所示方块图,可得出如下关系。对数修正: 只有当电容放电时间可忽略时,f和V_E间的比例关系才能得到保证。按所用晶体管,100微微法电容充电到2伏,其放电时间t_r为几毫微秒。然而,在20兆赫频率(r=50毫微秒)时,该时间约为周期的10％,因而不可忽略。实际的频率由下式给出:
The voltage-to-frequency converter introduced in this paper uses a common sawtooth method, and the error caused by the discharge time of the integrating capacitor is reduced by adding a logarithmic correction factor at the voltage-current conversion stage. Following the block diagram shown in Figure 1, the following relationship can be drawn. Logarithmic correction: only when the capacitor discharge time is negligible, the relationship between f and V_E can be guaranteed. According to the transistor used, a 100 picofarad capacitor is charged to 2 volts, and its discharge time t_r is a few nanoseconds. However, at 20 megahertz (r = 50 nanoseconds), this time is about 10% of the period and therefore can not be ignored. The actual frequency is given by: