| 摘要 |
An automatic tuning circuit for an RC filter is provided to reduce the time for tuning by finding the cut-off frequency of the main RC filter with the direct method not the sequential method and to output control signal for adjusting resistance values of a slave RC filter and a main RC filter. An automatic tuning circuit for an RC filter includes a comparer, a time-to-digital converting unit(140), and a decoder. The comparator compares an output signal of a slave RC filter with the pre-set reference voltage. The time-to-digital converting unit(140) converts an input signal inputted from outside according to the signal outputted into a digital signal by the comparator to output the digital signal. The decoder outputs a control signal to adjust the resistance value of the main RC filter and the slave RC filter by responding to the digital signal outputted in the time-to-digital converting unit(140). The time-to-digital converting unit(140) includes a delay line unit(142) and a latch unit(144). The delay line unit(142) consists of a plurality of unit delay cells. The latch unit is connected at the output terminal of each unit delay cell and latches the digital signal inputted from each unit delay cell by responding the rising edge signal outputted in the comparer through a clock terminal. The detecting unit(146) detects edge of the digital signal outputted in the latch unit. |
