A Frequency Multiplier Based Isometric Sampler for Second-Order Transfer Functions with Wide Frequency Variation Range

Second-order transfer functions can offer a high gain bandwidth for improving control performance. However, the variation in input frequency may curtailing its gain performance. This paper presents a frequency multiplier-based isometric sampler for adapting the variation in input frequency. Since the sampling interval is isometric rather than regular timing sampling, the product of the sampling time and the desired resonant frequency could be remained constant. To speed up the alignment between the input frequency and resonant frequency, a variable divisor was presented to reduce the external clock frequency toward the target of boost frequency. The proposed sampler was verified by the UMC 1P6M 0.18 µm CMOS process. Experimental result shows that the proposed sampler is adaptive to the input frequency variation in the range of 15 Hz to 200 Hz under various boost frequency ratios.