Voltage-to-frequency converter with high sensitivity using all-MOS voltage window comparator
Introduction
Lots of work have been done to develop the methods for designing sensors which convey information, the values of passive or active elements, into the oscillation parameters, e.g., the magnitude, phase, frequency, or duty cycle of the vibration. The values to be conveyed might be functions of some other factors, e.g., mechanical pressure, magnetic field, or temperature. The variation of the oscillation must faithfully track the corresponding change in these factors. Hence, bandwidth, sensitivity, and linearity are the most important measures to judge the quality of these circuits. Converting the physically estimated values into oscillations is much preferred because the oscillations are more noise immune. Thus, the correctness of the information can be ensured. A traditional VCO (voltage-controlled oscillator) cannot fulfill such a demand, because the linearity and sensitivity of such a conversion are required.
This paper presents a high-bandwidth linear interfacing circuit which converts the sensed voltage into frequency. The frequency output is very much noise resistant compared to other types of outputs, e.g., the magnitude of current or voltage. It meets the requirement for integration with other IP (intellectual property), e.g., uP or communication MAC (media access circuitry). In contrast to the bipolar or BiCMOS implementations [1], [2] the proposed design is realized in TSMC (Taiwan Semiconductor Manufacturing Company) 1P5M CMOS technology. It possesses the advantages of low power, small area and high bandwidth. Although there were several prior CMOS-based converters, they either required an extra OSC [3], or additional timing control signals and many switched capacitors [4], which became overhead in those designs. By contrast, our proposed voltage-to-frequency converter (VFC) is composed of one voltage-to-current converter (-to-), and one charge and discharge circuit (CDC) which is driven by the voltage window comparator (VWC). The physical measurement of the proposed VFC on silicon shows a 0–52.95 MHz output frequency given a 0–0.9 V input range.
Section snippets
CMOS voltage-to-frequency converter
The basic theory of voltage-to-frequency conversion is to track the back-and-forth variations of a certain signal level in a pre-determined range. Thus, not only can it be easily carried out by low-cost CMOS technology, but neither external oscillators nor internal PLLs are required in the design.
Implementation of VFC on silicon
The proposed VFC is implemented by using TSMC 1P5M technology. The die photo of the physical VFC on silicon is shown in Fig. 5. The chip size is , while the core size is . The worst-case simulated working range of the input voltage is 0–0.9 V, while the output frequency is 0–55.40 MHz.
Tektronix TDS 680B oscilloscope, HP 8594E Spectrum Analyzer, and HP 1660CP Logic Analyzer are used to measure the performance of the proposed VFC. Figs. 6, 7, and 8, are the measured
Conclusion
This paper has proposed a high-bandwidth VFC. Not only are the sensitivity and output frequency dramatically improved, but the overall manufacturing cost is reduced by not using BiCMOS, and clock control circuitry. On top of these advantages, the proposed VFC consumes only 0.218 mW.
Acknowledgments
This research was partially supported by National Science Council under grant NSC 91-2218-E-110-001 and 91-2622-E-110-004. The authors would like to express their deepest gratefulness to CIC (Chip Implementation Center) of NAPL (National Applied Research Laboratories), Taiwan, for their thoughtful chip fabrication service. The authors also like to thank “Aim for Top University Plan” project of NSYSU and Ministry of Education, Taiwan, for partially supporting the research.
References (7)
- et al.
High precision voltage-to-frequency converter
- R.A. Pease, Amplitude-to-frequency converter, United States Patent no. 3746968, July 17,...
- et al.
A square-rooting voltage-to-frequency converter
IEEE Trans. Instrum. Meas.
(1997)
Cited by (14)
A High Dynamic-Range Readout Circuit with Differential Resistance-to-Time Conversion for Gas Sensor
2023, 21st IEEE Interregional NEWCAS Conference, NEWCAS 2023 - ProceedingsOn-chip CMOS Corner Detector Design for Panel Drivers*
2021, Proceedings - International SoC Design Conference 2021, ISOCC 2021Voltage-to-frequency converter for ultra-low-voltage applications
2019, 2019 42nd International Convention on Information and Communication Technology, Electronics and Microelectronics, MIPRO 2019 - ProceedingsA simple voltage-to-frequency converter with modulated duty cycle
2015, Journal of the Chinese Institute of Engineers, Transactions of the Chinese Institute of Engineers,Series AVoltage-to-frequency converters: CMOS design and implementation
2013, Voltage-to-Frequency Converters: CMOS Design and ImplementationA kind of BiCMOS voltage to frequency converter using double closed-loop interlock and adjustment control technologies
2011, Jiangsu Daxue Xuebao (Ziran Kexue Ban)/Journal of Jiangsu University (Natural Science Edition)