Innovative frequency measurement technique used in the design of a single channel frequency to digital converter ASIC
Neranjen Ramalingam, Vijay K. Varadan, V. V. Varadan · Smart Materials and Structures · 1999
The frequency to digital converter (FDC) is an application specific integrated circuit (ASIC). The chip has been designed to handle one input channel but can easily be expanded to handle multiple channels of frequencies. The channel is capable of measuring frequencies from 100 Hz to 100 kHz. The power consumption of the chip is very low. The frequency measurement accuracy is better than 0.1%. The conversion rate per channel is 100 samples which can be varied too. The chip has built in test equipment (BITE) to verify its operation. It is able to generate frequencies like 8, 4, 2 and 1 MHz which can be fed as optional clock frequencies depending on the accuracy desired. The FDC chip can be interfaced to a 16 bit bus. To meet these stringent specifications of the FDC chip an innovative frequency measurement technique has been devised called the hybrid technique of frequency measurement. The technique proves to be very accurate and it is found that by varying the sampling rate the range of input frequencies over which this accuracy can be achieved also changes. The specifications are particularly strict so that it is possible to use the chip for any military application for which a very reliable operation is demanded. The FDC chip is hence ideal for control and guidance purposes. The chip has wide ranging applications. In conjunction with sensors such as accelerometers it can be used to design smart sensors. The chip can play a vital role in engine controllers and in pressure measurements using vibration type transducers. Sometimes to isolate (galvonic) transducers, the output is converted to frequency and isolation is achieved using opto-isolators; then by measuring the frequency using this chip this can be converted to digital information.