There are two kinds of resonators: ceramic resonators and quartz crystals. Murata has been marketing ceramic resonators under the trade name of CERALOCK for more than 30 years. The product still covers 70% of the world market. In particular, the product dominates the automotive onboard electronic component market, covering 90% of the world market. Figure 2 shows the evaluation circuit diagram of a ceramic resonator. The optimum resistance and capacitance are determined by varying the voltage and temperature applied to the IC while checking the amplitude, waveform, and margin of the oscillation. Figure 3 presents a summary of the evaluation of various ceramic resonators. Since Murata considers it necessary to ensure the normal operation of oscillator circuits as well as the stable operation of ICs, it has established the minimum amplitude of oscillation for the low-end products that may be used as the quality standards for resonators used in the automotive electronic market, whose measurements have been reported to the customers.
Next, we present three examples of the services that we have been providing for our customers. In these services, we measure not only the stability of oscillator circuits but also the performance and electronic characteristics of assembled products. The first example is the test result of the USB communication quality of a quartz crystal used in PCs such as the one used in HDDs and optical disk drives (Fig. 4). Equipment adapted for the communication protocol for USB and SATA must undergo a signal quality test to obtain authentication for communication. Murata usually obtains data that verify the signal quality in the communication for USB and SATA, in addition to the IC matching data, and submits them to its customers. This service has been contributing to reducing the evaluation man-hours in the customers’ work.
The second example is the IC matching service dedicated for devices requiring total frequency precision to be no more than ±20 ppm, which was started since volume production of the precision quartz crystals for the RF market such as Wi-Fi® started in 2014. In the RF market, the mainstream products are battery-driven assembled products such as smartphones. Manufacturers of assembled products and ICs have been trying to develop low-power devices that feature short operating periods at a time to extend a battery life. Figure 5 shows the measurement of the current consumed in the BLE module in μs timescale. Using these data for reference, manufacturers of BLE modules and ICs determine the frequency of the quartz crystals to be installed in their products and the size of their products.
The third example is the EVM measurement service for Wi-Fi® equipment. The EVM is the parameter of the precision of wireless-signal modulation. The better the EVM value, the better the quality of wireless communication. Figure 6 shows the measurement of the EVM of a Wi-Fi® module. We have been studying the possibility of the improvement of EVM by manipulating the parameters of resonator; in particular, we have been investigating the possibility of mitigating the EVM by manipulating the parameters of oscillator circuit. Recent research has revealed the parameters of resonator that improve the EVM, which have been reflected in the specification of our new products.