Other Parts Discussed in Thread: PGA460
Always thank you for your help.
My name is Miyamoto of Murata Manufacturing. Thank you for specifying our ultrasonic sensor and capacitor in the evaluation board below.
I would like to ask you about the EVM (evaluation board) circuit that uses an ultrasonic sensor. In the circuit using the PGA460-Q1 device and the step-up transformer, we confirmed the circuit configuration that maximizes the sound pressure for the ultrasonic sensor. Also, in order to suppress reverberation, the impedance of the transformer secondary inductance and the placement of the tuning capacitor form a circuit configuration that can match the impedance of the ultrasonic sensor. This means matching the secondary inductance of the transformer to the resonant frequency of the transducer. Due to the structure, parasitic capacitance exists inside the ultrasonic sensor, and the capacitance increases with temperature rises. I think that this capacitance increase will be adjusted by connecting an external capacitor (tuning capacitor) in parallel with the ultrasonic sensor so that changes in impedance and resonance frequency will be small.
In addition, your company has designated the C0G characteristic product as a tuning capacitor for the capacitance change of the parasitic capacitance inside the ultrasonic sensor due to temperature rise. The C0G characteristic product is a temperature compensating capacitor whose capacitance changes little with temperature. In the C0G characteristic product as a tuning capacitor, the capacitance change is small compared to the parasitic capacitance inside the ultrasonic sensor, so we believe that the effect of tuning when temperature rises is small.
Contents of question:
◆Why is it the designation of C0G characteristic products? I would like to know the intent of tuning capacitors using C0G characteristic products.
◆ Our company also provides temperature compensation capacitors for ZLM characteristic products (characteristics in which the capacitance decreases with increasing temperature), which have the opposite characteristics to the parasitic capacitance characteristics inside the ultrasonic sensor. I think that by using ZLM characteristic products, which have the opposite characteristics of the increase in parasitic capacitance due to temperature rise, it is possible to suppress changes in overall capacitance to a small level. Why there not consideration for a ZLM characteristic product as a tuning capacitor?
◆The PGA460-Q1 device is equipped with a temperature sensor monitoring function, and has a function to connect and disconnect a temperature compensation capacitor (a tuning capacitor) at a specific temperature point to compensate for the temperature non-linearity of the transducer. Please explain this mechanism in detail.
Thank you for your guidance and answers regarding the above three points.
