I'm trying to integrate this ultrasonic sensor into my design and create the necessary circuitry for it. I asked CUI, the manufacturer, for any reference designs/guides for it and they sent me a pdf with a circuit that is attached here.
Between that, running it through Spice sim in Eagle, and the "PC Services" breakdown about another ultrasonic sensor found here I've been trying to fully understand what is going on and feel like I mostly understand, except for calculation of the resistors and caps for the band pass filter, which I would like to verify to make sure the resonant frequency of the filter is 48kHz to match the CUI device.
The bulk of the circuits and values in each example are nearly identical to one another, except for the resistor on the output of the op amp that makes up the band pass stage, one is 7.5k and the other 10k, but I don't think that has much effect on the filter stage itself. Also, one uses a separate transducer for Tx and Rx, while the CUI uses the same transducer for both Tx and Rx (at least that's what I've come to understand).
I've followed along some videos about IGMF filters like the one found here as well as this tutorial, but I can't make sense of the values I calculate as a result and the ones given in the schematics mentioned above, and don't know if its even possible to analyze the band pass filter stage outside of the context of the rest of the amplifier stages. Additionally, I've run the circuit through Spice Sim in Eagle, one with almost the whole circuit and one with just the band pass filter and have attached the results.
As you can see from the IGMF filter spice sim attached, using the values given I got the resonant frequency to be about 18kHz. When I change R5 in that circuit to 10k instead of 75k I get it to center near 48kHz, but that doesn't make sense to me computationally. I found the formula R' = R(fc/fc')^2 for adjusting the value of R4 where f and R are values for a given functional circuit and and f' and r' are just translations of values for a different frequency.
Using this I calculated R4 in that same circuit to be 694Ω, but this doesn't match sim. Additionally, working with the schematic in the IGMF filter spice attachment and following along the YouTube video mentioned above, I calculated R3 = 31.8k, R4 = 170Ω, and R5=63.7Ω, but none of these results match any of the sims I've run.
Can anyone provide me some insight about this circuit and the proper way to calculate/verify the values needed for resonant frequency of 48k. Ideally I would like to use values as close to the ones in the example schematics.
Thanks!
P.S. That was perhaps a verbose and convoluted description of my problem so please let me know if you need any clarification of what I'm asking or the process I've used to try and understand things.
Between that, running it through Spice sim in Eagle, and the "PC Services" breakdown about another ultrasonic sensor found here I've been trying to fully understand what is going on and feel like I mostly understand, except for calculation of the resistors and caps for the band pass filter, which I would like to verify to make sure the resonant frequency of the filter is 48kHz to match the CUI device.
The bulk of the circuits and values in each example are nearly identical to one another, except for the resistor on the output of the op amp that makes up the band pass stage, one is 7.5k and the other 10k, but I don't think that has much effect on the filter stage itself. Also, one uses a separate transducer for Tx and Rx, while the CUI uses the same transducer for both Tx and Rx (at least that's what I've come to understand).
I've followed along some videos about IGMF filters like the one found here as well as this tutorial, but I can't make sense of the values I calculate as a result and the ones given in the schematics mentioned above, and don't know if its even possible to analyze the band pass filter stage outside of the context of the rest of the amplifier stages. Additionally, I've run the circuit through Spice Sim in Eagle, one with almost the whole circuit and one with just the band pass filter and have attached the results.
As you can see from the IGMF filter spice sim attached, using the values given I got the resonant frequency to be about 18kHz. When I change R5 in that circuit to 10k instead of 75k I get it to center near 48kHz, but that doesn't make sense to me computationally. I found the formula R' = R(fc/fc')^2 for adjusting the value of R4 where f and R are values for a given functional circuit and and f' and r' are just translations of values for a different frequency.
Using this I calculated R4 in that same circuit to be 694Ω, but this doesn't match sim. Additionally, working with the schematic in the IGMF filter spice attachment and following along the YouTube video mentioned above, I calculated R3 = 31.8k, R4 = 170Ω, and R5=63.7Ω, but none of these results match any of the sims I've run.
Can anyone provide me some insight about this circuit and the proper way to calculate/verify the values needed for resonant frequency of 48k. Ideally I would like to use values as close to the ones in the example schematics.
Thanks!
P.S. That was perhaps a verbose and convoluted description of my problem so please let me know if you need any clarification of what I'm asking or the process I've used to try and understand things.
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