mhelin
Well-known member
Apart from usual analog capacitance to voltage conversion techniques (high voltage biased capsule to impedance converter or various "RF bias" methods) you could also convert the capacitance of capsule to digital directly by measuring the charge time and compare it to an internal reference (fixed capacitor). That is how for an example the ams PICOCAP capacitance-to-digital converter (CDC) works.
https://ams.com/picocap-capacitive-sensing
This chip (less than $10 in single piece quantities) can sample at 50 kHz rate with 20 bits output, and has SPI and I2C outputs:
https://www.mouser.fi/datasheet/2/588/PCap04_DS000574_2-00-1379780.pdf
I don't know any mic using that kind of digital conversion. AFAIK, Neumann's Solution-D uses a pair of conventional A/D converters 24 dB apart from each other to increase the DR.
The evaluation kit for above Picocap is too expensive, but maybe one could design own PCB for the chips available from Mouser. There is one problem though, the chip includes DSP which needs some programming. It might though be possible to use the exact procedure of capacitance measurement using some microcontroller which has fast enough GPIO and comparators available (old tiny Atmel AVRs for and example could be used to measure resistance that way overcome missing A/D converters).
There exist some Arduino applications for capacitance measurement, though those are too slow (but would be nice to have):
http://www.circuitbasics.com/how-to-make-an-arduino-capacitance-meter/
Now, the forthcoming Raspberry Pi will contain an user programmable FPGA chip with GPIO so that could be one application to try on it, though you could obviouslyuse any other FPGA. There are also many academic papers on the fast CDC's, but not being an IEEE or ACM member can't read them (for nothing), for an example:
https://ieeexplore.ieee.org/document/7833782
https://ieeexplore.ieee.org/document/5415404
https://dl.acm.org/citation.cfm?id=3057039.3057104
https://www.electronicdesign.com/analog/measure-capacitive-sensors-sigma-delta-modulator
https://ams.com/picocap-capacitive-sensing
This chip (less than $10 in single piece quantities) can sample at 50 kHz rate with 20 bits output, and has SPI and I2C outputs:
https://www.mouser.fi/datasheet/2/588/PCap04_DS000574_2-00-1379780.pdf
I don't know any mic using that kind of digital conversion. AFAIK, Neumann's Solution-D uses a pair of conventional A/D converters 24 dB apart from each other to increase the DR.
The evaluation kit for above Picocap is too expensive, but maybe one could design own PCB for the chips available from Mouser. There is one problem though, the chip includes DSP which needs some programming. It might though be possible to use the exact procedure of capacitance measurement using some microcontroller which has fast enough GPIO and comparators available (old tiny Atmel AVRs for and example could be used to measure resistance that way overcome missing A/D converters).
There exist some Arduino applications for capacitance measurement, though those are too slow (but would be nice to have):
http://www.circuitbasics.com/how-to-make-an-arduino-capacitance-meter/
Now, the forthcoming Raspberry Pi will contain an user programmable FPGA chip with GPIO so that could be one application to try on it, though you could obviouslyuse any other FPGA. There are also many academic papers on the fast CDC's, but not being an IEEE or ACM member can't read them (for nothing), for an example:
https://ieeexplore.ieee.org/document/7833782
https://ieeexplore.ieee.org/document/5415404
https://dl.acm.org/citation.cfm?id=3057039.3057104
https://www.electronicdesign.com/analog/measure-capacitive-sensors-sigma-delta-modulator