Fascinating stuff Vadim, thanks!
As expected, there's clearly a double whammy when the hand is near the antenna, where phase offset and hand C / damping both act to lower the voltage swing considerably. Wondering if that might adversely affect the sensing of phase, with the comparators having to operate over such a large dynamic range?
As expected, there's clearly a double whammy when the hand is near the antenna, where phase offset and hand C / damping both act to lower the voltage swing considerably. Wondering if that might adversely affect the sensing of phase, with the comparators having to operate over such a large dynamic range?
Good point.
Even with relatively low Q 120-Ohm R_serial inductor, sensing of hand positions near antenna may cause issues.
Better Q LC tank (e.g. 0.15 or 0.2mm wire) may give nice zoom in for long distance, but make even harder to detect out-of-resonance distance.
To reproduce on simulation, we can try to use C_hand=2pF + R_loss=10..100K Ohm
Simple solution - increasing of R_sense value.
As well, I'm trying to review symmetric rail-side sensing based on BJT current mirrors (catching difference between two VCC and GND rails current of output stage) instead of comparator sensing output current using resistor on output.
Current mirror based sensing on BJTs has a good sensitivity and performance - delay is only 2-3ns. But it's only if there is no saturation / clamping.
If output level exceeds working range, waveform is getting distorted, and delay becomes 100-200ns.
Fast comparators are expensive.
BJT current sensor may reduce sensor cost - only some output buffer is required.
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Looks nice for FPGA Theremin.
Has onboard I2S audio output.
Schematic and other useful information is already available on sipeed site.
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