I checked the documentation of the LDC1000 and LDC1614.
But, I can figure out which one I should choose.
I want to check inductance at sampling rate around 1ksps to 10ksps.
(1) LDC1000
page 24 say
SR = 3*fsensor/(RESPONSE_TIME)
If fsensor = 2MHz
SR = 3*2*10^6/(RESPONSE_TIME)
If RESPONSE_TIME = 192
SR = 3*2*10^6/(192) = 31.25 ksps
tcx = 32 uS
If RESPONSE_TIME = 384
SR = 3*2*10^6/(384) = 15.625 ksps
tcx = 64 uS
If RESPONSE_TIME = 768
SR = 3*2*10^6/(384) = 15.625 ksps
tcx = 128 uS
If RESPONSE_TIME = 1536
SR = 3*2*10^6/(384) = 15.625 ksps
tcx = 256 uS
If RESPONSE_TIME = 3072
SR = 3*2*10^6/(384) = 15.625 ksps
tcx = 512 uS
If RESPONSE_TIME = 6144
SR = 3*2*10^6/(6144) = 976 sps
tcx = 1.024 mS
How many ENOB I can get from each configuration?
(2) LDC1614
www.ti.com/.../ldc1612.pdf
page 13 say
The conversion time represents the number of reference clock cycles used to measure the sensor frequency. It is
set by the CHx_RCOUNT register for the channel. The conversion time for any channel x is:
tCx = (CHx_RCOUNT * 16 + 4) /fREFx (6)
The reference count value must be chosen to support the required number of effective bits (ENOB). For example, if an ENOB of 13 bits is required, then a minimum conversion time of 2
13 = 8192 clock cycles is required. 8192 clock cycles correspond to a CHx_RCOUNT value of 0x0200.
So,
If ENOB = 13 bit
2^13 = 8192 = 0x2000h
CHx_RCOUNT = (2^ENOB)/16 = 2^9 = 512 = 0x0200
tcx = ((CHx_RCOUNT*16+4)/(40*10^6))
tcx = ((((2^ENOB)/16)*16+4)/(40*10^6))
tcx = (((2^ENOB)+4)/(40*10^6))
tcx = (((2^13)+4)/(40*10^6))*10^6 = 204.9 uS (sample value)
If ENOB = 11 bit
2^11 = 2048 = 0x0800
CHx_RCOUNT = (2^ENOB)/16 = 2^9 = 128 = 0x0080 (LDC1312/LDC1614 power on reset value)
tcx = (((2^ENOB)+4)/(40*10^6))
tcx = (((2^11)+4)/(40*10^6))*10^6 = 51.3 uS
If ENOB = 16 bit
tcx = (((2^16)+4)/(40*10^6))*10^3 = 1.6385 mS
By the way, CHx_RCOUNT is 16 bit, so the maximum value is
tcx = ((CHx_RCOUNT*16+4)/(40*10^6)
tcx = ((2^16)*16+4)/(40*10^6)*10^3 = 26.2145 mS
tcx = ((2^20)+4)/(40*10^6)*10^3 = 26.2145 mS ENOB = 20 bit max ?
I'm confused!