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SNOA944–February 2016
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Copyright © 2016, Texas Instruments Incorporated
Optimizing L Measurement Resolution for the LDC161x and LDC1101
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Application Report
SNOA944–February 2016
Optimizing L Measurement Resolution for the LDC161x
and LDC1101
ChrisOberhauser
ABSTRACT
TI’s LDC1612, LDC1614, and LDC1101 devices are versatile devices which use the LHR core (High-
Resolution L measurement) for Inductance measurements. This application note covers configuration
options and methods to improve the effective resolution of these devices.
Contents
1 Understanding LDC Resolution............................................................................................ 1
2 LDC Configuration Parameters ............................................................................................ 1
3 LDC Clocking................................................................................................................. 7
4 Summary...................................................................................................................... 8
1 Understanding LDC Resolution
For an ADC, the resolution is generally the number of bits in the output word, and the effective resolution
is determined from the either the INL of static linearity or from the SINAD of a full scale sinewave. If the
signal amplitude input to an ADC is less than full scale, the resolution of the output word is still the same,
but the effective resolution decreases. For example, given an ADC with an input range of 1 VPP and an
effective resolution of 16 bits, if the input signal is only 500 mVPP, then the effective resolution will usually
be halved to 15 bits.
Most inductive sensors are not able to utilize the full scale input range that TI’s LDCs provide. This results
in a reduction in the effective resolution of the system. The larger the shift in sensor inductance due to
target movement, the more effective resolution the LDC can provide. A system which has an inductance
shift of 20% will have twice the effective resolution of an equivalent system which has a 10% shift.
TI’s LDC devices measure the inductance by measuring the resonant frequency of a sensor, and so the
LDC can be considered a frequency measurement version of an ADC. Where an ADC has an LSB
measured in voltage, an LDC has an LSB measured in Hz.
For example, with an LDC system with a frequency resolution of 1 Hz (1 LSB = 1 Hz), if the sensor signal
varies by 100 kHz, then the LDC would have an effective resolution of 16.6 bits.
There are two basic approaches to increase the effective resolution – first by improving the frequency
resolution, and second by increasing the sensor frequency variation.
2 LDC Configuration Parameters
There are several LDC parameters which determine the device resolution.
2.1 Reference Count and RCOUNT
The primary device setting which determines the conversion resolution is the RCOUNT setting. A higher
value for RCOUNT corresponds to a higher resolution L measurement.
