Distance sensing by IQ domain differentiation of time of flight (TOF) measurements
View Patent ↗A system and method for identifying a position of a moving object, regardless of static objects present in the optical field of an active infrared (IR) proximity detector, is provided. Moreover, a modulated light emitting diode (LED) signal is captured and processed through I/Q demodulation. Specifically, the reflections received at an IR sensor are demodulated to generate in-phase (I) and quadrature phase (Q) signals and the derivative of I/Q signals is obtained to isolate motion. For example, an I/Q domain differentiator or a high pass filter is employed to calculate the derivative, which actively remove the effects of all forms of static interference. Further, the phase of the derivative I/Q signals is determined and is utilized to reconstruct the distance at which the motion occurred.
1. A method for determining at least one of a distance or presence of one or more moving objects, the method comprising:
(a) receiving in-phase (I) and quadrature-phase (Q) signals that were produced by performing quadrature demodulation of a sensor signal indicative of a portion of a light signal that was reflected from one or more objects;
(b) determining derivatives of the in-phase (I) and quadrature-phase (Q) signals;
(c) determining a phase of the derivatives of the in-phase (I) and quadrature-phase (Q) signals; and
(d) determining at least one of a distance or presence of one or more moving objects in dependence on the phase of the derivatives of the in-phase (I) and quadrature-phase (Q) signals.
2. The method of claim 1 , wherein:
step (b) is performed using analog circuitry configured to determine derivatives of the in-phase (I) and quadrature-phase (Q) signals.
3. The method of claim 2 , wherein:
step (b) includes low pass filtering outputs of the analog circuitry configured to determine derivatives of the in-phase (I) and quadrature-phase (Q) signals to thereby filter out at least some noise introduced by the analog circuitry.
4. The method of claim 1 , wherein the in-phase (I) and quadrature phase (Q) signals received at step (a) are analog signals, and wherein step (b) includes:
converting the in-phase (I) and quadrature-phase (Q) signals into digital in-phase (I) and quadrature-phase (Q) signals, respectively;
determining the derivative of the digital in-phase (I) signal by subtracting a delayed value of the digital in-phase (I) signal from a current value of the digital in-phase (I) signal; and
determining the derivative of the digital quadrature-phase (Q) signal by subtracting a delayed value of the digital quadrature-phase (Q) signal from a current value of the digital quadrature-phase (Q) signal.
5. The method of claim 4 , wherein the subtracting are performed in accordance with a variable sampling rate that ensures that results of the subtracting are at least as large as a threshold value.
6. The method of claim 1 , wherein the in-phase (I) and quadrature phase (Q) signals received at step (a) are digital signals, and wherein step (b) includes:
determining the derivative of the in-phase (I) signal by subtracting a delayed value of the in-phase (I) signal from a current value of the in-phase (I) signal; and
determining the derivative of the quadrature-phase (Q) signal by subtracting a delayed value of the quadrature-phase (Q) signal from a current value of the quadrature-phase (Q) signal.
7. The method of claim 6 , wherein the subtracting are performed in accordance with a variable sampling rate that ensures that results of the subtracting are at least as large as a threshold value.
8. A subsystem for use with a further subsystem, the further subsystem including a driver configured to produce a drive signal that drives a light emitting element to thereby cause a light signal to be emitted, an optical sensor configured to produce a sensor signal that is indicative of a portion of the light signal that reflects from one or more objects and is incident on the optical sensor and a demodulator configured to perform quadrature demodulation of the sensor signal to produce in-phase (I) and quadrature phase (Q) signals, the subsystem comprising:
a differentiator configured to determine derivatives of the in-phase (I) and quadrature phase (Q) signals from the demodulator;
a phase detector configured to determine a phase of the derivatives of the in-phase (I) and quadrature phase (Q) signals; and
circuitry configured to use the phase of the derivatives of the in-phase (I) and quadrature phase (Q) signals to determine at least one of a distance or presence of one or more moving objects within a sensor field of the optical sensor.
9. The subsystem of claim 8 , wherein when there are one or more moving objects and one or more static objects within a sensor field of the optical sensor:
the derivatives of the in-phase (I) and quadrature-phase (Q) signals determined by the differentiator are indicative of reflections from one or more moving objects and are generally not indicative of reflections from one or more static objects within the sensor field of the optical sensor.
10. The subsystem of claim 8 , further comprising:
circuitry configured to use the phase of the derivatives of the in-phase (I) and quadrature phase (Q) signals to calibrate further circuitry configured to determine at least one of a distance or presence of one or more moving objects based on non-differentiated in-phase (I) and quadrature phase (Q) signals;
wherein the calibration compensates for one or more static objects within a sensor field of the optical sensor.
11. The subsystem of claim 8 , wherein the differentiator comprises analog circuitry configured to determine derivatives of the in-phase (I) and quadrature phase (Q) signals.
12. The subsystem of claim 11 , wherein the differentiator further comprises a low pass filter configured to low pass filter outputs of the analog circuitry configured to determine derivatives of the in-phase (I) and quadrature phase (Q) signals to thereby filter out at least some noise introduced by the analog circuitry.
13. The subsystem of claim 8 , wherein the differentiator includes:
an analog-to-digital converter (ADC) configured to convert the in-phase (I) signal produced by the demodulator into a digital in-phase (I) signal;
an analog-to-digital converter (ADC) configured to convert the quadrature-phase (Q) signal produced by the demodulator into a digital quadrature-phase (Q) signal;
circuitry configured to subtract a delayed value of the digital in-phase (I) signal from a current value of the digital in-phase (I) signal; and
circuitry configured to subtract a delayed value of the digital quadrature-phase (Q) signal from a current value of the digital quadrature-phase (Q) signal.
14. The subsystem of claim 13 , wherein the circuitry configured to subtract a delayed value of the digital in-phase (I) signal from a current value of the digital in-phase (I) signal, and the circuitry configured to subtract a delayed value of the digital quadrature-phase (Q) signal from a current value of the digital quadrature-phase (Q) signal, each perform said corresponding subtraction in accordance with a fixed sampling rate.
15. The subsystem of claim 13 , wherein the circuitry configured to subtract a delayed value of the digital in-phase (I) signal from a current value of the digital in-phase (I) signal, and the circuitry configured to subtract a delayed value of the digital quadrature-phase (Q) signal from a current value of the digital quadrature-phase (Q) signal, each perform said corresponding subtraction in accordance with a variable sampling rate that ensures that results of the subtracting are at least as large as a threshold value.
16. The method of claim 1 , further comprising:
(e)using the phase of the derivatives of the in-phase (I) and quadrature-phase (Q) signals to calibrate circuitry that determines at least one of a distance or presence of one or more moving objects based on non-differentiated in-phase (I) and quadrature-phase (Q) signals in a manner that compensates for one or more static objects.