Method for time of flight modulation frequency detection and illumination modulation frequency adjustment

Abstract

A method removing adjecent frequency interference from a Time Of Flight sensor system by adaptively adjusting the transmitted infrared illumination frequency of the TOF sensor by measuring the interfering infrared illuminating frequencies and dynamicaly adjusting the transmitted illuminating infrared frequency of the TOF sensor to eliminate the interference.

Claims

1. A method of interference rejection in a Time of Flight (TOF) measurement system including a transmitted infrared illumination modulating frequency comprising the steps of: receiving all ambient infrared illumination; measuring the modulation frequencies of said received infrared illumination; comparing duration of said measured modulation frequencies to a preset threshold; adjusting the transmitted infrared illumination modulating frequency of the Time of Flight measurement system if the preset threshold is exceeded.

2. The method of claim 1 wherein: the TOF measurement system's transmitted infrared illumination modulation frequency is dynamically adjusted to a value that is offset from the strongest detected ambient infrared modulation frequency.

3. The method of claim 1 wherein: the TOF measurement system's transmitted infrared illumination modulation frequency is dynamically adjusted to a value that is offset from a plurality of the detected ambient infrared modulation frequencies.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) These and other aspects of this invention are illustrated in the drawings, in which:

(2) FIG. 1 shows the prior art TOF distance measurement;

(3) FIG. 2 illustrates the block diagram of the present invention.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

(4) A TOF (Time Of Flight) sensor delivers a very accurate depth measurement and can be widely applied to applications within various environments. However, TOF sensor technology intrinsically has a cross interference problem among TOF sensors due to IR illuminations from multiple TOF sensors employing the same modulation frequency. Since IR modulation frequency is directly related to a covered depth range of TOF, there is the likelihood that the same modulation frequency of TOF IR illumination will be selected among TOF sensors in place.

(5) For example, for applications targeting a mid range depth map, in many cases a 20 MHz IR modulation frequency is chosen. Interference from TOF sensors with the same IR modulation frequency (20 MHz) can significantly impact on depth accuracy of each sensor.

(6) The described invention provides a method to avoid IR interference among TOF sensors by combining the IR modulation frequency detector with logic for dynamic adjustment of the IR transmission modulation frequency.

(7) As shown in FIG. 2, the invention consists of mainly two parts, the AIMD (Ambient IR Modulation-frequency Detection) module and TIMA (Transmission IR Modulation-frequency Adjustment) module.

(8) The AIMD module detects all ambient IR modulation-frequencies 208 by IR frequency detector 201, and MCU 202 analyzes each modulation frequency and its duration time by IR Modulation Frequency Monitoring Routine 203. If its duration Δtime(f.sub.r,IR) is longer than a predefined threshold Th.sub.Δtime, the MCU triggers IR Modulation Frequency Adjusting Routine 207 to adjust the current IR transmission modulation frequency 209 of the associated TOF sensor. The predefined threshold can be dynamically re-configured to adjust the sensitivity of TOF to interference noise and the requirement for real-time processing.

(9) A minor change of IR modulation frequency 209 (e.g. 20 Mh->20.1 Mhz) can significantly reduce the interference related noise. Thus, the interference of ambient IR modulation frequencies can be removed in the depth map acquisition of TOF sensor 205. As a result, TOF sensor raw data 210 can be captured without ambient cross-interference noise.