Single-chip optoelectronic rangefinder using PIN-photodiode and correlated active integration

摘要

Integrated optical distance measurement systems based on the Time-of-Flight (TOF) principle open up 3D vision for various applications like e.g. inspection systems. The introduced single pixel consists of both, a PIN photodiode and a signal-processing circuit on chip. Due to eye-safety reasons, the optical illumination power is limited (Popt<2mW). For diffuse reflecting objects in distances up to several meters, signal attenuation of about -50dB occurs with 1-inch optics. Therefore high responsivity of the photodiode is required: R=0.36A/W at 660nm. Resolutions of centimeters matter TOF far below 1ns, i.e. the photodiode has to feature high bandwidth (f3dB=1.35GHz). Distance information is gained by correlation between the modulated transmission signal and the run- ime delayed, attenuated received signal. The readout circuit consists of three stages: the first stage is a broadband current amplifier, realised with current mirrors. The correlation is performed in the second stage by a switching mixer. Amplification and smoothing is performed in the third, active integrator stage. The distance information is derived from the output signal by external sampling and simple data processing. A standard deviation of better than 1% (2%) for distances up to 2m (3.7m) is achieved for measurement durations of 10ms. The primary linearity error of less than 6cm is educed by error correction. The pixel has a fill factor of ~10%, including the overall pixel area of ~460?m?170?m and the photodiode with a diameter of 100?m. The chip was realised in a 0.6?m BiCMOS ASIC process.