Biases (Sensor Settings)

Each of Prophesee’s sensors can be tuned for different application requirements and conditions (higher speed, lower background activity, higher contrast sensitivity, etc) via a set of settings that we call biases. All biases values can not be applied on a sensor. Each sensor generation supports its range of biases values.

Bias Tuning on Gen3 Sensor

The following user biases can be adjusted:

  • Photodiode bandwidth (bias_pr) sets the operating point of the photoreceptor feedback amplifier (by adjusting the “bias_pr” voltage, in mV). High “bias_pr” value leads to small bias currents in the amplifier and also limits the bandwidth of the photoreceptor.

  • Buffer bandwidth (bias_fo) sets the bandwidth of the post-photoreceptor source follower buffer stage (by adjusting the “bias_fo” voltage, in mV). It is useful to control noise events i.e. background activity. Decreasing “bias_fo” value will increase the bandwidth (make the sensor faster) and also increase the background noise. Increasing “bias_fo” value will decrease both speed and noise.

  • Deadtime (bias_refr) sets the “refractory period” during which the Change Detector (sampler) is switched off after generating an event (it has sampled). This parameter controls the sampling rate of the pixels and hence the output data rate of the sensor.

  • Contrast sensitivity biases (bias_diff, bias_diff_on, bias_diff_off) control the light sensitivity of the sensor, so that the sensor’s pixels are triggered when there is a required difference of illumination (i.e. contrast). The contrast sensitivity is expressed as the difference between “bias_diff_on” and “bias_diff” values (for positive light changes) and “bias_diff” and “bias_diff_off” values (for negative light changes). “bias_diff” stands for the threshold reference voltage and should not be modified. To adjust the contrast sensitivity:

    • approach “bias_diff_on” value to “bias_diff” (decrease the difference) to increase the sensitivity to positive light changes

    • approach “bias_diff_off” values to “bias_diff” (decrease the difference) to increase the sensitivity to negative light changes

  • High-Pass Filter (bias_hpf) controls the strength of a High-Pass Filter that removes low frequency noise (spontaneous background activity). With low “bias_hpf” values, high frequencies are filtered out, but if the the value is too low, the quality of the signal can be impacted.

Note

When setting biases outside of the supported range, the biases values are rounded to a supported range.

For more information on the gen3 biases, please, see [Posch11].

To get information about the gen4 biases, contact us to receive the sensor datasheet.

BIAS file

Biases values can be adjusted via a file with a .bias extension, that can be used in Metavision SDK.

The BIAS file stores the values of the biases.

Several BIAS files are deployed within Prophesee’s software. For example, after installing Metavision SDK, several BIAS files can be found in “<install-prefix>/share/metavision/sdk/driver/biases/”. Those BIAS files store default biases settings for every sensor generation.

Please, note that in addition to the main biases described in this section, the pre-installed BIAS files could contain other biases which should not be modified.