Laser distance measuring module with INL error compensation
A distance measuring method and an electronic laser distance measuring module, in particular for use in a distance measuring apparatus, especially configured as a laser tracker, tachymeter, laser scanner, or profiler, for fast signal detection with an analog-to-digital converter, wherein conversion errors that arise in the context of a signal digitization, in particular timing, gain and offset errors of the ADC, are compensated for by means of variation of the sampling instants.
1. A distance measuring method for determining a distance to a target object, the method comprising:
emitting transmission signals as a transmission signal series;
receiving at least portions of the transmission signals of the transmission signal series reflected at the target object as reception signals of a reception signal series;
digitizing the reception signals of the reception signal series into digital signals of a digital signal series using an interleave or pipeline analog-to-digital converter, referred to hereinafter as ADC, and
processing the digital signal series in order to derive the distance to the target object therefrom,
wherein the reception signal series is superimposed with a bias signal that varies in a defined manner, wherein a value of the bias signal is varied over time in such a way that reception signals of the reception signal series are superimposed with different offset values within a defined value range.
2. The distance measuring method according to claim 1 , wherein the different offset values are taken into account during the processing of the digital signal series in order to compensate for an average integral non-linearity of the ADC as a function of a signal value of an ADC input signal.
3. The distance measuring method according to claim 1 , wherein the bias signal is configured as a signal having a low-frequency oscillation component.
4. The distance measuring method according to claim 1 , wherein:
the bias signal is generated by means of at least one of the following measures:
adding different discrete DC values to an ADC input signal of an ADC input signal series generated by the reception signal series at different instants of the ADC input signal series referred to hereinafter as DAC,
periodically shifting offset levels of a common-mode voltage of the ADC, and
a noise generator for generating a variable additional signal to the ADC input signal series.
5. The distance measuring method according to claim 1 , wherein the value range of the bias signal is set on the basis of:
a defined measurement accuracy for the determination of the distance, or
a measured signal value of a reception signal.
6. An electronic laser distance measuring module for determining a distance to a target object comprising:
a transmission channel having a transmitting unit for generating transmission signals of a transmission signal series;
a reception channel having a receiving unit for receiving at least portions of the transmission signals of the transmission signal series reflected at the target object as reception signals of a reception signal series;
a reception circuit for digitizing the reception signals of the reception signal series into digital signals of a digital signal series with an interleave or pipeline analog-to-digital converter, referred to as ADC hereinafter; and
a supervisory and control unit for determining the distance to the target object on the basis of a processing of the digital signal series, in particular summing or averaging the digital signals over the digital signal series, in particular wherein the determination of the distance is based on the pulse time-of-flight method,
wherein the laser distance measuring module is configured in such a way that:
a bias signal that varies in a defined manner is generated, and
the reception signal series is superimposed with the bias signal, wherein a value of the bias signal is varied over time in such a way that reception signals of the reception signal series are superimposed with different offset values within a defined value range.
7. The laser distance measuring module according to claim 6 , wherein the different offset values are taken into account during the processing of the digital signal series by the supervisory and control unit in order to compensate for an average integral nonlinearity of the ADC as a function of a signal value of an ADC input signal.
8. The laser distance measuring module according to claim 6 , wherein the bias signal is configured as a signal having a low-frequency oscillation component.
9. The laser distance measuring module according to claim 6 , wherein the bias signal is generated by means of at least one of the following measures:
adding different discrete DC values to an ADC input signal of an ADC input signal series generated by the reception signal series at different instants of the ADC input signal series, referred to hereinafter as DAC,
periodically shifting offset levels of a common-mode voltage of the ADC, and
a noise generator for generating a variable additional signal to the ADC input signal series.
10. The laser distance measuring module according to claim 6 , wherein the value range of the bias signal is set on the basis of:
a defined measurement accuracy for the determination of the distance, or
a measured signal value of a reception signal.