Successive approximation register (sar) analog-to-digital converter (adc), radar unit and method for improving harmonic distortion performance

A radar unit comprising at least one antenna coupled to at least one radio frequency circuit configured to receive and down-convert received radar signals, wherein the radar unit comprises a baseband circuit having a successive approximation register, SAR, analog-to-digital converter, ADC, arranged to receive a down-converted baseband received radar signal and convert the down-converted baseband received radar signal to a digital form, wherein the SAR ADC comprises:

• a track and hold circuit configured to sample an analog input signal;
• a comparator coupled to the track and hold circuit and configured to compare the sampled analog input signal with a reference voltage;
• and
• a feedback path that comprises a digital to analog converter, DAC, configured to generate the reference voltage that approximates the input analog signal, such that the comparator determines a sign of a subtraction operation between the sampled input and DAC output;
• a dither circuit coupled to the feedback path and arranged to add a dither signal at the input of the DAC in a first time period and subtract the dither signal from the output digital signal routed via the feedback path and input of the DAC in a second time period during a conversion phase of the SAR ADC.

A method for digitizing a received analog input signal in a successive approximation register, SAR, analog-to-digital converter, ADC, wherein the method comprises:

• sampling an analog input signal by a track and hold circuit;
• comparing the sampled analog input signal with a DAC output voltage by a comparator;
• and
• generating, by a digital to analog converter, DAC, the voltage that approximates the input analog signal;
• adding a dither signal at an input of the DAC in a first time period and
• subtracting the dither signal from the output digital signal routed via a feedback path and input of the DAC in a second time period during a conversion phase of the SAR ADC.