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Gen1 (AWR1243, AWR1843, AWR1642, and AWR1443) and Gen2 (AWR2243) radar devices include self-calibrations to mitigate process and temperature effects on analog performance. The calibrations include RF INIT (i.e., boot time) calibrations to mitigate manufacturing process variation effects, and Run Time calibrations to mitigate temperature effects. These calibrations mostly involve optimizing the RF register settings for TX, RX, and LO-based on the temperature read by the built-in temperature sensors. In simple single-chip usage context, these self-calibrations achieve the purpose of analog performance stabilization without compromising on inter-channel imbalances due to inherent channel matching within each device.
Maintaining inter-channel matching in multi-device cascaded sensors is more challenging due to manufacturing process mismatches across devices and independence of the self-calibration procedures running in the multiple devices. This note describes recommendations to improve a cascade system’s coherence across time and temperature and involves more control of AWR devices by the host processor on the sensor. Further, the recommended procedures may also be used in advanced single chip applications which desire stability of the radar return signal’s absolute phases across radar frames, devoid of abrupt jumps.
Further, the recommendations in this note also address the topic of avoiding corruption of the self-calibration results when the device operates in interference-prone environments. Note that the same is also briefly explained in Self-Calibration in TI’s mmWave Radar Devices (SPRACF4), applicable in single chip usages. Finally, another important topic addressed in this note is TX phase shifters (AWR1843 and AWR2243). Their accuracies can be improved with calibrations at customer factory as well as in field, and this note describes relevant recommendations.
In single chip usage context, in interference-free environments, all self-calibrations can be enabled, including the RF INIT calibrations and Run Time calibrations. Typically, the host is expected to trigger RF INIT calibrations once at the beginning of each power cycle. The host also enables run-time calibrations by configuring the device to self-trigger calibration updates at a configurable periodicity (for example, once in N number of frames, amounting to ~1 second). The device then schedules auto-periodic calibrations, with a 10°C hysteresis to avoid unnecessary successive retriggers. Alternately, the host may also explicitly trigger Run Time calibration after it senses a significant temperature change (for example, ~30°C).
These calibrations do not disturb any inter-channel imbalances in single-chip context due to inherent channel matching within each device. But the situation is different in cascade systems and in advanced single-chip usages. In cascade usage, this note provides guidelines to mitigate process and temperature variation effects without disturbing inter-channel imbalances. This note also provides guidelines to enable advanced single chip usages that desire stability of radar return signal’s absolute phase over time across frames.
Further, in typical automotive usages, where interference from other radars can be expected, some of these calibrations are discouraged to be used in field, to avoid interference corrupted calibration results. The recommendations in this note avoid running in-field those RF INIT or Run Time calibrations that are susceptible to interference corruption. Instead, some calibration procedures in interference-free customer factory (one time per device) and other temperature adjustment procedures in-field are recommended.
TX phase shifter accuracies can also be improved with similar calibration approaches. These are relevant in interference and cascade contexts.