The imbalance measurements should be done with the AWR device in multiple calibration settings, optimized for various operating temperatures. To mitigate in-field temperature drifts, the analog settings must be reconfigured based on operating temperature. TI recommends that offset measurements at factory be done at three configurations (temperature index/indices):

• Low Bias setting – i.e., RF settings optimized for low temperatures, such as –40°C to 10°C
• Mid Bias setting – i.e., RF settings optimized for mid temperatures, such as 0°C to 50°C (approximately the factory calibration temperature)
• High Bias setting – i.e., RF settings optimized for high temperatures, such as 40°C to 140°C

The ambient temperature is still kept the same while only varying the devices’ analog configurations according to other temperature settings. The customer may fix the temperature ranges corresponding to Low Bias, Mid Bias, and High Bias settings based on the sensor’s expected in-field temperature range, allowing a small overlap for transitions.

The measurements procedure is as follows.

1. Issue profile, chirp, and frame configuration APIs to set the desired chirp sequences, including RX gain, TX power, RF frequency, and so forth.
2. Perform these measurements at 0° TX phase shift to avoid TX phase shift nonlinearity effects.
3. Set the TX gain codes, RX gain codes (and LO DIST codes for the AWR2243) with temp index corresponding to the Low Bias, Mid Bias, and High Bias settings, iteratively. An example with recommended temp indices is illustrated in Table 3-1. The recommended steps for setting the codes with desired temp indices are described below for TI's mmWave MMICs.
   • For AWR1243, AWR1843, AWR1642:
     1. Use the AWR RX GAIN TEMPLUT GET SB API and AWR TX GAIN TEMPLUT GET SB API to know the results of each device’s self-calibration algorithms for this gain, power, and RF. The output is an LUT, which is a function of temperature (in 10°C resolution).
     2. Based on the results of the above APIs, choose the RX and TX gain codes for the Low Bias, Mid Bias, or High Bias setting.
     3. Use the AWR RX GAIN TEMPLUT SET SB API and AWR TX GAIN TEMPLUT SET SB API to set the desired analog setting to each AWR device in the cascade (each device to have its individual values).
   • For AWR2243:
     1. Use AWR RUN TIME CALIBRATION CONF AND TRIGGER SB with temperature index override enabled for TX, RX, and LODIST along with respective temperature indices corresponding to Low Bias, Mid Bias, or High Bias setting.
4. Use a corner reflector at 0° direction to estimate the inter-channel imbalances across all TX_m-RX_n combinations. Measure this for each bias setting (Low Bias, Mid Bias, High Bias). An example structure of the imbalance data for a two-chip cascade is shown in Table 3-2.
5. Store the imbalance data for each index (Low Bias, Mid Bias, High Bias) in the sensor’s non-volatile memory for in-field usage.

1. With this, RX gain drifts with temperature within each temperature range but without adversely impacting noise figure and P1dB.
2. The above is an example assuming that the device temperature is 25°C during the factory measurements. Suitable adjustments may be considered if the device temperature is significantly higher and also if the application needs a different temperature range of operation.
3. The device temperature can be known from the RF INIT calibration status report (AWR_AE_RF_INITCALIBSTATUS_SB) or through device’s temperature monitoring API.
4. The transition temperatures between the settings should not be too away from the factory calibration temperature. This ensures more accurate calibration at low and high bias conditions.