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.
- Issue profile, chirp, and frame configuration APIs to set the desired chirp
sequences, including RX gain, TX power, RF frequency, and so forth.
- Perform these measurements at 0° TX phase shift to avoid TX phase shift
nonlinearity effects.
- 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:
- 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).
- 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.
- 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:
- 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.
- Use a corner reflector at 0° direction to estimate the inter-channel imbalances
across all TXm-RXn 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.
- Store the imbalance data for each index (Low Bias, Mid Bias, High Bias) in the
sensor’s non-volatile memory for in-field usage.
Table 3-1 Example (Device) Temperature
Ranges and TX/RX Gain Codes
Setting |
Temp. Range (e.g.) |
Recommended Temp Index for TX Gain Codes |
Recommended Temp Index for RX Gain Codes |
Recommended Temp Index for LO DIST Codes (Applicable for AWR2243
only) |
Low Bias |
–40°C* to 10°C |
10°C |
–40°C
(lowest of temp
range to ensure P1dB)
|
10°C |
Mid Bias |
0°C to 50°C |
50°C |
25°C
(mid temp
range)
|
50°C |
High Bias |
40°C to 140°C* |
140°C |
140°C
(highest of temp
range to ensure noise figure)
|
140°C |
Guidance |
* Limit to sensor’s in-field expected operating range |
Highest of each temp range to ensure output power |
|
|
- With this, RX gain drifts with temperature within each temperature range but
without adversely impacting noise figure and P1dB.
- 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.
- 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.
- 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.
Table 3-2 Example Structure of
Inter-Channel Imbalance Data in a 2-Chip Cascade
Device 1 |
Device 2 |
|
RX1 |
RX2 |
RX3 |
RX4 |
RX1 |
RX2 |
RX3 |
RX4 |
Low Bias |
Device 1 |
TX1 |
0 |
A12 |
A13 |
A14 |
A15 |
A16 |
A17 |
A18 |
TX2 |
A21 |
A22 |
A23 |
A24 |
A25 |
A26 |
A27 |
A28 |
TX3 |
A31 |
A32 |
A33 |
A34 |
A35 |
A36 |
A37 |
A38 |
Device 2 |
TX1 |
A41 |
A42 |
A43 |
A44 |
A45 |
A46 |
A47 |
A48 |
TX2 |
A51 |
A52 |
A53 |
A54 |
A55 |
A56 |
A57 |
A58 |
TX3 |
A61 |
A62 |
A63 |
A64 |
A65 |
A66 |
A67 |
A68 |
Mid Bias |
Device 1 |
TX1 |
0 |
B12 |
B13 |
B14 |
B15 |
B16 |
B17 |
B18 |
TX2 |
B21 |
B22 |
B23 |
B24 |
B25 |
B26 |
B27 |
B28 |
TX3 |
B31 |
B32 |
B33 |
B34 |
B35 |
B36 |
B37 |
B38 |
Device 2 |
TX1 |
B41 |
B42 |
B43 |
B44 |
B45 |
B46 |
B47 |
B48 |
TX2 |
B51 |
B52 |
B53 |
B54 |
B55 |
B56 |
B57 |
B58 |
TX3 |
B61 |
B62 |
B63 |
B64 |
B65 |
B66 |
B67 |
B68 |
High Bias |
Device 1 |
TX1 |
0 |
C12 |
C13 |
C14 |
C15 |
C16 |
C17 |
C18 |
TX2 |
C21 |
C22 |
C23 |
C24 |
C25 |
C26 |
C27 |
C28 |
TX3 |
C31 |
C32 |
C33 |
C34 |
C35 |
C36 |
C37 |
C38 |
Device 2 |
TX1 |
C41 |
C42 |
C43 |
C44 |
C45 |
C46 |
C47 |
C48 |
TX2 |
C51 |
C52 |
C53 |
C54 |
C55 |
C56 |
C57 |
C58 |
TX3 |
C61 |
C62 |
C63 |
C64 |
C65 |
C66 |
C67 |
C68 |