Temperature compensation for RF cable assemblies
Temperature compensation is only applied to the transmitter of the RF cable assembly. Of course, receiver performance is also affected by temperature: receiver link gain is reduced at high temperatures, NF is increased; receiver link gain is increased at low temperatures, and NF is reduced. However, due to the small signal characteristics of the receiver, both gain and NF effects are within the system redundancy range.
For transmitter temperature compensation, it can also be subdivided into two parts: one is to compensate the accuracy of the transmitted signal power, and the other is to compensate the transmitter gain with temperature changes.
Modern communication system transmitters generally perform closed-loop power control (except for the slightly "old" GSM system and Bluetooth system), so the power accuracy of the transmitter calibrated by the production process depends on the accuracy of the power control loop. Generally speaking, the power control loop is a small signal loop, and the temperature stability is very high, so the temperature compensation requirement is not high unless there is a temperature sensitive device (such as an amplifier) on the power control loop.
Temperature compensation for transmitter gain is more common.
This temperature compensation is common for two purposes:
One is “visible”, usually for systems without closed-loop power control (such as GSM and Bluetooth mentioned above). Such systems usually do not require high output power accuracy, so the system can apply temperature compensation curves (functions). Keep the RF link gain within a range, so that when the baseband IQ power is fixed and the temperature changes, the RF power output by the system can also be kept within a certain range;
The other is “invisible”, usually in systems with closed-loop power control. Although the RF output power of the antenna port is precisely controlled by closed-loop power control, it is necessary to keep the DAC output signal within a certain range (most common). The example is the need for digital pre-distortion (DPD) in the base station transmit system, so the gain of the entire RF link needs to be accurately controlled to a certain value - the purpose of warming is here.
The means of transmitter temperature compensation generally have variable attenuators or variable amplifiers: when the early precision is slightly lower and the low-cost accuracy is lower, the temperature-compensation attenuator is more common; in the case of higher accuracy requirements, the solution Generally: temperature sensor + digital attenuator / amplifier + production calibration.
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