Transmitter gain control and calibration
Embodiments provide improved systems and methods of gain control and calibration for wireless transmitters. In particular, embodiments allow linear gain control over the entire transmitter gain control range, independent of temperature/process variations. Embodiments require very low power consumption compared to existing approaches. Embodiments may also be used for gain control calibration during production time, thereby substantially reducing production calibration time and cost.
1. A system, comprising:
a digital module configured to receive an input signal;
an analog module, coupled to the digital module, configured to generate an output signal of the system based on the input signal, wherein a level of the output signal is adjustable by the digital module or the analog module; and
a feedback module, coupled between the analog module and the digital module;
wherein the feedback module is active when the level of the output signal is above a pre-defined level, and inactive when the level of the output signal is below the pre-defined level, and
wherein the feedback module is also active during a transition in the level of the output signal from a first level to a second level that is below the pre-defined level when a gain change in the analog module is required to implement the transition.
2. The system of claim 1 , wherein when the feedback module is active, the digital module is configured to compensate for differences between the output signal and a desired output signal, and wherein the differences are due to variations in a nominal gain of the analog module.
3. The system of claim 1 , wherein the gain change causes a maximum output level error to be exceeded when made without activating the feedback module.
4. The system of claim 1 , wherein the system is configured to operate in a closed loop power control (CLPC) mode when the level of the output signal is above the pre-defined level and to operate in an open loop power control (OLPC) mode when the level of the output signal is below the pre-defined level, and wherein the transition is from the CLPC mode to the OLPC mode.
5. The system of claim 1 , wherein the system is configured to operate in a closed loop power control (CLPC) mode when the output signal is above the pre-defined level and to operate in an open loop power control (OLPC) mode when the output signal is below the pre-defined level, and wherein the transition is within the OLPC mode.
6. The system of claim 1 , wherein the feedback module is configured to be inactive after the transition is implemented.
7. The system of claim 3 , wherein the transition in the level of the output signal is equal to 1 dB, and wherein the maximum output level error is equal to ±0.5 dB.
8. The system of claim 1 , wherein the system is a transmitter, and wherein the digital module includes a baseband processor, a digital-to-analog converter (DAC), or a digital state machine.
9. The system of claim 1 , wherein the system is a transmitter, and wherein the analog module includes a modulator, a driver circuit, a power amplifier, or a filter.
10. The system of claim 1 , wherein the system is a transmitter, and wherein the feedback module includes a power amplifier (PA) detector, a radio frequency (RF) envelope detector, an analog-to-digital converter (ADC), or a digital gain control circuit.
11. A transmitter, comprising:
a feed-forward path, including a digital module and an analog module configured to produce an output signal of the transmitter; and
a feedback path, coupled to an output of the feed-forward path,
wherein the transmitter is configured to operate in an open loop power control (OLPC) mode or in a closed loop power control (CLPC) mode based on a target output power level of the output signal and a dynamic range of the power detector, and
wherein, when the target output power level requires adjusting a gain of the analog module and the transmitter operating in the OLPC mode, the feedback path is, configured to measure the output signal to generate a measured output power level with the transmitter operating, in the OLPC mode, and the digital module is configured to compensate for a difference between the measured output power level and the target output power level.
12. The transmitter of claim 11 , wherein the feedback path further includes a digital gain control circuit.
13. The transmitter of claim 12 , wherein the feedback path further includes a power detector, and wherein the transmitter is configured to operate in the CLPC mode when the target output power level is within the dynamic range of the power detector.
14. The transmitter of claim 13 , wherein when the transmitter operates in the CLPC mode, the power detector is configured to measure the output signal to generate a measured output signal, and the digital gain control circuit is configured to generate a control signal for controlling the digital module based on the measured output signal.
15. The transmitter of claim 12 , wherein the feedback path further includes a power detector, and wherein the transmitter is configured to operate in the OLPC mode when the target output power level is outside a range of powers that can be measured with accuracy by the power detector.
16. The transmitter of claim 11 , wherein the measured output power level is generated by controlling the analog module to produce the target output power level.
17. The transmitter of claim 11 , wherein the feedback path further includes a power detector configured to measure the output signal to produce the measured output power level.
18. The transmitter of claim 11 , wherein the feedback path further includes an envelope detector configured to measure the output signal to produce the measured output power level.
19. A transmitter, comprising:
a digital module configured to produce a digital signal;
an analog module, coupled to the digital module, configured to produce an analog signal based on the digital signal;
a power amplifier (PA) configured to produce an output signal based on the analog signal; and
a power detector coupled to an output of the PA,
wherein when the output signal is within a dynamic range of the power detector, the power detector is configured to measure the output signal to produce a first measured output signal, and the digital module is configured to produce the digital signal responsive to the first measured output signal, and
wherein when the output signal is outside the dynamic range of the power detector, the power detector is configured to measure the output signal to produce a second measured output signal, and the digital module is configured to produce the digital signal responsive to a difference between the second measured output signal and a target output signal.
20. The transmitter of claim 19 , wherein the target output signal is outside the dynamic range of the power detector.