Wireless communication unit, integrated circuit and method of power control of a power amplifier therefor
A wireless communication unit comprises a transmitter having a forward path comprising a power amplifier, PA, and a feedback path operably coupled to the power amplifier, wherein the feedback path comprises a coupler arranged to feed back a portion of a signal to be transmitted and a controller logic module arranged to control a power control value of the power amplifier, such that the forward path and feedback path form a closed loop power control. The controller logic module is arranged to determine a gain variation in the transmitter and provide attenuation to a transmit signal passing therethrough on a transmit slot by transmit slot basis and instruct a power backoff where necessary.
1. A wireless communication unit comprising:
a transmitter having a forward path comprising a power amplifier and a constant gain tracking (CGT) loop, wherein a digital attenuator of the wireless communication unit is located at a starting point for a digital domain in the transmitter and a starting point for the CGT loop; and
a feedback path operably coupled to the power amplifier, wherein the feedback path comprises a coupler arranged to feed back a portion of a signal to be transmitted and a controller logic module arranged to control a power control value of the power amplifier, such that the forward path and feedback path form a closed loop power control, the controller logic module being operably coupled to both an analogue signal variable gain attenuator (SVGA) and the digital attenuator,
wherein the controller logic module is arranged to determine a gain variation in the transmitter and provide attenuation to a transmit signal passing therethrough on a transmit slot by transmit slot basis by setting an attenuator level of both the SVGA and the digital attenuator in response thereto.
2. The wireless communication unit of claim 1 wherein the transmitter further comprises an adaptive predistortion (APD) loop such that the controller logic module is arranged to determine a gain variation in the APD loop.
3. The wireless communication unit of claim 2 wherein the controller logic module is arranged to determine a running estimation of the gain variation on a transmit slot-by-transmit slot basis.
4. The wireless communication unit of claim 3 wherein the running estimation of the gain variation is estimated on a transmit slot where automatic output power control is performed after power up of the transmitter and an initial gain level applied to a signal being passed to the PA based on a slot measurement.
5. The wireless communication unit of claim 3 wherein the APD loop comprises a look-up table arranged to store a running estimation of gain variation from a nominal gain value.
6. The wireless communication unit of claim 3 wherein the controller logic module is arranged to determine a running estimation of the gain variation in at least one from a group of the following points in a transmit slot:
(i) a region where the power amplifier commences transmission on an arbitrary slot at low power;
(ii) a region where a gain variation is estimated at an end of a constant gain tracking operation; and
(iii) a region where a gain variation is estimated at an end of an APD operation.
7. A method of power control in a wireless communication unit comprising a transmitter having a forward path comprising a power amplifier, and a feedback path operably coupled to the power amplifier and comprising a controller logic module arranged to control a power control value of the power amplifier, such that the forward path and feedback path form a closed loop power control,
wherein the method comprises:
determining a gain variation in the transmitter, the transmitter including a constant gain tracking (CGT) loop, wherein a digital attenuator of the wireless communication unit is located at a starting point for a digital domain in the transmitter and a starting point for the CGT loop; and
providing attenuation, via both an analogue signal variable gain attenuator (SVGA) and the digital attenuator, to a transmit signal passing through the transmitter on a transmit slot by transmit slot basis by setting an attenuator level of both the SVGA and the digital attenuator in response to the determined gain variation.
8. The method of claim 7 further comprising:
storing a running estimation of gain variation from a nominal gain value in a look-up table of the APD loop comprises.
9. The method of claim 7 further comprising:
performing gain adjustments in both the digital domain and an analogue domain of the transmitter.
10. A wireless communication unit comprising:
a transmitter having a forward path comprising a power amplifier;
a feedback path operably coupled to the power amplifier, wherein the feedback path comprises a coupler arranged to feed back a portion of a signal to be transmitted and a controller logic module arranged to control a power control value of the power amplifier, such that the forward path and feedback path form a closed loop power control, wherein the transmitter further comprises an adaptive predistortion (APD) loop, and
wherein the controller logic module is arranged to determine a running estimation of the gain variation in the APD loop and provide attenuation to a transmit signal passing therethrough on a transmit slot by transmit slot basis; and
a digital attenuator such that the controller logic module provides attenuation to a transmit signal passing through the digital-domain attenuator on a slot by slot basis, and the transmitter including a constant gain tracking (CGT) loop, wherein the digital attenuator of the wireless communication unit is located at a starting point for a digital domain in the transmitter and a starting point for the CGT loop.
11. The wireless communication unit of claim 10 wherein the running estimation of the gain variation is estimated on a transmit slot where automatic output power control is performed after power up of the transmitter and an initial gain level applied to a signal being passed to the power amplifier based on a slot measurement.
12. The wireless communication unit of claim 10 wherein the APD loop comprises a look-up table arranged to store a running estimation of gain variation from a nominal gain value.
13. The wireless communication unit of claim 10 further comprising a signal variable gain attenuator, SVGA, such that the controller logic module provides attenuation to a transmit signal passing through the SVGA on a transmit slot by transmit slot basis by setting an attenuator level of the SVGA.
14. The wireless communication unit of claim 10 wherein the transmitter further comprises an adaptive output power control (AOC) loop such that the controller logic module is arranged to determine a gain variation in the AOC loop.
15. The wireless communication unit of claim 10 wherein the controller logic module is arranged to determine a running estimation of the gain variation in at least one from a group of the following points in a transmit slot:
(i) a region where the power amplifier PA commences transmission on an arbitrary slot at low power;
(ii) a region where a gain variation is estimated at an end of a constant gain tracking operation; and
(iii) a region where a gain variation is estimated at an end of an APD operation.
16. The wireless communication unit of claim 14 wherein the controller logic module is further arranged to perform gain adjustments in both the digital domain and an analogue domain of the transmitter.
17. A method of power control in a wireless communication unit comprising a transmitter having a forward path comprising a power amplifier and a feedback path operably coupled to the power amplifier and comprising a controller logic module logic module arranged to control a power control value of the power amplifier, such that the forward path and feedback path form a closed loop power control, wherein the transmitter further comprises an adaptive predistortion (APD) loop;
wherein the method comprises:
determining a running estimation of the gain variation in the APD loop; and
providing attenuation to a transmit signal passing through the transmitter on a transmit slot by transmit slot basis, the transmitter including a constant gain tracking (CGT) loop, wherein the digital attenuator of the wireless communication unit is located at a starting point for a digital domain in the transmitter and a starting point for the CGT loop.
18. The wireless communication unit of claim 1 wherein the transmitter further comprises an adaptive output power control (AOC) loop such that the controller logic module is arranged to determine a gain variation in the AOC loop.
19. The method of claim 17 further comprising:
storing a running estimation of gain variation from a nominal gain value in a look-up table of the APD loop comprises.
20. The method of claim 17 further comprising:
performing gain adjustments in both the digital domain and an analogue domain of the transmitter.