Classifications

• • H—ELECTRICITY
  • H03—ELECTRONIC CIRCUITRY
  • H03G—CONTROL OF AMPLIFICATION
  • H03G3/00—Gain control in amplifiers or frequency changers
  • H03G3/20—Automatic control
  • H03G3/30—Automatic control in amplifiers having semiconductor devices
  • H03G3/3036—Automatic control in amplifiers having semiconductor devices in high-frequency amplifiers or in frequency-changers
  • H03G3/3042—Automatic control in amplifiers having semiconductor devices in high-frequency amplifiers or in frequency-changers in modulators, frequency-changers, transmitters or power amplifiers
  • H03G3/3047—Automatic control in amplifiers having semiconductor devices in high-frequency amplifiers or in frequency-changers in modulators, frequency-changers, transmitters or power amplifiers for intermittent signals, e.g. burst signals

Definitions

• the present disclosure relates to power control systems, and more particularly to adaptive power control systems that do not require factory calibration of loop control parameters.
• transmit (Tx) power ramp up and down curves are controlled by altering the control or bias voltage applied to a power amplifier or a voltage controlled amplifier (VGA) modulator integrated circuit.
• VGA voltage controlled amplifier
• the controls to meet power control specification requirements, such as power versus time and transient adjacent channel power masks for GSM-FracN, WCDMA, and Cartesian IQ multiple access modes, are typically performed by a closed loop power control system.
• the slope of the control voltage versus transmit power output curve varies with respect to input power levels (dBm) at the power amplifier. Prediction of variations of the power input to the power amplifier and programming of corresponding system parameters is difficult. The slope of control voltage versus the transmit power output curve also changes with temperature and battery voltage variations.
• a transmit power control system which does not need extensive factory calibration of power control loop bandwidths over the power transition ranges, frequency bands of operation, temperature and supply voltage is desired.
• FIG. 1 illustrates a block diagram of a power control system according to an embodiment of the present disclosure.
• FIG. 2 illustrates a detailed block diagram of a portion of a power control system according to an embodiment of the present disclosure.
• FIG. 3 illustrates a transmit power vs. time plot for a closed-loop WCDMA system according to an embodiment of the present disclosure
• FIG. 4 illustrates a power vs. time mask curve and the switching transients during a transmit power ramp up and ramp down of a GSM burst according to an embodiment of the present disclosure.
• An adaptive transmit power control system which does not require extensive factory calibration of power control loop bandwidths over the power transition ranges, frequency bands of operation, temperature, and supply voltage is disclosed.
• the system automatically compensates for any gain or slope variations in the power control feedforward path as well as in the power detect feedback path to maintain system stability and meet desired performance specifications.
• the system includes an adaptive digital signal processing system architecture to accomplish this.
• FIG. 1 illustrates a block diagram of a power control system according to an embodiment of the present disclosure.
• Power control system 100 includes well known components such as a radio frequency (RF) transmitter 102, a coupler 104, an RF power detector 106, a programmable gain circuit 108, a detect filter 110, an analog to digital converter (ADC) 112, digital activity detection unit 114, reference ramp look up table 116 whose output is multiplied by the target final power level, loop filter 118, power control digital to analog converter (DAC) 120, reconstruction filter 122, analog gain control stage 124, and power amplifier 126.
• RF radio frequency
• ADC analog to digital converter
• DAC power control digital to analog converter
• reconstruction filter 122 analog gain control stage 124
• power amplifier 126 power amplifier
• Power control system 100 also includes an error squaring block 204, an adaptive filter coefficients calculation unit 128 and an N-tap adaptive filter 130.
• the number of the taps of adaptive filter 130 can be programmable. In operation, the coefficients of adaptive filter 130 are adjusted based on the difference between a reference ramp D and feedback signal A ⁇ .
• the N tap adaptive DSP system is configured to track any gain/slope variations in the analog feedforward and feedback paths of the power control system. It will be appreciated that the error squaring block 204 may be considered part of the filter coefficients calculation unit 128.
• FIG. 2 illustrates a more detailed block diagram of a portion of a power control system according to an embodiment of the present disclosure, n is the desired input signal,
• A is the signal that has to ideally track n irrespective of any gain/slope variations in k k the analog feedforward and feedback paths.
• E D - A.
• # C used to adjust the taps of adaptive filter 130 by employing an adaptive technique, such as a least mean square (LMS) adaptive algorithm.
• LMS least mean square
• the error signal E is then squared by square unit 204 and used to adapt the filter taps of adaptive filter 130 as illustrated in FIG. 2 and as described by the following equations.
• the output of adaptive filter 130, 5 E k w lk + E k _ 1 w 2k , is calculated.
• the initial weight vectors and the initial input vectors E 's are assumed to be zero.
• the convergence factor ⁇ determines the stability and the speed of convergence.
• the output of adaptive filter 130 feeds loop filter 118.
• loop bandwidths are set close to an optimal setting and the adaptive algorithm adjusts for any gain/slope variations with the control loop to meet power control specifications.
• Equations 1 to 5 summarize a specific embodiment of the adaptation process.'
• Both plots in Fig. 3 show a power up change from 15 dBm to 24dBm at the antenna. Both plots in this figure show the Power versus Time response for the on-channel signal as well as that at the adjacent channel (5 MHz offset), and alternate channel (10 MHz offset).
• the plot on the left shows these responses without using the proposed adaptive signal processing scheme whereas the one on the right shows these responses using the proposed adaptive signal processing scheme.
• the power control system fails to meet the 50 us required settling time for the on-channel power by employing a fixed loop bandwidth programmed in the loop filter without using the proposed adaptive signal processing technique.
• FIG. 4 illustrates the power versus time mask during a transmit power ramp up and ramp down of a GSM-FracN burst according to an embodiment of the present disclosure.
• the power control system compensates for the inappropriate settings of the loop bandwidths (-22 dB instead of -11 dB).
• the loop bandwidths do not need to be modified to a different value in order to meet the Power vs. Time Mask and the switching transient specifications.
• Simulations indicate that the adaptive algorithm according to an embodiment of the present disclosure can compensate for up to +/-11 dB variations in the closed loop system gain using a fixed convergence factor to meet the desired power versus time and transient power specifications.
• the algorithm converges nominally without causing any additional switching transients.
• the need for factory calibration of the closed loop parameters for each band and for each input power levels of the PA can be eliminated, thus saving time and money.
• power amplifier droop compensation circuits can be eliminated because the filter taps are adjusted sample by sample and track the reference ramp and thus compensate for any power amplifier droops in the analog RF transmit path.
• the closed loop system is more tolerant to gain variations in the feedforward and feedback paths, it provides a more stable and robust control system.
• the arbitrary analog gain control stage can be a baseband amplifier.
• the arbitrary analog gain control stage can be an RF amplifier where the RF amplifier is a voltage controlled amplifier or a power amplifier.
• a power control system comprising: a gain control stage configured to amplify an input signal to produce an amplified signal; a power detector coupled to an output of the gain control stage, the power detector to detect a ramp of the amplified signal and to provide an indication of the ramp; and a controller coupled to the power detector and the gain control stage, the controller configured to adjust a supply or control voltage to the gain control stage responsive to the indication of the ramp to cause the supply or control voltage to change as the ramp varies from a predetermined ramp, wherein the predetermined ramp comprises a desired waveform curve modified by a required power level.
• the power control system as recited in Claim 1, wherein the required power level comprises a mask according to a predefined power versus time specification and a transient power specification.
• the power control system as recited in Claim 5, wherein the operating conditions comprise a power input level to an amplifier stage, temperature, frequency band of operation, and a battery voltage level.
• the controller comprising: an error squaring unit; and an adaptive filter coefficients calculation unit; and an adaptive filter having multiple taps coupled to the adaptive filter coefficients calculation unit; wherein the ramp of the amplified signal is compared to the predetermined ramp producing an error term; herein the adaptive filter coefficients calculation unit uses the error term to calculate and adjust one or more of the multiple taps of the adaptive filter; wherein an output of the adaptive filter is fed into a loop filter that accumulates the output signal.
• the power control system as recited in Claim 7, further comprising: an activity detection circuit for producing an activity output indicating a detection of activity; wherein the activity output selects between a null signal when activity is not detected and the predetermined ramp when activity is detected to compare with the ramp of the amplified signal.
• an activity detection circuit for producing an activity output indicating a detection of activity; wherein the activity output selects between a null signal when activity is not detected and the predetermined ramp when activity is detected to compare with the ramp of the amplified signal.
• a voltage control circuit coupled between the controller and the gain control stage, wherein the controller produces a control signal responsive to the error term; the voltage control circuit processing the control signal to produce the supply voltage.
• the power control system as recited in Claim 1, further comprising: a loop filter coupled to the output of the controller for filtering an output of the controller using a fixed loop bandwidth, wherein the fixed loop bandwidth is independent of operating conditions, the operating conditions including variations of analog circuit elements over temperature, supply voltage, frequency band of operation.
• a method of amplifying a radio frequency (RF) signal comprising: amplifying the RF signal with a gain control stage to produce an amplified signal; detecting a ramp of the amplified signal; comparing the ramp of the amplified signal to a predetermined ramp producing an error difference, wherein the predetermined ramp comprises a desired waveform curve modified by a required power level; dynamically adjusting multiple taps of an adaptive filter based on the error difference signal producing a control signal; filtering the control signal with a loop filter that has a fixed loop bandwidth producing a filtered control signal; and controlling a control voltage of the gain control stage based on the filtered control signal.
• RF radio frequency
• the required power level comprises a power versus time mask and the desired waveform curve comprises a raised cosine wave. 19. The method, as recited in Claim 17, wherein the required power level comprises a mask according to a predefined power versus time specification and a transient power specification.

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• Transmitters (AREA)
• Amplifiers (AREA)
• Control Of Amplification And Gain Control (AREA)
• Mobile Radio Communication Systems (AREA)
• Feedback Control In General (AREA)

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• 2003
  • 2003-12-09 US US10/731,069 patent/US7215972B2/en not_active Expired - Fee Related
• 2004
  • 2004-11-04 WO PCT/US2004/037061 patent/WO2005060451A2/en not_active Ceased
  • 2004-11-04 CN CN200480033964A patent/CN100586207C/zh not_active Expired - Fee Related
  • 2004-11-04 JP JP2006543820A patent/JP4921976B2/ja not_active Expired - Fee Related
  • 2004-11-04 EP EP04810478.0A patent/EP1917714B1/en not_active Expired - Lifetime

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