AUTOMATIC GAIN CONTROL WITH TEMPERATURE COMPENSATION
FIELD OF THE INVENTION The present invention relates to an automatic gain control. More particularly, the present invention relates to adjusting the transmission power in a portable radio, which responds to the temperature. BACKGROUND OF THE INVENTION The Federal Communications Commission (FCC) regulates the use of the radio frequency (RF) spectrum. The FCC allocates certain bandwidths within the spectrum for specific uses. A user of an allocated bandwidth of the RF spectrum must take some measures to ensure that the radiated emissions inside and outside that bandwidth are kept within acceptable levels to avoid interference with other users operating in that bandwidth. or other bandwidths. These levels are governed both by the FCC and by the particular groups of users of said bandwidth. An 800 MHz cell phone system operates its forward link, ie the transmission of the cell to the radiotelephone, in the bandwidth of 869.01
P1531 / 97MX MHz at 893.97 MHz; and the reverse link, ie the transmission of the radiotelephone to the cell, in the bandwidth from 824.01 MHz to 848.97 MHz. The forward and reverse link bandwidths are divided into channels, each of which occupies a width of band of 30 kHz. A particular user of the cellular system can operate on one or more of these channels at the same time. All users of the system must ensure that they are complying with the permitted levels of radiated emissions inside and outside the channel or channels that have been assigned to them. There are different modulation techniques that can be used in the cellular radiotelephone system. Two examples of these modulation techniques are frequency division multiple access (FDMA) and code division multiple access (CDMA). The FDMA technique is used in the advanced mobile phone system (AMPS) which is described in more detail in the IS-54 standards document. The requirements for the CDMA radiotelephone system are described in more detail in the IS-95 standards document. The FDMA modulation technique generates signals that occupy one channel at a time, while the CDMA modulation technique generates signals that occupy several channels. Both techniques must control their reverse link radiated emissions within acceptable limits inside and outside the
P1531 / 97MX channel or assigned channels. For maximum system performance, users of the CDMA technique must carefully control the level of radiation power within the channels in which they are operating. Two methods to control the power of radiation are the control of power of open loop and of closed loop. Together, these two power control methods determine the reverse link transmission energy, as disclosed in U.S. Pat. No. 5,056,109 to Gilhousen et al. assigned to QUALCOMM, Incorporated. Figure 1 shows a typical cellular radiotelephone. Both a CDMA-based and a FDMA-based radiotelephone, there is the possibility of operating the power amplifier (101) in the transmitter beyond the point where the radiated emissions outside the channel are maintained in an acceptable manner. This is mainly due to the distorted output levels of the power amplifier (101) at high output powers. Also, operating the power amplifier (101) beyond a certain point can cause internal interference to the radio. For example, a disruptive discharge of a PA (power amplifier) in CDMA affects the phase noise of the synthesizer due to large current transitions. Both cases cause unacceptable performance
P1531 / 97MX of the radio. Maintaining the output power in the proper channel can be difficult due to some undesirable effects in the radiotelephone apparatus. For example, the radio with CDMA base must implement a power control system that operates on a very wide dynamic limit, 80dB to 90dB, in such a way that the transmitted output power is linearly related to the received input power. Linear and non-linear errors that occur both in the RF sections of the receiver (103) and the transmitter (102) can cause unacceptable performance in the power control. Also, both radios based on FDMA and CDMA must operate on different channels while maintaining acceptable levels of output power. The variation in the power output level and the detection of input power against the frequency can cause an unacceptable amount of error in the amount of power transmitted from the reverse link. Another problem with radio power control is the heat generated by power amplifiers and the supporting circuitry. The heat dissipation of these parts is related to the RF power output of the power amplifier. This heat dissipation can be managed with
P1531 / 97MX large heat sinks, fans and other mechanical devices that remove heat. However, in each case, additional weight and cost is added to the radio. In the case of the portable radio, adding a fan or a large heat sink is not feasible due to the need to reduce the size, weight and cost of the radios. These cases represent significant problems for the radio designer with both FDMA and CDMA bases. There is a need to reduce the operating temperature of a radio without adding substantial weight and cost.
SUMMARY OF THE INVENTION The automatic gain control with temperature compensation of the present invention encompasses a power amplifier apparatus with temperature compensation. This apparatus consists of a variable gain amplifier that has a control input to adjust the gain of the amplifier. A power detector is coupled to the variable gain amplifier and generates a power value of the transmitted signal. A temperature sensor is used to generate a temperature signal for certain predetermined heat generating components. A power control circuit has a first input coupled to the power detector, a second input coupled to the temperature sensor, and
P1531 / 97MX an output coupled to the control input of the variable gain amplifier. The power control circuitry adjusts the variable gain amplifier in response to the power value and the temperature signals.
BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 shows a block diagram of a frequency section of the radiotelephone of the prior art for use in a radiotelephone system. Figure 2 shows a block diagram of the power control correction instrumentation of the present invention. Figure 3 shows a block diagram of the power limit control section related to Figure 2. Figure 4 shows a block diagram of the closed loop power control section related to Figure 2. Figure 5 shows a block diagram of the threshold limit control section of the PA related to Figure 2. Figure 6 shows an alternative embodiment of the present invention employing a power limiting control system based on a control of
P1531 / 97MX accumulator feedback. Figure 7 shows an alternative embodiment of the present invention employing a power limiting control system based on a closed-loop power control accumulator. Figure 8 shows an alternative embodiment of the present invention employing a power limiting control system based on an integral feedback control. Figure 9 shows an alternative embodiment of the present invention that uses a power limiting control system based on a reception power measurement and the closed loop power control setting to calculate the output power. Figure 10 shows a block diagram of the automatic gain control with temperature compensation of the present invention. Figure 11 shows a graph indicating the benefits of the modality of Figure 10.
DETAILED DESCRIPTION OF THE INVENTION The process of the present invention provides a correction of the power control for a mobile radio as well as the maintenance of maximum levels of acceptable emission of input and of band output. This takes
P1531 / 97MX performed by a real-time compensation that uses a set of correction tables that are generated during the production test of each radio. Figure 2 shows a block diagram of the CDMA radius with the instrumentation of the power control correction of the present invention. The figures. 3, 4 and 5 detail the specific blocks of Figure 2. The radius consists of a linearization section of reception, transmission linearization section, polarized control section of the power amplifier, and a power limit control section. The reception linearization section includes an automatic gain control section (AGC). The input signal to the AGC section is received at the forward link and amplified by a low noise amplifier (211) (LNA). The output of the LNA (211) enters a variable gain amplifier (212). The variable gain amplifier (212) produces a signal that is converted into a digital signal using an analog-to-digital converter (ADC) (213). The power of the received digital signal is then recorded by a power detector (214). The detector
(214) of power includes an integrator that integrates the detected power with respect to a reference voltage. In the preferred embodiment, this reference voltage is
P1531 / 97MX provided by the radio demodulator to indicate the nominal value at which the demodulator requires the loop to be closed in order to maintain the constant power level. The demodulator requires this value for optimal performance since the power level too far from the optimum limit will devalue the performance of the demodulator. The power detector (214) executes the integration, thereby generating an AGC set point. The set point and a reception frequency index are entered into a reception linearization table (216). The AGC setpoint and the frequency index are used to direct the linearizer (216), thereby allowing access of the appropriate calibration value. This calibration value is output to a digital-to-analog converter (215) that generates the analog representation of the reception AGC setting. The analog value adjusts the polarization of the variable gain amplifier (212). The control of the variable gain amplifier (212) forces the receiving AGC loop to close, such that the input of the receive linearization table (216) follows a predetermined straight line with respect to the RF power of the receiver. entry. This linearization removes unwanted linear and non-linear errors, in addition to the
P1S31 / 97MX variations against frequency that would otherwise be apparent at the input of the receiver linearization table (216) at the receiver. These errors and variations will contribute to errors in the transmitter. In order to reduce the error in the reception and transmission chains against the frequency, the linearizations of reception and transmission use the frequency index that specifies the central frequency of current in which the reception and transmission chains are operating. During the manufacturing calibration of the radio, linearizers are loaded with values, in addition to the aforementioned calibration values that are linked by frequency to correct the errors related to the central operating frequency. The AGC setpoint is the open loop power control signal for the radio. In the preferred embodiment, this is the power control executed by the radio itself without control input from the cells. As the power of the signal received from the cell increases, the radius decreases its transmission power. This output power control is carried out by means of the AGC set point which is filtered by a low pass filter (217). The transmission section includes an adder
Digital P1531 / 97MX (210) that combines the AGC set point and the closed loop power control setting (206). The output of the adder (210) is fed into a section
(205) of power control limit. The operation of the power control limit section (205) and the section
(206) Closed-loop power control, illustrated in the Figures. 3 and 4 respectively, will be explained later in greater detail. The output of the power control limit section (205), together with the transmission frequency index, are used to direct the values stored in a transmitter linearization table (204). The transmitter linearization table (204) contains values determined by the radio production tests. The selected value is input to the digital-to-analog converter (203), whose output, which is an analog representation of the digital input value, controls the variable gain amplifier (202). The polarization of the variable gain amplifier (202) is adjusted by the analog calibration value to a point at which the input to the table
(204) Transmitter linearization follows a predetermined straight line with respect to the output RF power.
This linearization removes the unwanted linear and non-linear errors along with the variations against
P1531 / 97MX frequency in the transmitter. This, combined with the aforementioned reception linearization, largely reduces the errors of closed loop and open loop power control due to RF performance imperfections. The polarization control section (218) of the power amplifier (PA) controls the polarized point of the transmission PA (210) based on the transmission gain setting, such that the transmission sidebands for the gain adjustment given are optimized against the current consumption of the PA (201). This allows a phone with battery power to maximize the talk time by reducing the PA current draw (201) at lower output powers, while maintaining the levels of the sidebands at higher levels of power. departure. The power control limiting section (205) is illustrated in Figure 3. The power control limiting section (205) controls the closed loop power control and the transmission gain settings when the adder output (210) Transmission gain corresponds to a level of output transmission power, which is equal to or greater than the maximum output power desired. The maximum gain setting is determined by the control section (209) of
P1531 / 97 X PA limit threshold. The threshold control section (209) determines the maximum gain setting based on a nominal value that is modified by a real time measurement of the transmitted output power. The measurement is carried out by the analog power detector (207) whose output is transformed into a digital signal by means of the analog-to-digital converter (208). Then, the digital power value is input to the threshold control section (209). The threshold control section, detailed in Figure 5, operates by means of the linearizer (501) of the high power detector (HDET), graduating The digital value of input power in order to match the numerology of the digital transmission gain control section. The scalded output from the linearizer (501) is subtracted (502) from the nominal maximum gain setting. The maximum gain setting can be coded into a hard element within the radius during assembly or can be entered during fabrication and radio testing. Subsequently, the difference of the maximum gain setting and the scaled output power, by means of the adder (503), is added to the maximum gain setting. The sum of these signals is then used as the adjustment
P1531 / 97MX corrected for maximum gain. This real-time modification of the perceived power helps mitigate the errors introduced by the temperature variations and the age of the PA transmitter. In other words, if the difference between the maximum gain setting and the power value measured in real time is 0, then the correction is not needed. If there is a difference between the two, the difference is used to correct the maximum gain setting. With reference to Figure 3, a digital comparator (301) detects the moment when the output of the adder
(210) Transmission gain equals or exceeds the maximum gain setting. The comparator (301) controls a 2: 1 multiplexer (302) that extracts the maximum allowed setting when the output of the adder (210) exceeds the maximum allowed setting. When the output of the adder (210) is less than the maximum allowed setting, the multiplexer (302) extracts the direct output of the adder (210). This prevents the transmitter from exceeding its maximum operating point. The closed loop power control section (206), illustrated in Figure 4, accumulates the power control commands sent on the forward link by the radio control cellular site and outputs a gain adjustment signal. The power control controls are grouped in an accumulator (401). The operation
P1531 / 97MX of the accumulator (401) is controlled by the power control limiting section (205) when the transmission PA (201) is extracting the maximum allowed power. When the output of the adder (210) changes from being less than the maximum allowable setting to be equal to or greater than this, the output of the closed-loop power control accumulator (401) is ensured inside a jogger (402). While the output of the adder (210) is equal to or greater than the maximum allowable setting, as determined by the comparator (403) and the gate circuit (404) NAND, a gate (405) AND unmasks any control command of closed loop power that would force the accumulator (401) to remain on the hooked value of the tilters (402). This prevents the accumulator from becoming saturated during the power limitation even though it allows the closed-loop power control setting to change to any level below the engaged value. An alternative embodiment of the process of the present invention is illustrated in Figure 6. In this embodiment, a power limiting control system is used based on an accumulator feedback control. The system operates first by measuring the output power PA (609) using a power detector (610). The detected power is then converted into digital by
P1531 / 97MX means an ADC (611) and is compared to a maximum setting allowed by the comparator (601). If the output power is greater than the maximum setting, the power limiting accumulator (602) begins to turn off the power by reducing the gain of the variable gain amplifier (608). If the output power is less than the maximum setting, the power limiting accumulator (602) returns to the correction value 0 dB. In this embodiment, a closed-loop power control limiting function (604 and 605) similar to that of the preferred embodiment is used. However, the actuator for the closed loop power control limiting function is a comparator (603) which detects when a power limiting accumulator (602) is limiting the output power, by comparing the output of the accumulator (602) to 0 dB with the comparator (603). The linearization compensation tables, similar to the tables of the preferred embodiment, are added to the transmission gain control using an adder (606). In another alternative modality, illustrated in
Figure 7, a power limiting control system is used which is based on the closed-loop power control accumulator (702). The system operates first, by measuring the output power PA (705) using a power detector (706). The detected power becomes
P1531 / 97MX digital (707) and compared to a maximum setting allowed by the comparator (701). If the output power is greater than the maximum setting, the closed-loop power control accumulator (702) is modified to turn off the power of the amplifier (704) by one step every 1.25 ms until the output power is less than the maximum setting. If the output power is less than the maximum setting, the closed-loop power control accumulator is not modified. The linearization compensation tables, similar to the preferred embodiment, are added within a transmission gain control using an adder (703). In yet another embodiment, illustrated in Figure 8, a power limiting control system is used that is based on integral feedback control. The system operates first by measuring the output power PA (808) using a detector (809). The detected power becomes digital (810) and is introduced to an integrator (801) that follows the equation: -. f (set point - detected) dt K The integrator (801), which generates a gain control signal, is saturated at 0 dB and -63 dB correction. The gain control signal is thus limited within a range. If the power of
P1531 / 97MX output is greater than the set point, the integrator shuts off the power output of the amplifier (807) at a speed based on the constant K of integration, until the set point is reached. The integrator is allowed to turn off the power up to 63 dB. If the output power is less than the set point, the output of the integrator (801) will be forced to be zero, therefore not adjusting the output power. In this embodiment, a closed-loop power control limiting function (803 and 804) similar to that of the preferred embodiment is employed. However, the actuator for the closed loop power limiting function is a comparator (802) which detects when the power limiting integrator (801) is limiting the output power. The linearization compensation tables, similar to those of the preferred embodiment, are added within the transmission gain control using an adder (805). In another embodiment, illustrated in Figure 9, a power limiting control system is used that is based solely on a reception power measurement, as determined by the power query table (902) Rx, and the adjustment of Closed-loop power control opposite the actual actual output power. The limiting function of transmission power and function
P1531 / 97MX (901) closed-loop power control limiter can be used with one or other modality using the saturation accumulator (903) or any of the alternative modes. However, only the reception power and the closed-loop power control setting are used to calculate the transmission output power. Most of the heat generated by the radio comes from the PA and the DC regulator that supports the PA. This generated heat, higher than the ambient temperature, can exceed the temperature capacity of many of the radio components. The preferred embodiment of the present invention, which is illustrated in Figure 10, controls the transmit power based on temperature. This mode uses temperature sensors such as thermistors, placed near the heat sensitive components or near the components that generate most of the radium heat, PA and the DC regulator. The output power PA is adjusted based on the temperature of these components. This can be achieved by adjusting the maximum gain adjustment signal created by the threshold limit control (209) PA in Figure 2, included in the block (1020) power detector of Figure 10. This allows the power maximum transmission output of
P1531 / 97MX radio is adjusted up or down based on the measured temperature. The level of transmission power is recorded so that it is not reduced below these levels required by IS-95 or IS-54 standards. Referring to Figure 10, the transmission AGC (1035) is coupled to the transmission PA (1015). The regulator (1010) DC regulates the DC power to the PA (1015). A power detector (1020) determines the power of the signal transmitted by the PA (1015) and feeds that information to the power control circuitry (1030). The power detection can be executed as described in the embodiment of Figure 2. The power control circuitry (1030) uses the temperature sensed by the temperature sensors (1025) together with the detected transmission power to adjust the gain of the AGC transmission through a control input. The power control circuitry (1030) can be implemented in various ways. A method generates a control signal that is proportional to the amount of transmission power adjustment required for a measured temperature. The control signal is added within the transmission gain control section of the radio detailed in Figure 2, to reduce the output transmission power, thereby reducing the temperature. This generation of the signal
P1531 / 97MX and its sum can be executed either by digital circuitry or analog circuitry or by either, using the continuous or sampled versions of the required signals. Other modes adjust the output power based on a measured temperature and transmit the output power when adjusting a stepped gain block, such as a switching attenuator in the transmission chain. This gain block can be placed in different locations in the chain. Additionally, the output power could be adjusted by varying the polarized DC point or the main DC supply voltage of PA. While Figure 10 shows the AGC (1035) and the PA (1015) as if they were separate, other modalities use a variable gain PA. The variable gain PA has a gain control input, coupled to the power control circuitry (1030) and controlled in the same manner as the previous mode. The power adjustment executed by the modality of Figure 10, will not cause problems with the CDMA, IS-95 specification or with the AMPS, IS-54 specification. The IS-54 specification relaxes the transmission power output requirements at high ambient temperatures. While the IS-54 does not specifically relax the power output requirements,
P1S31 / 97MX allows a variation of + 2 dB and - 4 dB in the transmission power of any given power level. Part of this limitation can be used to reduce the level of transmission power at high ambient temperatures. The benefits of the modality of Figure 10 are illustrated in Figure 11. This graph shows that without the temperature setting, the internal temperature of the radius continues to increase as the ambient temperature increases. With the temperature setting of the present invention, the internal temperature of the radius starts to lower the level after it reaches a predetermined ambient temperature. In summary, the process of the present invention ensures that the transmission sidebands and the noise of the phase synthesizer of a radio transmitter remain within a predetermined specification by limiting its maximum output power. This power limitation is achieved by a control loop that includes a calibration look-up table. Therefore, a radius using the process of the present invention, will not exceed its maximum nominal power level due to the cell having too many power ignition controls. The radius limits the output power even when the cell erroneously decides that the radius power should increase. P1531 / 97MX