MXPA01001341A - Automatic gain control circuit for controlling multiple variable gain amplifier stages while estimating received signal power - Google Patents

Abstract

The present invention is a novel and improved AGC circuit which is generically configurable to accommodate a variety of AGC amplifier configurations to enhance IP3 performance and reduce required amplifier current, while providing a received power estimate which remains valid regardless of how the gain or attenuation is distributed among the various amplifiers. A generic control circuit maintains this power estimate in a single overall gain amplification value by distributing gain to at least two amplifier stages in response to that value. By programming or hard coding a few key parameters, a generic control circuit can control a wide variety of amplifier configurations.

Description

AUTOMATIC GAIN CONTROL CIRCUIT FOR CONTROLLING MULTIPLE VARIABLE STAGES OF AMPLIFIER OF GAIN IN SO THAT THE RECEIVED POWER OF THE SIGNAL IS ESTIMATED BACKGROUND OF THE INVENTION I. Field of the invention The present invention relates to automatic gain control circuits. More particularly, the present invention relates to a novel and improved automatic gain control circuit capable of independently controlling multiple stages of variable gain amplifier while maintaining an estimate of the power of the received signal.

II. Description of the Related Art In modern communication systems, it is common for a receiver to contain automatic gain control (AGC) circuitry for amplifying or attenuating the received signals at a desired level of reference for further processing by the receiver. An exemplary AGC circuit is described in U.S. Patent No. 5,099,204 entitled "LINEAR GAIN CONTROL AMPLIFIER", assigned to the assignee of the present invention and incorporated herein by reference. In U.S. Patent No. 4,901,307, entitled "SPREAD MULTIPLE ACCESS COMMUNICATION SYSTEM USING SATELLITE OR TERRESTRIAL REPEATERS", a communication system using these AGC circuits is described, this patent is assigned to the assignee of the present invention. and incorporated herein by reference. An earlier system is also described by the Interim EIA / TIA IS-95 Standard, entitled "Mobile Station-Base Station System" (subsequently IS-95), incorporated herein by reference. A mobile station in an IS-95 system, in addition to requiring incoming signals to be controlled in gain for further processing, must ensure that their transmitted signals are hermetically controlled in order not to interfere with other mobile stations in the system. This power control scheme is described in U.S. Patent No. 5,056,109, entitled "METHOD AND APPARATUS FOR CONTROLLING TRANSMISSION POWER IN A CDMA CELLULAR MOBILES TELEPHONE SYSTEM", assigned to the assignee of the present invention and incorporated herein by reference. reference. An element in this power control scheme is the use of a measurement of the received signal power, and thus in contrast in systems where the only requirement of an AGC circuit is to provide incoming signals at the appropriate reference level, An AGC circuit of IS-95 must allow the calculation of the received signal strength. Ideally, you could build amplifiers that are perfectly linear, at least over the same interval. Then, the amplifier is characterized by the equation f (x) = ix, where f (x) is the output, x is the input and ki is the gain of the amplifier. Actually, the amplifiers are not perfectly linear, and this non-linearity introduces distortion in the signal that is amplified. Of all possible volta is input, an amplifier has what is called its "linear" interval and its "non-linear" interval. The linear range is where the amplifier comes closest to a linear amplifier. The introduced distortion can be approximated to a third order component. A more realistic characterization of an amplifier is given by the equation f (x) = ktx + k3x3. Here k3 is the gain of the third order component. An amplifier with a smaller value for k3 will be more linear than an amplifier with a higher value. One type of distortion introduced by non-linear amplifiers that is particularly problematic comes from the intermodulation terms of two frequencies that are outside the band of interest for a mobile station. An example of this can be seen when deploying an IS-95 system in close proximity to a narrowband system such as AMPS or GSM. The performance of an amplifier with respect to intermodulation is given by its IP3 point. For calculation purposes, it is assumed that the transmitters of the desired band and the source of the unwanted frequencies are co-located. This means that as the mobile station moves towards the transmitter, both receive the desired power and increase the intermodulation power. Point IP3 is the point where the third order intermodulation power of the two equal power tones, decompensated in frequency, is equal to the term of the first desired order. To optimize the IP3 performance of an amplifier, the third order gain, k3, must be reduced to the minimum. One way to increase the performance of IP3 is to increase the "linear" range of the amplifier. The supply of more current to the amplifier can do this. However, in typical mobile communication systems, the power in a mobile station is at a high price and the current increase is only done when absolutely necessary. The reduced consumption of energy or power translates into an increased waiting time and speech in a mobile station, or alternatively in a reduced battery requirement that leads to smaller and lighter mobile stations. An alternative to increasing the linear range is to reduce the amplitude of the incoming signal so that it is within the existing linear range of the amplifier. The IS-95 specifies a minimum level of what it describes as an intermodular rejection. Figure 1 shows a graph of the typical intermodular rejection ratio. For a given range of received power, the receiver must be capable of * 1 Ii tolerate a certain amount of interference, get a certain ratio of intermodular rejection (IMR), as shown by the "speculation" marked, linear between the points SI and S2 of specification. The intermodular rejection of an amplifier with fixed IP3 will increase 1/3 of a dB for each dB increase in received input power. The tilt of the speculation line may not be 1/3 of a dB per dB, and it is not actually in IS-95. The slope of IS-95 is approximately 1 dB per dB slope. For a speculation as shown, an amplifier must satisfy the specification at point S2. This will produce an IMR given by Al line. To meet the specification requirement in the SI point, an amplifier of Less current could be used which will produce an IMR given by A2. As shown, the amplifier that meets point S2 is over-designed for the SI point. This overdesign can be equal to an increase in polarization current resulting in a reduced battery life, or requiring more expensive components, or both. Figure 2 shows an AGC design that could exhibit the properties attributed to the Al or A2 lines. The signals received on the antenna 100 are directed to the ultra low frequency (UHF) low noise amplifier (LNA) 110. A dashed arrow is shown through the amplifier 110 to indicate the option of having to be a variable gain amplifier. This variable gain configuration will be discussed later. The received signal is amplified by LNA 110 and down-converted to mixer 115 via the UHF frequency generated by local oscillator 120 of UHF. The downconverted signal is passed through a bandpass filter 130 and amplified by the intermediate frequency (IF) variable gain amplifier 140. This amplified IF signal is then converted down to the mixer 145 via an IF frequency generated by the IF frequency generator 150. The received signal is now in the baseband, and the signal 160 of the received signal strength (RSSI) generates an estimate of the power of the received signal. The difference of this estimate and a reference power stored in the power reference 165 is calculated in the adder 170, and the AGC 180 of RX acts on this error difference to produce the appropriate AGC_VALUE 195. The AGC_VALUE 195 is fed through a linearizer 190 to the variable gain amplifier 140. The linearizer 190 compensates for any non-linear dB / V characteristic of the variable gain amplifier 140. Linearization is described in U.S. Patent No. 5,627,857, entitled "LINEARIZED DIGITAL AUTOMATIC GAIN CONTROL", assigned '10 to the assignee of the present invention and incorporated herein by reference. The AGC 180 of RX may be a variety of circuits as is known in the art that alter the AGC_VALUE to drive the calculated difference in the adder 170 so close from scratch as possible. Once this circuit converges, the baseband signal of the mixer 145 is at the appropriate input power level and can be demodulated (in a circuitry not shown). Typically, the downward conversion of IF is performs on phase and quadrature components of the signal and additional filtering is performed, but these are not shown for reasons of clarity. The circuit as described above will display the IMR response of the Al line in Figure 1 when is designed at a fixed current level. It is pointed out that AGC_VALUE can be used to estimate the received power, but only after factoring in the gain from the complete reception chain. One way to reduce current overload is to use a lower current amplifier that will require the Al line to be generated and introduce variability in the front end gain gate, LNA 110, as shown by the dashed arrow of Figure 2. As an example, it is assumed that this is a fixed gain switched LNA, meaning that it is either with a fixed gain or is derived jointly. When the LNA 110 is switched, the amplification will be reduced, or it will be added to attenuation. This reduces the linear range requirement for the IF amplifier 140. When the LNA stage is switched, a performance cost is paid through an increased floor of noise. The carrier-to-interference (C / I) figure is approximated to this thermal noise floor from the amplifier circuits plus the inter-module components plus the co-channel interference. The demodulator performance is a C / I baseband function. As the received power (C) increases, the total interference may increase. Since the noise floor remains approximately constant if no LNA switching is performed, the excess margin can be negotiated for improved IP3 performance when the amplifier is switched which results in an improved IP3 performance at the cost of an floor increased noise. Figure 3 shows an IMR speculation that is the same as shown in Figure 1. However, the variable gain LNA IMR described above is completely different from the IM or A1 lines of IMR. The amplifier must have a linear range and the current consumption to support the IMR given by linear segment Rl. This is less current that the amplifier needs to supply in the line Al of Figure 1. As the input power is increased, the linear range of this amplifier is used and without further fall below the point S3 of speculation. In contrast, the attenuation is added when switching LNA 110 and therefore, the inputs to the amplifier IF 140 are returned within their linear range and the performance of IP3 amounts, in this example, to performance comparable to the amplifier required to produce the line Al. This is shown by line segment R2. In a similar way, if a truly variable gain LNA 110 is used, instead of the simple on / off example demonstrated so far, the performance of the AGC amplifier chain can be made very close to the speculation itself required, and therefore the minimum power consumption required.

The total gain value in the amplifier chain in the AGC can be used as a measure of the total received power. This is because the basic function of an AGC is to take an input power level and reduce it to a reference power level by applying a gain factor. If the gain factor is known, then the actual received power is also known since the reference power is known. However, for improved performance of IP3, it is desirable to be able to change the attenuation or gain distribution throughout the amplifiers in the AGC chain. But it is pointed out that once the profit is distributed among the stages, the AGC_VALUE 195 is no longer a good estimate. As shown above, a distribution of gain across a variety of amplifiers does not necessarily automatically produce a full AGC gain value which can be used as an estimate of received power (therefore for an estimate of transmission power). There is a need in the art for an AGC circuit that is controllable to improve the performance of IP3 as long as it produces a B useful estimate of the received power.

SUMMARY OF THE INVENTION The present invention is a new and improved AGC circuit that can be configured in a generic manner to adjust a variety of AGC amplifier configurations to improve the performance of IP3 and reduce the required amplifier current, while providing an estimate of received power that remains valid regardless of how the gain or attenuation is distributed among the various amplifiers. A generic control circuit maintains this power estimate at a full and individual gain gain value by distributing the gain at least two amplifier stages in response to that value. By programming or hard coding a few key parameters, a generic control circuit can control a wide variety of amplifier configurations. Among the provided configurations are switched LNA, and variable gain LNA, switched, variable gain and an uncoupled IF and a UHF variable gain LNA configuration. The invention may be extended to include multi-stage amplifier configurations. Although the preferred embodiment includes two stages, one can easily be adapted for UHF, one for IF, three or more stages. Various filtering schemes can be applied when estimating the power to adjust the temporal dynamics of the gain switching. For example, a low pass filter can be applied to the front end of UHF to give it a slower response than the IF stage. All these configurations and any subset can be supported in a generic single device.

BRIEF DESCRIPTION OF THE FIGURES The features, objects and advantages of the present invention will become more readily apparent from the detailed description set forth below when taken in conjunction with the drawings in which similar reference characters are identified accordingly all along and where: Figure 1 is a typical graph of intermodular rejection ratio; Figure 2 is an AGC circuit of the prior art; Figure 3 is a graph of the intermodular rejection ratio in conjunction with a switched LNA AGC configuration; Figure 4A is a switched / stepped LNA gain configuration; Figure 4B is a variable LNA gain configuration; Figure 4C is a switched variable attenuator; Figure 5 shows the preferred embodiment of the present invention; Figure 6 details the generic gain control circuit of the present invention; Figure 7A shows the generic gain control circuit configured for use with a switched LNA; Figure 7B shows an example static UHF / IF attenuation transfer function corresponding to the configuration shown in Figure 7A; '10 Figure 8A shows the generic gain control circuit configured for use with a variable gain attenuator, switched; Figure 8B shows the static transfer functions of UHF / IF attenuation of example corresponding to the configuration shown in Figure 8A; Figure 9A shows the generic gain control circuit configured for use with a non-switched variable gain LNA; Figure 9B shows an example static UHF / IF attenuation transfer function corresponding to the configuration shown in Figure 9A; Figure 10A shows the generic gain control circuit 7 configured for use with a non-switched variaole gain LNA in an alternate decoupled IF / UHF gain configuration; and Figure 10B shows an example static UHF / IF attenuation transfer function corresponding to the configuration shown in Figure 10A.

DETAILED DESCRIPTION OF THE PREFERRED MODALITIES The present invention provides generic AGC control for a variety of configurations. Figures 4A-4C show conceptually the various types of amplifier configurations that are supported in the invention. These are shown only as examples. Figure 4A shows a switched / stepped LNA gain configuration, which is conceptually the same as a LNA lead. The switch 305, under control of the LNA_RANGE signal, selects between the incoming signal and the incoming signal that has been attenuated through the link 300. The switched signal passes through the LNA 310, the UHF mixer 315, and up to the amplifier 320 of IF variable gain control. The IF amplifier 320 selects its gain value under the control of signal RX_AGC_ADJ. The amplified signal is then converted down to the baseband through the IF mixer 325. In practice, the attenuation through the chaining 300 can be performed through the derivation of LNA 310 instead of the attenuation of the signal. This is equivalent to the derivation of one or more stages of a multistage LNA. Figure 4B shows a variable gain LNA configuration. It differs from Figure 4A and only at the front end. Instead of switching a fixed attenuation on or off, under the control of the LNA_RANGE signal, the link 300, switch 305 and LNA 310 are replaced by the variable gain LNA 330 which sets its gain according to the signal LNA_GAIN. Figure 4C shows a variable attenuator, switched. Again, it differs only from Figure 4A and Figure 4B at the front end. Like Figure 4A, this circuit connects or disconnects the attenuation through the switch 305 under the control of the LNA_RANGE signal. However, the variable attenuator 330 under the control of the LNA_GAIN signal provides the attenuation. Figure 5 shows a preferred embodiment of the present invention. It is similar to the circuit shown in Figure 1, but it has important difference numbers. The generic gain control circuit 200 is inserted before the linearizer 190 of RX, and takes the AGC_VALUE 195 as an input. The generic gain control circuit 200, more fully described later, provides control to the UHF LNA 110 and the IF variable gain amplifier 140.

It also operates in conjunction with the optional linearizer 190 and the optional LNA linearizer 210 (which is another in addition to Figure 1). As shown, the UHF LNA 110 is of variable gain, but is optional. All of the conceptual modes described in Figures 4A-4C can be configured and controlled by the generic gain control circuit 200. The UHF LNA 110, if it is of variable gain, is controlled in gain by the LNA_GAIN signal through the linearizer FLO of LNA (if a linearizer is needed). If a switchable LNA configuration is being used, the IF LNA 110 is connected or disconnected via the LNA_RANGE signal. If the variable gain amplifier 140 is controlled by the signal RX_AGC_ADJ through the linearizer 190 of RX (if a linearizer is needed). It is noted that all amplifiers are controlled by the generic gain control circuit 200 based on the AGC_VALUE 195 signal. As such, despite the distribution of gains to the various amplifiers in any of the supported configurations, AGC_VALUE specifies the gain of the entire chain of amplifiers and as described above, can be used as a measure of the power received. This measurement can be used as a power reference in a transmitter (not shown). Although this circuit will work with all the necessary hard coded parameters, in the example mode it is deployed with the microprocessor 220 to control the circuitry and to receive feedback from it. The microprocessor 220 is used to configure the generic gain control circuit 200 and can provide linearized values to the linearizers 210 and 190, if linearizers are needed. In Figure 6 the generic gain control circuit 200 is detailed. The signal AGC_VALUE representing the gain of the entire chain of amplifiers is fed to the adder 250. Any gain that is distributed to other stages of the amplifier chain is subtracted from AGC_VALUE, and the rest is used as the gain factor RX_AGC_ADJ. Despite the actual gain distribution, the AGC_VALUE signal remains as a valid estimate of the received signal power, useful for tasks such as transmission power control. In normal operation, the stepper gain control 300 and the linear gain control 310 act on the AGC_VALUE. However, multiplexers 370 and 380 are part of an optional configuration whereby a filtered version with low pass AGC_VALUE, created by the LPF 360 depower RX, are used in place of the AGC_VALUE. The signal LNA_RANGE_FILT_SEL is used to control the selection of the filtered or unfiltered signal, AGC_VALUE, through the multiplexer 370. The signal LNA_GAIN_FILT_SEL is used to control the selection of the filtered or unfiltered signal AGC_VALUE through the multiplexer 380. When selects the AGC_VALUE filtered with low pass, then the AGC is mainly IF (fast circuit) with a slow external circuit that adjusts the UHF gain based on a long term estimate of the power of RX. A slower adjustment of the UHF gain is desirable to maintain the intermodular rejection between band fades. It is noted that due to the design union in this control scheme, in spite of whether a filtered AGC_VALUE or the initial AGC_VALUE is used in linear step gain control blocks 300 or 310 (or any number of additional gain stages) or distribution and profit schemes that can be used) a residual gain is always provided through RX_AGC_ADJ. Therefore, the total gain is always equal to the instantaneous value of AGC_VALUE. For clarity, in the following analysis, the filter option is not discussed, but it can also be included without loss of generality. The linear gain control 310 acts on AGC_VALUE to produce the LNA_GAIN signal. It is configured through two settings, LNA GAIN MIN and LNA_GAIN_RANGE. As shown, when the power of RX, which is the input to the linear gain control 310 from the multiplexer 380, is less than (4), LNA_GAIN_MIN, then LNA_GAIN will be zero. As the power of RX is increased beyond (4), the output increases with a slope of 1, providing an increase of dB per dB, until LNA_GAIN reaches the level programmed by (5), LNA_GAIN_RANGE. LNA_GAIN is used to control a variable gain LNA, displayed as UHF LNA 110 in Figure 5. It is noted that linearizer tables can be continued to provide other dB ramps per dB in real gain if desired. This optional feature will be discussed later in this. The LNA_GAIN is fed into the multiplexer 320, where it will be passed to an adder 330 unless it is zero as programmed with the signal LNA_LIN_SEL. The gain control 300 per step acts on the AGC_VALUE to provide a LNA_DECISION selector signal to the multiplexer 340 and the LNA_OFFSET value to the adder 330, where it is added to the multiplexer value 320. The step gain control 300 is programmed via LNA_FALL, LNA_RISE and LNA_OFFSET. As shown, when the power of RX, which is the input to gain control 300 per step of multiplexer 370, is less than (2), LNA_RISE, then the output of this block will be zero.

As the power of RX beyond (2) increases, the output is scaled to the value programmed by (3), LNA_OFFSET. LNA_DECISION is then activated to select the value of the adder 330 instead of the value zero. The output will remain at the step value (3), LNA_OFFSET, until the RX power falls below (1), LNA_FALL. If this occurs, the output will be reset back to zero and LNA_DECISION will be disabled. The independent control of (1) and (2) allows the hysteresis to be programmed so that an amplifier is not excessively commuted at an individual threshold trigger point. LNA_DECISION is used to provide LNA_RANGE, a control signal to activate the switched LNA that has been deployed as UHF LNA 100 in Figure 5. LNA_RANGE can be slightly altered from LNA_DECISION. For example, delay may be added to coordinate with the characteristics of the amplifier. LNA_DECISION can alternatively be controlled by a microprocessor to handle the control of LNA 110 of UHF. The output of the multiplexer 340 represents the gain that has been distributed to the UHF stage amplifier. It is subtracted from AGC_VALUE in adder 350 and the rest is. used as a gain value for the IF stage amplifier. It is clear to one skilled in the art that this solution can be extended and modified without changing the basic structure such that the AGC_VALUE is used to close the AGC circuit and provide an estimate of the received power as the real gain 5 is distributed among a variety of amplifiers. You can control more than two amplifier stages and your winnings will be added and subtracted in the manner shown above. Similarly, the alternative filtering schemes of AGC_VALUE could be used, and the invention is thought to provide the desired characteristics. Figure 7A shows the generic gain control circuit 200 configured to perform the control of the switched LNA, as shows conceptually in Figure 4A. This configuration will be useful with a switchable individual gain IF LNA 110 (shown in Figure 5). In this configuration, the output of LNA_GAIN is not used. LNA_LIN_SEL is used to select zero to be added to the adder 330. Similarly, the LNA_GAIN_RANGE could always be adjusted to provide zero at the LNA_GAIN output. LNA_OFFSET, (3), is programmed to match the gain provided by the UHF LNA. How I know described above, the UHF LNA is switched on and off according to the power of RX and the parameters LNA_FALL, (1), and LNA_RISE, (2). An example of the resulting attenuation for each of the IF and UHF gain stages is plotted in Figure 7B. It is noted that the sum of the IF and UHF gains is equal to the AGC_VALUE input, as expected. Figure 8A shows the generic gain control circuit 200 configured to perform the switched variable gain LNA control, as conceptually shown in Figure 4C. This configuration would be useful as an LNA F10 110 variable gain IF, switchable (shown in Figure 5). LNA_LIN_SEL is used to select LNA_GAIN that will be added to the adder 330. It is programmed as described above LNA_GAIN_MIN, (4), and LNA_GAIN_RANGE, (5), and is adjusted by consequently LNA_GAIN. LNA_OFFSET, (3) is programmed to correspond to the gain provided by the UHF LNA. As described above, the UHF flB LNA is connected and disconnected according to the power of RX and the parameters LNA_FALL, (1) and LNA_RISE, (2). Two examples of the resulting attenuation for each of the IF and UHF gain stages are plotted in Figure 8B. The two examples highlight the difference in behavior based on the relative positions of (2) and (4). In the example (a), the LNA is turned on before any linear gain term is added. In Example (b), the linear term has increased above zero before the LNA actually connects. It is noted that the sum of the IF and UHF gains is still equal to the input AGC_VALUE, as expected. Figure 9A shows the generic gain control circuit 200 configured to perform the variable gain LNA control, as conceptually shown in Figure 4B. This configuration will be useful with an unchanged variable gain IF LNA 110 (shown in Figure 5). This configuration, the output of LNA_RANGE is not used. LNA_DECISION is overconverted to activate the multiplexer 340 to select the output of the adder 330. Alternatively, LNA_RISE, (2) and LNA_ALL (1) can be programmed such that LNA_DECISION is always on. LNA_LIN_SEL is used to select LNA_GAIN to be added to the adder 330. The output of the step gain control 300 must be set to zero, which can be achieved by programming (3), LNA_OFFSET, to zero, or alternatively by programming (1; and (2) such that the output is never on. LNA_GAIN_MIN, (4), and LNA_GAIN__RANGE, (5) are programmed as described above, and LNA_GAIN is adjusted accordingly. An example of the resulting attenuation for each of the IF and UHF gain stages is plotted in Figure 9B. Again, it is pointed out that the sum of the IF and UHF gains is equal to the AGC VALUE entry. Figure 10A shows the generic gain control circuit 200 configured to perform an alternative type of variable gain LNA control. This configuration would be useful with an unchanged variable gain IF LNA 110 5 (shown in Figure 5). In this configuration, the LNA_GAIN and RX_AGC_ADJ routes are decoupled. Linearizers 190 of RX and Linearizer 210 of LNA are programmed to specify the distribution and relative gain between the IF amplifiers and Í0 UHF. The LNA_RANGE output is not used. The LNA_DECISION is overcontled to activate the multiplexer 340 for • select zero. The output of step gain control 300 in this way will be ignored. LNA_GAIN_MIN, (4) and LNA_GAIN_RANGE, (5) are programmed as described above and LNA__GAIN is adjusted accordingly. An example of the attenuation resulting for each of the IF and UHF gain stages is plotted in Figure 10B. Again, the sum of the IF and UHF gains is equal to AGC_VALUE input. The prior description of the preferred embodiments is provided to enable any person skilled in the art to make use of the present invention. The various modifications to these embodiments will be readily apparent to those skilled in the art, and the generic principles defined herein may be applied to other embodiments without the use of the inventive faculty. Thus, the present invention is not intended to be limited to the embodiments shown herein but is in accordance with the broadest scope and consistent with the principles and novel features described herein.

Claims (19)

1. NOVELTY OF THE INVENTION Having described the present invention, it is considered as a novelty and, therefore, the content of the following CLAIMS is claimed as property: 1.
2. An apparatus for performing automatic gain control (AGC) of a received signal. and providing a gain value, comprising: a chain of amplifiers comprising a plurality of gain stages for amplifying a received signal; means for receiving the amplified signal from the chain of amplifiers and calculating a gain value necessary to amplify the received signal at a reference power level; and a gain control means for receiving the gain value and generating the gain control signal for each of the plurality of gain stages such that the combined gain of each of the plurality of gain stages is equal to the value of profit The apparatus according to claim 1, further comprising a transmitting means for receiving the gain value and determining a transmit power level thereof.
3. The apparatus according to claim 1, wherein the chain of amplifiers comprises: a switchable individual gain stage capable of introducing a constant gain at a zero gain in the chain of amplifiers under the control of the gain control means; and a variable gain stage capable of introducing a variable gain in the chain of amplifiers under the control of the gain control means.
4. The apparatus according to claim 1, wherein the amplifier chain comprises: # '.10 a first variable gain stage capable of introducing a first variable gain in the chain of amplifiers under the control of the gain control means; and a second stage of variable gain capable 15 to introduce a second variable gain in the chain of amplifiers under the control of the gain control means.
5. The apparatus according to claim 1, wherein the chain of amplifiers comprises: a variable, switchable gain stage capable of introducing a first variable gain or a zero gain in the chain of amplifiers under the control of the gain control means; and a variable gain stage capable of 25 introduce a second variable gain in the chain of amplifiers under the control of the gain control means.
6. 6. An apparatus for gain control, comprising: • a linear gain control means for producing a first variable gain value in response to the full gain value, whereby: the first variable gain value is zero as long as the full gain is less than a first predetermined threshold; the first variable gain value is W10 increments linearly with the full gain while the full gain is greater than the first predetermined threshold; and the first variable gain value stops to increase once it has reached a level 15 predetermined gain maximum; a step gain control means for producing a constant gain control signal and a constant gain value in response to the full gain value whereby: 20 the constant gain control signal is deactivated and the constant gain value is zero while the full gain is less than a second predetermined threshold; the constant gain control signal is 25 active and the constant gain control value is a predetermined constant gain control level while the full gain is greater than a third predetermined threshold; and the constant gain control signal is subjected to hysteresis between deactivation and • activation and the constant gain value is subjected to hysteresis between zero and the predetermined constant gain level as long as the full gain is between the second predetermined threshold and the third predetermined threshold; a means added to produce a second variable gain which is the sum of: the full gain value; the negative of the predetermined constant gain level when the constant gain control signal is activated; and negative of the first control value of 15 constant gain.
7. 7. An apparatus for gain control comprising: a linear gain control means for producing a first variable gain value in Response to a full gain value whereby: the first variable gain value is zero while the full gain is less than a first predetermined threshold; The first variable gain value is linearly increased with the full gain as long as the complete gain is greater than the first predetermined threshold; the first variable gain value ceases to increase once it has reached a predetermined maximum gain level; a gain control means per step to produce a constant gain control signal and a constant gain value in response to a full gain value, whereby: the constant gain control signal is deactivated and the gain value constant is zero as long as the complete gain is less than a second predetermined threshold; the constant gain control signal is activated and the constant gain value is a predetermined constant gain level while the full gain is greater than a third predetermined threshold; and the constant gain control signal is subjected to hysteresis between deactivation and activation and the constant gain value is subjected to hysteresis between zero and the predetermined constant gain level while the complete gain is between the second predetermined threshold and the third predetermined threshold; a first adding means for producing the sum of the constant and programmable gain value to zero or the first variable gain value; and a second adding means for producing a second variable gain which is the sum of the full gain value and either the negative of the output of the first adding means when the constant gain control signal is set to zero when the control signal of Constant gain is disabled.
8. The apparatus according to claim 6, wherein the constant gain control signal is -OR can overcontrol programmable to be activated or deactivated.
9. 9. The apparatus according to claim 7, wherein the constant gain control signal can be over-controlled in a programmable manner to be 15 disabled or activated.
10. 10. An apparatus for gain control, comprising: step control means for producing a stage bypass control signal 20 gain in response to a full gain value; a linear gain control means for producing a first variable gain value in response to the full gain value; 25 an adding means for producing a second variable gain control value as the difference between the full gain value and any gain introduced under the control of the step control means and the linear gain control means.
11. 11. The apparatus according to claim 6, further comprising: a filter for filtering the full gain control value; a first multiplexer for selecting between the full gain control value and the filter output to be input to the control means of Wr gain by steps; a second multiplexer for selecting between the full gain value and the filter output to be input to the linear gain control means.
12. 12. The apparatus according to claim 7, further comprising: a filter for filtering the full gain control value; a first multiplexer to select between 20 the full gain control value and the filter output for introduction to the gain control means per step; a second multiplexer to select between the full gain control value and the 25 filter output to enter the linear gain control means.
13. The apparatus according to claim 8, further comprising: a filter for filtering the full gain control value; a first multiplexer for selecting between the full gain value and the filter output to enter the gain control means per step; a second multiplexer for selecting between the full gain control value and the filter output to introduce the linear gain control means ffti.
14. The apparatus according to claim 9, further comprising: a filter for filtering the full gain control value; a first multiplexer for selecting between the full gain value and the filter output to enter the gain control means per step; a second multiplexer to select 20 between the full gain control value and the filter output to be input to the linear gain control means.
15. The apparatus according to claim 10, further comprising: a filter for filtering the full gain control value; a first multiplexer for selecting between the full gain value and the filter output to enter the gain control means per step; • a second multiplexer to select between the full gain control value and the filter output to be input to the linear gain control means.
16. 16. An apparatus for gain control comprising: a plurality of gain control means for producing a plurality of gain values in response to a full gain value; an adding means to produce an additional gain value that is the value difference 15 full of profit and the sum of the plurality of profit values.
17. 17. A method for gain control comprising: producing a plurality of values of 20 gain for the plurality of gain control means in response to a full gain value; produce an additional gain value by subtracting the sum of the plurality of values from 25 gain of the full value of profit.
18. 18. A method for performing automatic gain control (AGC) and a received signal and providing a gain value, comprising: amplifying a received signal with a chain of amplifiers comprising a plurality of gain stages; receiving the amplified signal from the chain of amplifiers and calculating - a gain value necessary to amplify the received signal at a reference power level; and receive the gain value and generate the gain control signals for each of the '10 a plurality of gain stages such that the combined gain of each of the plurality of gain stages is equal to the gain value
19. 19. The method according to claim 18, further comprising a step. to receive the value of 15 gain and determine a power transmission level thereof.