Patent Description:
Because the downlink gain of a radio unit (RU) may vary with factors such as temperature and frequency, it needs to be adjusted dynamically to implement a required target gain. <FIG> shows an existing solution for downlink gain compensation. As shown, an output radio frequency (RF) signal (denoted as Pout) from a power amplifier (PA) <NUM> is the outcome obtained by applying a series of processing to an input baseband signal (denoted as Pin). Note that some of the processings are omitted in <FIG> for brevity. In order to determine the current gain between the output and input signals, a receiver <NUM> (which may be called a transmission observation receiver (TOR) in this document for an illustration purpose), down coverts the output RF signal to a baseband or intermediate frequency (IF) signal (which may be called an observation signal for an illustration purpose) by, for example, a gain adjuster <NUM> (which may be called TOR gain adjuster (TGA) for an illustration purpose), a RF downconverting mixer <NUM>, a bandpass filter <NUM> and an analog to digital converter (ADC) <NUM>. Note that when taking the form of an IF signal, the observation signal is further converted to baseband by the digital section of the RU.

Then, a temperature/frequency compensation block <NUM> generates a correction signal according to the current temperature and frequency information provided from the TOR <NUM>. The correction signal is added to the observation signal by a digital adder <NUM> to compensate gain and phase variations due to the current temperature and frequency. Then, a software (SW) <NUM>, which is executed on the RU processor, obtains power values of the input signal and the corrected observation signal via power meters <NUM>-<NUM> and <NUM>-<NUM>, respectively, so as to determine the current gain from the power values. Then, the SW <NUM> controls a voltage variable amplifier (VVA) <NUM> to compensate a gain difference between a target gain and the current gain.

For the above existing solution, there is still some room for improvement.

<CIT> describes a wireless communication unit comprising a transmitter having a forward path comprising a power amplifier (PA) and a feedback path arranged to feed back a portion of a signal output from the PA to a point in the forward path prior to the PA. The forward path and feedback path form a constant gain tracking (CGT) loop. The feedback path comprises an adaptive predistortion logic module located outside of the CGT loop and arranged to form an APD loop with the forward path and feedback path. The CGT loop comprises a controller logic module arranged to determine a gain offset of a signal routed through the forward path and feedback path and in response thereto set a drive level of the PA.

<CIT> describes a system and method for controlling the gain in the forward signal path of a digital predistortion linearizer. The loop gain of the predistortion system is driven to unity, where a separately controlled constant-gain observation path allows accurate gain control of the forward path. This is divided into digital gain from the predistortion function and analog gain from a Voltage Variable Attenuator (WA) in the transmitter.

This summary is provided to introduce a selection of concepts in a simplified form that are further described below in detailed description.

The invention is defined by the appended independent claims and the preferred embodiments are defined by the dependent claims.

One of the objects of the disclosure is to provide an improved solution for downlink gain compensation.

According to one aspect of the disclosure, there is provided a device for use in a radio unit (RU). The device comprises a pre-distortion circuit, a digital gain adjuster (GA), a gain determiner and a first gain controller. The pre-distortion circuit is configured to generate and apply a pre-distortion to an input signal. The digital GA is configured to apply an adjustable gain to an output signal from the pre-distortion circuit. The gain determiner is configured to determine a gain difference between a target downlink gain and current downlink gain. The first gain controller is configured to control the digital GA based on the gain difference.

The RU comprises an analog GA and a second gain controller. The analog GA is configured to apply an adjustable gain to an output from the digital GA. The second gain controller is configured to perform a preliminary gain adjustment via the analog GA and then trigger the gain determiner to determine the gain difference.

The first gain controller is further configured to control the analog GA via the second gain controller based on the gain difference.

In an embodiment of the disclosure, the RU comprises a power amplifier (PA) and an observation receiver. The PA is configured to amplify an output from the analog GA. The observation receiver is configured to process an output from the PA to feed back an observation signal to the pre-distortion circuit. The gain difference is determined from: a compensation gain corresponding to current working frequency and temperature; a power difference between the observation signal and the input signal received by the pre-distortion circuit; and residual gain and phase errors obtained from the pre-distortion circuit.

The first gain controller is configured to control the digital GA by determining a first adjustment amount of the digital GA based on the gain difference. The first gain controller is configured to control the digital GA by determining a next gain of the digital GA based on the first adjustment amount and current applied gain of the digital GA. The first gain controller is configured to control the digital GA by configuring the next gain to the digital GA.

The first gain controller is configured to determine the first adjustment amount by comparing the gain difference with a preset first adjustment step of the digital GA. The first gain controller is configured to determine the first adjustment amount by, when the gain difference is smaller than the first adjustment step, setting the first adjustment amount as the gain difference. The first gain controller is configured to determine the first adjustment amount by, when the gain difference is greater than or equals to the first adjustment step, setting the first adjustment amount as the first adjustment step.

In an embodiment of the disclosure, the first gain controller is configured to determine the next gain by comparing a first sum of the first adjustment amount and the current applied gain with an adjustment range of the digital GA. The first gain controller is configured to determine the next gain by, when the first sum is greater than an upper limit of the adjustment range, setting the next gain as a difference between the first adjustment amount and a second adjustment step of the analog GA. The first gain controller is configured to determine the next gain by, when the first sum is within the adjustment range, setting the next gain as the first sum. The first gain controller is configured to determine the next gain by, when the first sum is smaller than a lower limit of the adjustment range, setting the next gain as a second sum of the first adjustment amount and the second adjustment step.

In an embodiment of the disclosure, the first gain controller is configured to control the analog GA via the second gain controller by, when the first sum is greater than the upper limit of the adjustment range, setting a second adjustment amount of the analog GA as the second adjustment step. The first gain controller is configured to control the analog GA via the second gain controller by, when the first sum is smaller than the lower limit of the adjustment range, setting the second adjustment amount as an opposite value of the second adjustment step. The first gain controller is configured to control the analog GA via the second gain controller by configuring the second adjustment amount to the analog GA via the second gain controller.

According to another aspect of the disclosure, there is provided a method implemented at a device for use in a RU. The device comprises a pre-distortion circuit and a digital GA. The pre-distortion circuit is configured to generate and apply a predistortion to an input signal. The digital GA is configured to apply an adjustable gain to an output signal from the pre-distortion circuit. The method comprises determining a gain difference between a target downlink gain and current downlink gain. The method further comprises controlling the digital GA based on the gain difference.

The RU comprises an analog GA and a second gain controller. The analog GA is configured to apply an adjustable gain to an output from the digital GA. The second gain controller is configured to perform a preliminary gain adjustment via the analog GA. The gain difference is determined in response to a trigger signal from the second gain controller.

The method further comprises controlling the analog GA via the second gain controller based on the gain difference.

Controlling the digital GA comprises determining a first adjustment amount of the digital GA based on the gain difference. Controlling the digital GA further comprises determining a next gain of the digital GA based on the first adjustment amount and current applied gain of the digital GA. Controlling the digital GA further comprises configuring the next gain to the digital GA.

Determining the first adjustment amount comprises comparing the gain difference with a preset first adjustment step of the digital GA. Determining the first adjustment amount further comprises, when the gain difference is smaller than the first adjustment step, setting the first adjustment amount as the gain difference. Determining the first adjustment amount further comprises, when the gain difference is greater than or equals to the first adjustment step, setting the first adjustment amount as the first adjustment step.

In an embodiment of the disclosure, determining the next gain comprises comparing a first sum of the first adjustment amount and the current applied gain with an adjustment range of the digital GA. Determining the next gain further comprises, when the first sum is greater than an upper limit of the adjustment range, setting the next gain as a difference between the first adjustment amount and a second adjustment step of the analog GA. Determining the next gain further comprises, when the first sum is within the adjustment range, setting the next gain as the first sum. Determining the next gain further comprises, when the first sum is smaller than a lower limit of the adjustment range, setting the next gain as a second sum of the first adjustment amount and the second adjustment step.

In an embodiment of the disclosure, controlling the analog GA via the second gain controller comprises, when the first sum is greater than the upper limit of the adjustment range, setting a second adjustment amount of the analog GA as the second adjustment step. Controlling the analog GA via the second gain controller further comprises, when the first sum is smaller than the lower limit of the adjustment range, setting the second adjustment amount as an opposite value of the second adjustment step. Controlling the analog GA via the second gain controller further comprises configuring the second adjustment amount to the analog GA via the second gain controller.

There is provided a device for use in a RU. The device comprises a predistortion circuit, a digital GA and a device controller. The pre-distortion circuit is configured to generate and apply a pre-distortion to an input signal. The digital GA is configured to apply an adjustable gain to an output signal from the pre-distortion circuit. The device controller comprises a processor and a memory. The memory contains instructions executable by the processor, whereby the device controller is operative to determine a gain difference between a target downlink gain and current downlink gain. The device controller is further operative to control the digital GA based on the gain difference.

The device controller is operative to perform the method according to the above aspect.

According to another aspect of the disclosure, there is provided a RU comprising the device according to the above aspect.

According to another aspect of the disclosure, there is provided a computer program product. The computer program product comprises instructions which when executed by at least one processor, cause the at least one processor to perform the method according to the above aspect.

According to another aspect of the disclosure, there is provided a computer readable storage medium. The computer readable storage medium comprises instructions which when executed by at least one processor, cause the at least one processor to perform the method according to the above aspect.

The inventors of the disclosure found that the existing solution shown in <FIG> has some problems. Firstly, because the downlink gain compensation is performed by a software, the gain estimation and compensation period is relatively long (e.g., about <NUM>), such that the gain compensation step is relatively big (e.g., <NUM>.

Secondly, in a case where a digital pre-distortion (DPD) block is used for applying a pre-distortion to the input baseband signal to compensate the nonlinearity of the PA <NUM>, because the SW <NUM> is independent from the DPD block, an error transition may occur in phase compensation/gain regulation (PC/GR) calculation performed by the DPD block. Specifically, the PC/GR calculation may have already converged under current loop gain/phase. Then, a new VVA adjustment may be performed to change the loop gain/phase. This will cause the PC/GR calculation to diverge.

Thirdly, the re-convergence of the PC/GR calculation will cause instability to the DPD block. Thereby, the instantaneous performance of the DPD block will be degraded.

The present disclosure proposes a solution for downlink gain compensation at a radio unit. Hereinafter, the solution will be described in detail with reference to <FIG>.

<FIG> is a block diagram showing a device and a radio unit according to an embodiment of the disclosure. As shown, the device <NUM> comprises a pre-distortion circuit <NUM>, a digital gain adjuster (GA) <NUM>, a gain determiner <NUM> and a first gain controller <NUM>. The pre-distortion circuit <NUM> is configured to generate and apply a pre-distortion to an input signal. The digital GA <NUM> is configured to apply an adjustable gain to an output signal from the pre-distortion circuit <NUM>. The gain determiner <NUM> is configured to determine a gain difference between a target downlink gain and current downlink gain. The first gain controller <NUM> is configured to control the digital GA <NUM> based on the gain difference.

The radio unit (RU) <NUM> comprises the device <NUM>, an analog GA <NUM>, a second gain controller <NUM>, a power amplifier (PA) <NUM> and an observation receiver <NUM>. The analog GA <NUM> is configured to apply an adjustable gain to an output from the digital GA <NUM>. The second gain controller <NUM> is configured to perform a preliminary gain adjustment via the analog GA <NUM> and then trigger the gain determiner <NUM> to determine the gain difference. The second gain controller <NUM> may be further configured to control the analog GA <NUM> according to the instruction from the first gain controller <NUM>. In other words, the first gain controller <NUM> may be further configured to control the analog GA <NUM> via the second gain controller <NUM> based on the gain difference. The PA <NUM> is configured to amplify an output from the analog GA <NUM>. The observation receiver <NUM> is configured to process an output from the PA <NUM> to feed back an observation signal to the pre-distortion circuit <NUM>. The implementing details of the above components <NUM>-<NUM> in the RU <NUM> will be described below.

In order to compensate the nonlinearity of the PA <NUM>, the pre-distortion circuit <NUM> may be implemented, for example, based on various DPD technologies. In some embodiments of the present disclosure, residual gain and phase errors can be obtained from the pre-distortion circuit <NUM>.

The digital GA <NUM> may be implemented as, for example, a digital multiplier. It may have a preset first adjustment step. The gain determiner <NUM> may be implemented by using, for example, digital signal processor (DSP) and/or (FPGA). It may determine the gain difference according to the following information:.

The current working frequency and temperature values may be provided from the observation receiver <NUM>. The gain determiner <NUM> may determine the compensation gain based on the information from a database which may be passed to the gain determiner <NUM> through a shared memory by the second gain controller <NUM>. The database may store the compensation gain in association with temperature and frequency values.

The power difference between the observation signal and the input signal may be taken as a coarse gain estimate. Then, a coarse gain difference estimate may be calculated as the difference between a target downlink gain and the coarse gain estimate. In addition, each of the residual gain and phase errors may be taken as a fine gain difference estimate. Thus, the total gain difference may be constituted by the compensation gain, the coarse gain difference estimate and the fine gain difference estimates.

The analog GA <NUM> may be implemented as, for example, a VVA that is included in an in-phase and quadrature (IQ) modulator. It may have a second adjustment step. The second adjustment step may be greater than the first adjustment step of the digital GA <NUM>. In this way, a coarse gain compensation may be performed via the analog GA <NUM>, while a fine gain compensation may be performed via the digital GA <NUM>. Thus, the gain adjustment can be more accurate than the existing solution.

The PA <NUM> may be implemented as any suitable amplifier for amplifying RF signals. The observation receiver <NUM> may include, for example, a VVA, a RF downconverting mixer, a bandpass filter and an ADC.

The first gain controller <NUM> may be implemented by using, for example, digital signal processor (DSP) and/or (FPGA). The second gain controller <NUM> may be implemented by executing an application software on a processor of the RU <NUM>. Hereinafter, the operations performed by the first gain controller <NUM> and the second gain controller <NUM> will be described in detail.

Firstly, the second gain controller <NUM> performs a preliminary gain adjustment via the analog GA <NUM>. For example, after carrier setup, the second gain controller <NUM> may control the analog GA <NUM> to apply at least a predetermined gain. Suppose Gtarget denotes the target downlink gain and GPA denotes the gain applied by the PA <NUM>, such as <NUM>. Then, the predetermined gain may equal to (Gtarget - GPA).

For example, the second gain controller <NUM> may monitor the output and input of the analog GA <NUM> when controlling the analog GA <NUM> to adjust its applied gain. Once the applied gain of the analog GA <NUM> is greater than or equals to the predetermined gain, the second gain controller <NUM> may stop the preliminary gain adjustment (that is, the applied gain of the analog GA <NUM> is maintained) and trigger the gain determiner <NUM> to determine the gain difference. In this way, a subsequent gain adjustment can be triggered.

In the subsequent gain adjustment, the gain determiner <NUM> determines the gain difference between the target downlink gain and current downlink gain. The first gain controller <NUM> controls the digital GA <NUM> based on the gain difference. The first gain controller <NUM> may further control the analog GA <NUM> via the second gain controller <NUM> based on the gain difference. Since the fine gain adjustment is implemented by the hardware <NUM> and <NUM>, the gain adjustment can be faster than the existing solution.

<FIG> shows an example about how the first gain controller <NUM> controls the digital GA <NUM>. As shown, at step <NUM>, a first adjustment amount of the digital GA <NUM> is determined based on the gain difference. This step may be implemented as steps <NUM>-<NUM> of <FIG>, which will be described later.

At step <NUM>, a next gain of the digital GA <NUM> is determined based on the first adjustment amount and current applied gain of the digital GA. This step may be implemented as steps <NUM>-<NUM> of <FIG>, which will be described later.

At step <NUM>, the next gain is configured to the digital GA <NUM>. The predistortion circuit <NUM> may be controlled to stop working when the next gain is configured to the digital GA <NUM> and the current pre-distortion processing is finished. In this way, the instability of the pre-distortion circuit <NUM> may be avoided as possible.

Optionally, before the determination of step <NUM>, the first gain controller may compare the gain difference with a first predetermined threshold and a second predetermined threshold, respectively. The second threshold may be greater than the first threshold.

Then, if the gain difference is below the first threshold (e.g., <NUM>. 7dB), step <NUM> may be performed. If the gain difference is above the first threshold and below the second threshold (e.g., 3dB), the pre-distortion circuit may be reset and then the preliminary gain adjustment may be performed again. If the gain difference is above the second threshold, the preliminary gain adjustment may be performed again.

<FIG> shows an example about how the first adjustment amount of the digital GA <NUM> may be determined. As shown, at step <NUM>, the gain difference is compared with the preset first adjustment step of the digital GA <NUM>. Then, if the gain difference is smaller than the first adjustment step, the first adjustment amount is set as the gain difference at step <NUM>. On the other hand, if the gain difference is greater than or equals to the first adjustment step, the first adjustment amount is set as the first adjustment step at step <NUM>.

In this way, the first adjustment amount to be applied by the digital GA <NUM> is below the preset first adjustment step. Since the first adjustment step may be smaller than the second adjustment step of the analog GA <NUM>, a fine gain adjustment can be performed via the digital GA <NUM>.

<FIG> shows an example about how the first gain controller <NUM> controls the digital GA <NUM> and the analog GA <NUM>. As shown, after the determination of step <NUM>, a first sum of the first adjustment amount and the current applied gain of the digital GA <NUM> is compared with an adjustment range of the digital GA <NUM> at step <NUM>.

If the first sum is greater than an upper limit of the adjustment range, the next gain is set at step <NUM> as a difference between the first adjustment amount and the second adjustment step of the analog GA <NUM>. Correspondingly, a second adjustment amount of the analog GA <NUM> is set at step <NUM> as the second adjustment step. In this way, the first adjustment amount can be achieved via both the digital GA <NUM> and the analog GA <NUM>.

If the first sum is within the adjustment range, the next gain is set as the first sum at step <NUM>. In this case, the first adjustment amount can be achieved via only the digital GA <NUM>, without requiring the analog GA <NUM> to adjust its applied gain.

If the first sum is smaller than a lower limit of the adjustment range, the next gain is set at step <NUM> as a second sum of the first adjustment amount and the second adjustment step. Correspondingly, the second adjustment amount is set at step <NUM> as an opposite value of the second adjustment step. In this way, the first adjustment amount can be achieved via both the digital GA <NUM> and the analog GA <NUM>.

Then, at step <NUM>, the second adjustment amount is configured to the analog GA <NUM> via the second gain controller <NUM>. The pre-distortion circuit <NUM> may be controlled to stop working when the second adjustment amount is configured to the analog GA <NUM> and the current pre-distortion processing is finished. Then, at step <NUM>, the next gain is configured to the digital GA <NUM>.

Although it is shown in <FIG> that step <NUM> is subsequent to step <NUM>, step <NUM> is subsequent to step <NUM> and step <NUM> is subsequent to step <NUM>, it is also possible that in each of these three step groups, one step is performed simultaneously with or prior to the other step.

For example, suppose the first adjustment step ST1 of the digital GA (denoted as GA1) is <NUM>. 2dB, the first adjustment range is [GA1min, GA1max] = [0dB, <NUM>. 5dB], and the second adjustment step ST2 of the analog GA (denoted as GA2) is <NUM>. Then, if the gain difference Gdiff is <NUM>. 8dB and current applied gain (denoted as GGA1) of the digital GA is <NUM>. 4dB, the first gain adjustment amount Δ1 may be determined as ST1 = <NUM>. 2dB since Gdiff> ST1. Further, since GGA1 + Δ1 = <NUM>. 6dB > GA1max, the next gain G'GA1 may be determined as Δ1 - ST2 = -<NUM>. The second gain adjustment Δ2 may be determined as ST2 = <NUM>. That is, GGA1 will be decreased by <NUM>. 3dB and current applied gain (denoted as GGA2) of the analog GA will be increased by <NUM>. As a result, the total gain adjustment amount is <NUM>. 5dB - <NUM>. 3dB = <NUM>.

For another example, if Gdiff is -<NUM>. 5dB and GGA1 is <NUM>. 1dB, Δ1 may be determined as -<NUM>. 2dB since |Gdiff| > ST1. Further, since GGA1 + Δ1 = -<NUM>. 1dB < GA1min, G'GA1 may be determined as Δ1 + ST2 = <NUM>. The second gain adjustment Δ2 may be determined as -ST2 = -<NUM>. That is, GGA1 will be increased by <NUM>. 3dB and GGA2 will be decreased by <NUM>. As a result, the total gain adjustment amount is <NUM>. 3dB - <NUM>. 5dB = -<NUM>.

Optionally, before the second gain controller <NUM> controls the analog GA <NUM> according to the instruction from the first gain controller <NUM>, the second gain controller <NUM> may determine whether a sum of the second adjustment amount and current applied gain of the analog GA <NUM> is too high or too low.

If the sum is too high or too low, the second gain controller <NUM> may send out an alarm. On the other hand, if the sum is neither too high nor too low, the second gain controller <NUM> may configure the second adjustment amount to the analog GA <NUM>.

<FIG> is a flowchart illustrating a method implemented at a device according to another embodiment of the disclosure. The device comprises a pre-distortion circuit configured to generate and apply a pre-distortion to an input signal, and a digital GA configured to apply an adjustable gain to an output signal from the pre-distortion circuit. The method may be performed by a processor and a memory of the device.

At step <NUM>, it is determined a gain difference between a target downlink gain and current downlink gain. This step may be implemented as described above with respect to the gain determiner <NUM>. Then, at step <NUM>, the digital GA is controlled based on the gain difference. This step may be implemented as described above with respect to the first gain controller <NUM>.

<FIG> is a block diagram showing a device according to another embodiment of the disclosure. This embodiment is similar to the embodiment of <FIG> except that the hardware (the gain determiner <NUM> and the first gain controller <NUM>) is replaced with a device controller mainly implemented by software. Specifically, the device <NUM> comprises a pre-distortion circuit <NUM> configured to generate and apply a predistortion to an input signal, a digital GA <NUM> configured to apply an adjustable gain to an output signal from the pre-distortion circuit, and a device controller <NUM>. The device controller <NUM> comprises a processor <NUM> and a memory <NUM>. The memory <NUM> contains instructions which may be executed by the processor <NUM> to cause the device controller <NUM> to perform the method steps described above with reference to <FIG>.

<FIG> shows a solution for downlink gain compensation according to an embodiment of the disclosure. This embodiment is an exemplary example of the embodiment shown in <FIG>. In this example, the device is implemented as a DPD device <NUM> and the second gain controller is implemented as a software (SW) <NUM> executed on the RU processor. The other components (the VVA <NUM>, the PA <NUM>, the TOR <NUM>) may be implemented as described above with reference to <FIG>. Alternatively, the DPD controller <NUM> may be replaced with the hardware <NUM> and <NUM> as described above.

In this way, a DPD based gain compensation solution can be provided. In this solution, the DPD device tracks the gain difference and compensates the gain difference via its own "power amplifier" - the digital GA <NUM>. In case the gain difference exceeds the capability of the digital GA <NUM> (typically with an adjustment range of <NUM>~<NUM>. 5dB), the DPD device <NUM> may inform the SW <NUM> to adjust the analog VVA <NUM>.

It should be appreciated that at least some aspects of the exemplary embodiments of the disclosure may be embodied in computer-executable instructions, such as in one or more program modules, executed by one or more computers or other devices. Generally, program modules include routines, programs, objects, components, data structures, etc. that perform particular tasks or implement particular abstract data types when executed by a processor in a computer or other device. The computer executable instructions may be stored on a computer readable medium such as a hard disk, optical disk, removable storage media, solid state memory, RAM, etc. As will be appreciated by one of skill in the art, the function of the program modules may be combined or distributed as desired in various embodiments. In addition, the function may be embodied in whole or in part in firmware or hardware equivalents such as integrated circuits, field programmable gate arrays (FPGA), and the like.

References in the present disclosure to "one embodiment", "an embodiment" and so on, indicate that the embodiment described may include a particular feature, structure, or characteristic, but it is not necessary that every embodiment includes the particular feature, structure, or characteristic.

The terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the present disclosure. It will be further understood that the terms "comprises", "comprising", "has", "having", "includes" and/or "including", when used herein, specify the presence of stated features, elements, and/or components, but do not preclude the presence or addition of one or more other features, elements, components and/ or combinations thereof.

Claim 1:
A device (<NUM>) for use in a radio unit, RU (<NUM>), the device (<NUM>) comprising:
a pre-distortion circuit (<NUM>) configured to generate and apply a pre-distortion to an input signal;
a digital gain adjuster, GA (<NUM>), configured to apply an adjustable gain to an output signal from the pre-distortion circuit (<NUM>);
a gain determiner (<NUM>) configured to determine a gain difference between a target downlink gain and current downlink gain; and
a first gain controller (<NUM>) configured to control the digital GA (<NUM>) based on the gain difference, wherein the RU (<NUM>) comprises:
an analog GA (<NUM>) configured to apply an adjustable gain to an output from the digital GA (<NUM>); and
a second gain controller (<NUM>) configured to perform a preliminary gain adjustment via the analog GA (<NUM>) and then trigger the gain determiner (<NUM>) to determine the gain difference, wherein the first gain controller (<NUM>) is further configured to control the analog GA (<NUM>) via the second gain controller (<NUM>) based on the gain difference, wherein:
the first gain controller (<NUM>) is configured to control the digital GA (<NUM>) by:
determining a first adjustment amount of the digital GA (<NUM>) based on the gain difference;
determining a next gain of the digital GA (<NUM>) based on the first adjustment amount and current applied gain of the digital GA (<NUM>); and
configuring the next gain to the digital GA (<NUM>); and
the first gain controller (<NUM>) is configured to determine the first adjustment amount by:
comparing the gain difference with a preset first adjustment step of the digital GA (<NUM>);
when the gain difference is smaller than the first adjustment step, setting the first adjustment amount as the gain difference; and
when the gain difference is greater than or equals to the first adjustment step, setting the first adjustment amount as the first adjustment step.