An adaptive amplification circuit for wireless optical communication signal processing

Abstract

The application discloses an adaptive amplification circuit for wireless optical communication signal processing, and relates to the technical field of wireless optical communication signal processing, and specifically relates to an adaptive amplification circuit for wireless optical communication signal processing, which is characterized by comprising a main amplification circuit, an inner feedback loop, an outer feedback loop and a weighting adjustment circuit.

Description

Technical Field

[0001] This invention relates to the field of optoelectronic communication technology, and more specifically to an adaptive amplifier circuit for wireless optical communication signal processing. Background Technology

[0002] In wireless optical communication systems, light-emitting diodes (LEDs) or laser diodes (LDs) are typically used as the transmitter. By modulating the driving current, the information to be transmitted is loaded onto the optical signal and radiated into space. At the receiver, photodiodes or other photosensitive devices are generally used to detect the incident light signal and convert it into a corresponding electrical signal. However, due to issues such as light intensity attenuation and environmental noise interference in the wireless optical channel, the amplitude of the electrical signal obtained at the receiver is usually small, making it difficult to directly demodulate and process it. Therefore, an amplifier circuit is needed to effectively amplify the weak electrical signal to improve the system's signal-to-noise ratio and communication reliability.

[0003] However, the amplitude of the electrical signal output by the optoelectronic devices in visible light communication receivers is typically small, and in practical applications, it is easily affected by factors such as ambient light noise, background light variations, and channel fading. The amplitude and signal-to-noise ratio of the received signal fluctuate significantly with environmental conditions, thus placing more stringent requirements on the receiver amplifier circuit in terms of gain accuracy, dynamic response capability, and system stability. On the one hand, the amplifier circuit needs to provide sufficient and stable gain to ensure reliable detection of weak optoelectronic signals; on the other hand, it also requires good transient response characteristics and stability to adapt to application scenarios in wireless optical communication where modulation frequencies are high and signal changes are rapid. In existing wireless optical communication receiver amplifier circuits, some schemes adopt a fixed-gain amplification structure. This type of structure is simple to implement, but its gain cannot be adjusted according to changes in received light intensity. Under weak light conditions, it is prone to insufficient amplification, while under strong light or close-range reception, it is prone to saturation, meaning the system's dynamic range is limited. To address the issue of insufficient environmental adaptability in fixed-gain structures, related technologies have further employed single-loop negative feedback structures to control the amplifier gain. While this approach improves gain stability to some extent, under high-gain and wide-bandwidth operating conditions, a single feedback loop is easily constrained by factors such as the operational amplifier gain-bandwidth product and phase delay, leading to insufficient system phase margin and consequently causing oscillations, response hysteresis, or signal distortion. Furthermore, it remains difficult to simultaneously maintain steady-state amplification accuracy and dynamic response capability when there are significant changes in illumination intensity or receiving distance. In addition, some studies have attempted to indirectly control gain by detecting other characteristics of the signal itself. This approach is essentially an open-loop, indirect control strategy, and its effectiveness strongly depends on the specific modulation format DCO-OFDM, making it unsuitable for widely used modulation methods such as OOK and PPM. Moreover, in dynamic channels, the AC and DC components of the signal may experience uncorrelated fading, leading to inaccurate gain control. Therefore, this approach has inherent limitations in terms of versatility and control accuracy. These existing solutions can optimize communication quality to some extent, but they cannot achieve a good balance between steady-state amplification accuracy and dynamic response capability under different channel conditions, which affects the overall performance of optical detection and communication. Summary of the Invention

[0004] Purpose of the Invention: The purpose of this invention is to provide an adaptive amplifier circuit for wireless optical communication signal processing. By introducing a weighting mechanism into the dual-loop feedback structure, the intensity of the inner and outer feedback loops can be flexibly adjusted, thereby improving the overall performance of the amplifier circuit in steady-state amplification and dynamic response under changing channel conditions and communication requirements, and solving the problems existing in the background technology.

[0005] Technical Solution: The present invention discloses an adaptive amplifier circuit for wireless optical communication signal processing, comprising: a main amplifier circuit, an inner feedback loop, an outer feedback loop, and a weighted adjustment circuit; wherein, the main amplifier circuit is used to perform variable gain amplification of the input electrical signal; it includes a signal input terminal, a signal output terminal, and a gain control terminal; the input terminal of the inner feedback loop is connected to the signal output terminal of the main amplifier circuit, and is used to generate a first feedback control signal based on the instantaneous peak value of the output signal; the input terminal of the outer feedback loop is connected to the signal output terminal of the main amplifier circuit, and is used to generate a second feedback control signal based on the effective value or average value of the output signal; the weighted adjustment circuit is connected to the inner feedback loop, the outer feedback loop, and the gain control terminal of the main amplifier circuit respectively; it is used to acquire the first feedback control signal and the second feedback control signal, and perform analog weighted summation of the two according to a preset weighting coefficient to generate a gain control voltage to adjust the gain of the main amplifier circuit.

[0006] Furthermore, the weighted adjustment circuit includes: an operational amplifier, a first weighted branch, a second weighted branch, and a feedback network; wherein the output terminal of the operational amplifier is connected to the gain control terminal of the main amplifier circuit; the first weighted branch is connected to the output terminal of the inner feedback loop and the inverting input terminal of the operational amplifier respectively; the second weighted branch is connected to the output terminal of the outer feedback loop and the inverting input terminal of the operational amplifier respectively; the feedback network is connected to the output terminal and the inverting input terminal of the operational amplifier respectively; wherein the first weighted branch includes a first input resistor; the second weighted branch includes a second input resistor; the weighting coefficients of the first weighted branch and the second weighted branch are determined by the ratio of the first input resistor, the second input resistor, and the equivalent impedance of the feedback network.

[0007] Furthermore, the second input resistor is a variable resistor used to adjust the weighting coefficient of the external feedback loop; the feedback network is a variable feedback network, and its resistance value is adjusted synchronously with the adjustment of the second input resistor to maintain the working stability of the weighted adjustment circuit.

[0008] Furthermore, the equivalent gain of the main amplifier circuit satisfies the following relationship:

[0009]

[0010] in, The total gain at the current time. The base gain of the main amplifier circuit. For the gain of the inner loop feedback unit, For the gain of the outer loop feedback unit, For weighting coefficients, 0 ≤ ≤1;

[0011] Weighting coefficient The first weighted branch resistor Second weighted branch resistance and feedback resistor / / Decide

[0012]

[0013] in It is a variable resistor, and the resistance value can be adjusted to adjust the magnitude of the weighting coefficient;

[0014]

[0015] in The voltage for gain control; A and B It is determined by the parameters of the variable gain amplifier circuit itself.

[0016]

[0017] In the formula, This is expressed as a proportionality coefficient. This is the set reference voltage value.

[0018] Furthermore, the internal feedback loop includes a peak detector and a first integral error amplifier; wherein, the input terminal of the peak detector is connected to the signal output terminal of the main amplifier circuit, and is used to extract the peak value of the output signal and convert it into a DC voltage; the first input terminal of the first integral error amplifier is connected to the output terminal of the peak detector, and the second input terminal is connected to the first reference voltage, and is used to perform integral calculation on the difference between the two to output a smooth first feedback control signal.

[0019] Furthermore, the external feedback loop includes a true RMS detector and a second integral error amplifier; wherein, the input terminal of the true RMS detector is connected to the signal output terminal of the main amplifier circuit, and is used to extract the RMS value of the output signal and convert it into a DC voltage; the first input terminal of the second integral error amplifier is connected to the output terminal of the true RMS detector, and the second input terminal is connected to the second reference voltage, and is used to perform integral calculation on the difference between the two to output a smooth second feedback control signal.

[0020] Furthermore, the main amplifier circuit includes a variable gain amplifier whose gain is linearly adjusted by a gain control voltage.

[0021] The wireless optical communication receiving system of the present invention is implemented according to any one of the amplification circuits described herein, comprising: a photoelectric conversion unit and an adaptive amplification circuit; wherein, the photoelectric conversion unit is used to convert the received optical signal into an electrical signal; the input terminal of the adaptive amplification circuit is connected to the output terminal of the photoelectric conversion unit, and is used to adaptively amplify the electrical signal.

[0022] Beneficial Effects: Compared with existing technologies, this invention has the following significant advantages: This invention improves the overall stability and dynamic response performance of the amplifier circuit through a dual-loop feedback structure. It employs a dual-loop amplification structure combining an internal feedback loop and an external feedback loop. The internal feedback loop is used for rapid response to high-frequency noise and transient disturbances, while the external feedback loop is used to adjust the overall gain and low-frequency stability. The two work together to ensure that the amplifier circuit maintains good overall stability and dynamic response performance within its operating range, avoiding the problem of a single feedback structure struggling to balance stability and response speed. This invention achieves flexible adjustment of the intensity of different feedback signals through a weighting mechanism. An analog weighting module is introduced into the dual feedback loop, and adjustable resistors are used to proportionally adjust different feedback signals. This allows the influence of internal and external feedback on the amplifier circuit to be configured as needed, thereby achieving adjustable amplification characteristics and improving the circuit's adaptability in different application scenarios.

[0023] The beneficial effects of this invention have been fully verified through specific embodiments. Under the same channel conditions, the receiving system using the amplifier circuit of this invention can adapt to different channel conditions and reduce the bit error rate by reasonably changing the weighting ratio of the branches. These results prove that this invention, through its unique weighted dual-loop design, not only improves the overall performance of the system's steady-state amplification and dynamic response, but also enhances the circuit's adaptability in different application scenarios. Attached Figure Description

[0024] Figure 1 This is a design drawing of the present invention;

[0025] Figure 2 This is a schematic diagram of the principle of the present invention;

[0026] Figure 3 This is a block diagram of a traditional single-loop feedback adaptive amplifier circuit.

[0027] Figure 4 This is a comparison diagram of the bit error rate of the fixed gain amplifier circuit and the dual-loop amplifier circuit of the present invention as a function of light intensity;

[0028] Figure 5 This is a block diagram of a visible light information and energy simultaneous transmission system using a weighted dual-loop adaptive amplifier circuit as the signal processing branch, according to the present invention.

[0029] Figure 6 This is a block diagram of a traditional single-loop feedforward adaptive amplifier circuit.

[0030] Figure 7 This is a comparison diagram of the bit error rate of the single-loop amplifier circuit and the dual-loop amplifier circuit of the present invention as a function of light intensity;

[0031] Figure 8This is a comparison chart of the bit error rate of the weighted dual-loop amplifier circuit and the unweighted dual-loop amplifier circuit of the present invention as a function of light intensity. Detailed Implementation

[0032] The technical solution of the present invention will be further described below with reference to the accompanying drawings.

[0033] This embodiment provides an adaptive amplifier circuit for wireless optical communication signal processing, such as... Figure 2 As shown, the system includes a main amplifier circuit, an internal feedback loop, an external feedback loop, and a weighted adjustment circuit. These functional modules are interconnected via signal and feedback paths, forming a dual-loop adaptive amplification structure with weighted adjustment capabilities. The main amplifier module amplifies the electrical signal output from the photoelectric conversion device and typically consists of at least one operational amplifier, including a variable gain amplifier. The input of the main amplifier module receives the voltage signal from the photoelectric conversion device after current-to-voltage conversion by a transimpedance amplifier. Its output serves as both the output signal of the amplification circuit and the feedback signal, connected to the internal and external feedback loops respectively. The weighted adjustment module is located between the main amplifier unit and the feedback loop, used to perform analog weighting processing on the feedback signals from different feedback paths. This module typically includes two weighting branches, each corresponding to one feedback signal, and uses adjustable resistors to proportionally adjust the feedback signals. The internal feedback loop module samples the signal from the output of the main amplifier unit and feeds it back to the intermediate node or local input of the main amplifier unit after passing through the weighted adjustment unit. The internal feedback loop is primarily used to adjust the dynamic response characteristics of the amplifier circuit and suppress high-frequency noise and transient oscillations. By changing the weighting ratio of the internal feedback signal in the weighted adjustment unit, the influence of the internal feedback loop on the system's dynamic characteristics can be adjusted. The external feedback loop module samples the signal from the output of the main amplifier unit and feeds it back to the input of the main amplifier unit after passing through the weighted adjustment module. This external feedback loop is mainly used to set the overall closed-loop gain of the amplifier circuit, improve amplification accuracy, and enhance the circuit's robustness to device parameter drift and environmental changes. By adjusting the weighting ratio of the internal and external feedback signals in the weighted adjustment unit, the influence of the internal and external feedback loops on the system gain can be changed.

[0034] Reference Figure 1The main amplifier circuit includes a variable gain amplifier, the Texas Instruments (TI) VCA810, offering a wide-range voltage-adjustable gain of up to 80dB (–40dB to +40dB), with a constant -3dB bandwidth of 35MHz across the entire gain range. The gain is precisely adjusted linearly at a rate of 40dB / V by an external control voltage (0V to –2V). The chip is configured for non-inverting amplification mode: the power supply terminals (+VS, –VS) are connected to +... The circuit is powered by a -5V power supply and equipped with two decoupling capacitors C2, C3 and C4, C5, respectively, located close to the pins. The ground terminal (GND) is directly connected to the system common ground. The input signal, after being DC-blocked by coupling capacitor C1, is connected to its non-inverting input (+In) through bias resistor R1. The inverting input is grounded through matching resistor R2. The output terminal (VOUT) is connected to R3, one end of which is connected to the negative feedback loop (NET1), and the other end is grounded and filtered through R4 and capacitor C10. The feedback control voltage signal is input from (RE), passes through variable potentiometer PR1 and resistor R10, and is connected to the gain control terminal (Gain) to control the gain. The internal feedback loop includes a closed-loop control circuit consisting of an integrated peak detector and an integral error amplifier. The peak detector uses a Linear Technology LTC5507 chip (U2). Its power supply terminal (VCC) is connected to the power supply and filtered through a decoupling network consisting of capacitors C7 and C8. The peak hold capacitor terminal (PCAP) is connected to ground via capacitor C9; the value of this capacitor determines the detector's response speed. Its shutdown control terminal (SHDN) is grounded through resistor R8, configured for always-enabled operation. Its signal input terminal (RFIN) is connected to the signal sampling point through a network consisting of resistors R6 and R7. The peak hold capacitor terminal is connected to ground to set the response characteristics. The detected voltage is finally led out from the output terminal (VOUT). The integral error amplifier uses an Analog Devices Inc. AD820 chip. Its positive power supply terminal (+VS) is connected to the corresponding power supply and decoupled locally through decoupling capacitors C17 and C18. The negative power supply terminal (–VS) is grounded. It is configured as an integrator: the output (VOUT) of the peak detector is connected to the non-inverting input (+IN) of the AD820 chip via resistor R8; the inverting input (–IN) of the AD820 chip is connected to the reference voltage node between PR3 and R10, and the reference voltage can be adjusted by adjusting PR3; an integral feedback network consisting of capacitor C12 and resistor R11 is connected in parallel between the non-inverting input and output of the AD820 chip, and its output is output to the weighted adjustment circuit (NET2) via resistor R9 to provide a final smoothed control voltage. This scheme extracts the signal envelope by integrating the peak detector, and generates a precise control voltage after comparing it with the reference voltage, thus achieving a fast response to signal peaks.

[0035] The core of the external feedback loop consists of a true RMS detector and an integrating error amplifier. The true RMS detector uses the AD8361 chip (U4) from Analog Devices Inc. Its positive power supply terminal (VPOS) is connected to the power supply VCC and filtered by decoupling capacitors C13 and C14; the common terminal (COMM) is grounded. The AC signal to be detected is input to the input terminal (RFIN) via the signal sampling nodes of resistors R12 and R13. The chip's reference current terminal (IREF), reference selection terminal (SREF), and shutdown terminal (PWDN) are connected to ground according to the device's recommended configuration to ensure the chip operates in normal detection mode. The effective value output terminal (VRMS) of the AD8361 chip outputs a DC voltage signal proportional to the true RMS value of the input signal. This output terminal is connected to resistor R14, and capacitors C15 and C16 are connected to ground at the filter terminal (FLTR) to set the response bandwidth of the detector output and suppress high-frequency ripple. The integral error amplifier uses the AD820 chip (U5) from Analog Devices Inc. Its positive power supply terminal (+VS) is connected to the corresponding power supply and is locally decoupled through decoupling capacitors C17 and C18, while the negative power supply terminal (–VS) is grounded. The inverting input terminal (–IN) of the AD820 chip is connected to the reference voltage node between PR4 and R15, and the reference voltage can be adjusted by adjusting PR3; the non-inverting input terminal (+IN) of the AD820 is connected to the output terminal of the true RMS detector. An integral feedback network consisting of resistor R17 and capacitor C19 is connected in parallel between the output terminal (VOUT) and the non-inverting input terminal (+IN) of the AD820, enabling the AD820 to operate in integral amplifier mode. Through this integral feedback structure, the output voltage integrates with the input error over time, thereby obtaining a smooth and stable control voltage. This control voltage is led out from the output terminal and output to the control node (NET2) through resistor R16 for gain or drive adjustment of subsequent circuits. With the above structure, the inner loop uses a true RMS detector to accurately detect the average power of the input signal, compares the detection result with the adjustable reference voltage, and generates a stable control voltage after integration, thereby realizing closed-loop regulation of the signal amplitude based on the average energy, which constitutes the mean feedback path of the inner loop control system of this invention.

[0036] The weighted adjustment circuit includes a first weighted branch and a second weighted branch. The first weighted branch is used to weight the feedback signal of the inner feedback loop, and the second weighted branch is used to weight the feedback signal of the outer feedback loop. Each weighted branch adjusts the feedback signal proportionally through a resistor network. The operational amplifier U6 can be a Texas Instruments TLV07 series or similar high-precision amplifier chip. Its positive power supply terminal (+VS) and negative power supply terminal (–VS) are connected to the corresponding power supply and ground, respectively, and power supply decoupling and noise suppression are achieved through capacitors C20 and C21. The feedback signal input (NET2) of the inner feedback loop is connected to the inverting input terminal (–IN) of the operational amplifier through an input resistor such as R18, and the feedback signal (NET3) of the outer feedback loop is connected to PR5. The non-inverting input terminal (+IN) of the operational amplifier is grounded through a resistor. The feedback network consists of a fixed resistor R19 and an adjustable resistor PR6 connected in series between the operational amplifier output (VOUT) and the inverting input (–IN), forming deep negative feedback. By adjusting the resistance values ​​of PR5 and PR6, the weights of each input branch can be changed. The weighting coefficient of each input branch is determined by the ratio of the corresponding input resistor to the total feedback resistance. By independently selecting or adjusting each input resistor, the weights of each input signal can be independently allocated and precisely set. The output VOUT of the operational amplifier is connected to the subsequent control node (RE), thereby outputting the weighted summed signal to the gain control terminal of the main amplifier circuit. With the above structure, this circuit uses an inverting summing amplifier to proportionally superimpose each input signal and uses adjustable resistors to flexibly configure and calibrate the weighting coefficients, forming a highly flexible analog weighted fusion circuit.

[0037] Example 1: This example provides a visible light signal-to-energy simultaneous transmission system using a weighted dual-loop adaptive amplifier circuit as the signal processing branch, such as... Figure 5 As shown, the system includes a transmitter LED driver unit, an LED unit, a receiver photoelectric conversion unit, a decoupling unit, an energy harvesting unit, an adaptive amplification unit, and a demodulation unit. An AC signal is coupled with a DC bias, and the driver circuit drives the LED unit to emit a light signal. This signal is transmitted through a visible light channel. The photoelectric conversion unit converts the incident light signal into an electrical signal, which is then decoupled and output as an AC signal to the adaptive amplification unit. The output signal of the adaptive amplification unit is used for demodulation by the demodulation unit, and is also fed back to the inner and outer feedback loops for weighted summation to determine the gain. The inner feedback unit is used for peak detection to detect rapid fluctuations in the output signal, and its feedback signal is weighted by a first weighting coefficient. a The weighted signal is used to quickly adjust the gain of the main amplifier circuit. The outer loop feedback unit is used for mean value detection to detect the average amplitude of the output signal, and its feedback signal is processed by the second weighting coefficient. The weighted average is used to compensate for slow drift, ensuring that the equivalent gain of the main amplifier circuit satisfies the following relationship:

[0038]

[0039] in, The total gain at the current time. The base gain of the main amplifier circuit. For the gain of the inner loop feedback unit, This represents the gain of the outer loop feedback unit. For weighting coefficients, 0 ≤ ≤1.

[0040] Weighting coefficient The first weighted branch resistor The second weighted branch resistor and feedback resistor / / Decide / / .

[0041]

[0042] in It is a variable resistor, and the resistance value can be adjusted to adjust the weighting coefficient.

[0043]

[0044] in The voltage for gain control; A and B It is determined by the parameters of the variable gain amplifier circuit itself.

[0045]

[0046] In the formula, This is the proportionality coefficient. For the set reference voltage value, the adaptive amplifier circuit of this invention will... CC Set in the circuit , This represents the voltage of the input gain control circuit. From the equation, we can see that... It is a fixed value set when the input voltage... When increased, the gain control voltage It will decrease. Similarly, when When decreased, the gain control voltage Increase.

[0047] By feeding back signals from the inner and outer loops, the two feedback loops work collaboratively in two different dimensions: peak and mean. The inner loop provides rapid suppression during sudden noise changes or rapid changes in light intensity, while the outer loop provides steady-state compensation during slow changes in light intensity, thus achieving a combination of steady-state amplification and dynamic response performance. Figure 8 Different weights are introduced into the two branches, and the weight size can be determined according to the actual environment, which enhances the adaptability of the adaptive circuit in different application scenarios.

[0048] Comparative Example 1: Fixed Gain Amplifier Circuit

[0049] As the first comparative example of this invention, Comparative Example 1 employs a fixed-gain amplifier circuit. Its gain is preset by a resistor network and remains constant during operation, unaffected by changes in input signal amplitude or ambient light intensity. This circuit has a simple structure, containing only a single-stage operational amplifier and a fixed feedback resistor, without introducing feedback adjustment or adaptive control loops. In this amplifier circuit, the inverting input and output of the operational amplifier are connected via a feedback resistor. Connected, the input terminal is connected through an input resistor. The output signal from the photodetector is used to form a standard inverting amplifier structure, and its voltage gain is expressed by the formula:

[0050]

[0051] Once the parameters of each component in the circuit are determined during the design phase, they remain unchanged during system operation.

[0052] A fixed-gain amplifier circuit linearly amplifies the input signal using a fixed ratio. When the output signal from the photoelectric converter is input to the amplifier circuit, the operational amplifier operates in the linear region under negative feedback, and the output signal... V out With input signal V in Proportional relationship, that is

[0053] V out = G × V in

[0054] Wherein gain G A pre-defined constant.

[0055] In wireless optical communication receiving scenarios, when the ambient light intensity is within a certain range, a fixed-gain amplifier circuit can amplify weak photoelectric signals, and the system bit error rate remains within an acceptable range. However, as the incident light intensity gradually increases, the amplitude of the output signal of the photoelectric converter increases significantly, and the fixed-gain amplifier circuit is prone to entering the nonlinear operating region, leading to signal clipping, increased distortion, and a rapid increase in the system bit error rate. Conversely, when the light intensity is too low, the fixed gain cannot simultaneously meet noise suppression and sensitivity requirements, resulting in a reduced signal-to-noise ratio and also causing a deterioration in the bit error rate.

[0056] like Figure 4 When the light intensity is low, the signal-to-noise ratio is low and the bit error rate is high. As the light intensity increases to a certain extent, the fixed-gain amplifier circuit saturates and distorts, further increasing the bit error rate. Under the same conditions, the dual-loop amplifier circuit has a significantly lower bit error rate than the fixed-gain amplifier circuit. The fixed-gain amplifier circuit has poor adaptability in application scenarios with large variations in lighting conditions and cannot maintain stable bit error performance over a wide dynamic range. This comparison fully demonstrates the technical advantages of introducing a single-loop or dual-loop adaptive amplification structure in reducing the bit error rate and improving system robustness.

[0057] Comparative Example 2: Single-Loop Feedback Adaptive Amplifier Circuit

[0058] As a second comparative example of the present invention, Comparative Example 2 considers a single-loop adaptive amplifier circuit structure, which is widely used in optical communication receiving front-ends and photoelectric detection systems to compensate for the influence of light intensity variations on the received signal amplitude within a certain range. The structure of Comparative Example 2 is as follows: Figure 3 As shown, it mainly includes photoelectric conversion, current-voltage conversion, main amplification circuit, and single feedback regulation loop.

[0059] The photoelectric conversion unit converts the received optical signal into a current signal, with its output current proportional to the incident light power. After converting the current signal into a voltage signal, it is sent to the main amplifier circuit for further amplification. The output of the main amplifier circuit serves as both the system output and, via a single-loop feedback channel, returns to the amplifier control terminal to adjust the equivalent gain of the amplifier circuit. The gain factor is determined as follows: the main amplifier operates in gain mode, and the gain control voltage... Increasing the value will increase the gain. The formula for gain control is expressed as: .in, The base gain of the main amplifier circuit. The gain of the main amplifier circuit is adjusted for the feedback channel.

[0060] The gain decreases as the control voltage increases. The gain control formula at this point is:

[0061]

[0062] in The voltage for gain control; A and B It is determined by the parameters of the variable gain amplifier circuit itself.

[0063]

[0064] In the formula, This is the proportionality coefficient. For the set reference voltage value, the adaptive amplifier circuit of this invention will... CC Set in the circuit , This represents the voltage of the input gain control circuit. From the equation, we can see that... It is a fixed value set when the input voltage... When increased, the gain control voltage It will decrease. Similarly, when When decreased, the gain control voltage Increase.

[0065] Single-loop adaptive amplifier circuits are simple in structure and can adjust the gain of input signal amplitude changes within a certain range. However, this single-loop structure concentrates noise suppression and illumination change compensation in the same feedback loop, making it difficult to simultaneously achieve fast response and steady-state stability. When the illumination intensity changes significantly or the noise level is high, the single feedback loop is prone to adjustment lag or over-adjustment, leading to increased fluctuations in the amplifier's output amplitude. Under weak light or rapidly changing illumination conditions, this structure has limited noise suppression capabilities, thus limiting communication performance. Therefore, single-loop adaptive amplifier circuits are insufficient to meet the application requirements of high-reliability optical communication systems in complex illumination and high-noise environments.

[0066] To visually compare the differences between these two types of amplifier circuits and the core advantages of this invention, we compared the bit error rates of visible light communication systems employing these two amplifier circuits (e.g., Figure 7 As shown in the figure, under the same conditions, the bit error rate of the weighted dual-loop adaptive amplifier circuit is better than that of the single-loop adaptive amplifier circuit. This strongly demonstrates that the weighted dual-loop adaptive amplifier circuit proposed in this invention improves the overall performance of the system in terms of steady-state amplification accuracy and dynamic response capability, which is beneficial to the improvement of the communication quality of the entire system.

[0067] Comparative Example 3: Single-Loop Feedforward Adaptive Amplifier Circuit

[0068] As the third comparative example of the present invention, Comparative Example 3 employs a single-loop adaptive amplifier circuit structure based on DC bias. This circuit uses a feedforward structure, such as... Figure 6The circuit includes photoelectric conversion, current-to-voltage conversion, DC bias feedback control, variable gain amplification, and fixed gain amplification. The photoelectric conversion device converts the received optical signal into a photocurrent signal, which is then converted into a voltage signal by a transimpedance amplification unit and input to the variable gain amplification unit for amplification. The output signal of the variable gain amplification unit is low-pass filtered to extract its DC bias component. The extracted DC bias component is used as a feedforward signal and compared with a preset reference level. Based on the comparison result, the gain of the variable gain amplification unit is adjusted so that the average level of the output signal is maintained within a predetermined range, thereby achieving adaptive compensation for changes in light intensity.

[0069] This comparative amplifier scheme adjusts the gain of the amplifier circuit through a single feedback loop. When the channel conditions are simple, it can avoid the problems of amplifier saturation or insufficient signal amplitude to a certain extent. However, since its effectiveness strongly depends on the specific modulation format DCO-OFDM, the adaptive adjustment is based only on the DC bias component, the feedback dimension is single, and it relies on low-pass filtering to extract DC information. Under conditions of rapid changes in illumination or complex channel conditions, the DC bias component and AC component may experience uncorrelated fading. This comparative amplifier circuit has certain limitations in terms of gain adjustment stability.

Claims

1. An adaptive amplifier circuit for wireless optical communication signal processing, characterized in that, include: The system comprises a main amplifier circuit, an internal feedback loop, an external feedback loop, and a weighted adjustment circuit. The main amplifier circuit amplifies the input electrical signal with variable gain. It includes a signal input terminal, a signal output terminal, and a gain control terminal. The input terminal of the internal feedback loop is connected to the signal output terminal of the main amplifier circuit and generates a first feedback control signal based on the instantaneous peak value of the output signal. The input terminal of the external feedback loop is connected to the signal output terminal of the main amplifier circuit and generates a second feedback control signal based on the effective value or average value of the output signal. The weighted adjustment circuit is connected to the gain control terminals of the internal feedback loop, the external feedback loop, and the main amplifier circuit. It acquires the first and second feedback control signals and performs a simulated weighted summation of them according to preset weighting coefficients to generate a gain control voltage to adjust the gain of the main amplifier circuit. The internal feedback loop includes... The system comprises a peak detector and a first integrating error amplifier. The input terminal of the peak detector is connected to the signal output terminal of the main amplifier circuit to extract the peak value of the output signal and convert it into a DC voltage. The first integrating error amplifier has its first input terminal connected to the output terminal of the peak detector and its second input terminal connected to a first reference voltage. It integrates the difference between the two voltages and outputs a smooth first feedback control signal. The external feedback loop includes a true RMS detector and a second integrating error amplifier. The input terminal of the true RMS detector is connected to the signal output terminal of the main amplifier circuit to extract the effective value of the output signal and convert it into a DC voltage. The first input terminal of the second integrating error amplifier is connected to the output terminal of the true RMS detector and its second input terminal connected to a second reference voltage. It integrates the difference between the two voltages and outputs a smooth second feedback control signal.

2. The adaptive amplifier circuit for wireless optical communication signal processing according to claim 1, characterized in that, The weighted adjustment circuit includes: an operational amplifier, a first weighted branch, a second weighted branch, and a feedback network; wherein the output of the operational amplifier is connected to the gain control terminal of the main amplifier circuit; the first weighted branch is connected to the output of the inner feedback loop and the inverting input of the operational amplifier; the second weighted branch is connected to the output of the outer feedback loop and the inverting input of the operational amplifier; the feedback network is connected to the output of the operational amplifier and the inverting input; wherein the first weighted branch includes a first input resistor; the second weighted branch includes a second input resistor; the weighting coefficients of the first weighted branch and the second weighted branch are determined by the ratio of the first input resistor, the second input resistor, and the equivalent impedance of the feedback network.

3. The adaptive amplifier circuit for wireless optical communication signal processing according to claim 2, characterized in that, The second input resistor is a variable resistor used to adjust the weighting coefficient of the external feedback loop; the feedback network is a variable feedback network, and its resistance value is adjusted synchronously with the adjustment of the second input resistor to maintain the working stability of the weighted adjustment circuit.

4. The adaptive amplifier circuit for wireless optical communication signal processing according to claim 1, characterized in that, The equivalent gain of the main amplifier circuit satisfies the following relationship: ； in, The total gain at the current time. The base gain of the main amplifier circuit. For the gain of the inner loop feedback unit, The gain of the outer loop feedback unit; For weighting coefficients, 0 ≤ ≤1; Weighting coefficient The first weighted branch resistor Second weighted branch resistance and feedback resistor / / Decide: ； in The resistor is a variable resistor; adjusting its resistance value adjusts the weighting coefficient. ； in The voltage for gain control; A and B Determined by the parameters of the variable gain amplifier circuit itself; ； In the formula, This is expressed as a proportionality coefficient. This is the set reference voltage value.

5. The adaptive amplifier circuit for wireless optical communication signal processing according to claim 1, characterized in that, The main amplifier circuit includes a variable gain amplifier whose gain is linearly adjusted by a gain control voltage.

6. A wireless optical communication receiving system, characterized in that, The amplifier circuit according to any one of claims 1-5 includes: a photoelectric conversion unit and an adaptive amplifier circuit; wherein the photoelectric conversion unit is used to convert the received optical signal into an electrical signal; the input terminal of the adaptive amplifier circuit is connected to the output terminal of the photoelectric conversion unit, and is used to adaptively amplify the electrical signal.

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