Transimpedance amplifier for reducing settling time of burst-mode optical receiver using external control

Abstract

The application discloses a trans-impedance amplifier for reducing the stable time of a burst mode optical receiver by using an external control method, which comprises an external control pin VC, a gain control signal generating unit, a trans-impedance amplifier and a variable gain amplifier. The burst mode trans-impedance amplifier needs to process a wide dynamic range of current, and needs to adaptively adjust its own gain according to different input currents to meet the output swing requirement. The method uses an external analog signal to control the gain of the trans-impedance amplifier, and controls the change of the external analog signal according to the input current value, and sends the analog signal into the gain control signal generating unit to generate the trans-impedance amplifier gain control signal and the variable gain amplifier gain control signal. The complexity of the circuit design is reduced by reducing the gain control loop of the trans-impedance amplifier and the variable gain amplifier, and the stable time of the gain control signal is reduced. The gain adjustment under different currents is realized by changing the size of the analog signal.

Description

Technical Field

[0001] This invention belongs to the field of analog integrated circuit design technology, and particularly relates to a transimpedance amplifier that uses external control to reduce the settling time of a burst-mode optical receiver. Background Technology

[0002] Optical receivers are a crucial component of optical communication networks. Depending on the application, optical receivers typically employ either continuous mode or burst mode. In passive optical networks (PONs), uplink transmission is a point-to-point operation, and burst-mode optical receivers process data signals transmitted from different network terminals. Because the optical power transmitted by each terminal varies, and because the optical signal experiences different losses over varying fiber optic distances, the amplitude of the signals processed by burst-mode optical receivers can differ significantly.

[0003] The input signal (burst packet) of a burst-mode optical receiver mainly consists of a preamble, data, and a guard band. The preamble ensures that the burst-mode optical receiver adjusts its gain control signal within the specified time period, preparing for subsequent data transmission. The time required for the control signal to stabilize is called the settling time. If data transmission begins before the control signal stabilizes, it may lead to data distortion and affect system performance.

[0004] Channel utilization can be expressed as:

[0005] Channel utilization = Data length / (Guard band length + Preamble length + Data length)

[0006] The shorter the stabilization time, the shorter the preamble length can be, thus improving channel utilization.

[0007] For burst-mode optical receivers, low settling time is a key performance indicator that needs to be considered in circuit design.

[0008] The transimpedance amplifier in an optical receiver can be externally controlled to reduce the settling time of burst-mode optical receivers. This approach also simplifies the circuit structure, eliminating the transimpedance amplifier gain control loop and the variable gain amplifier gain control loop found in traditional circuits, thus greatly reducing circuit complexity. Chip area and power consumption are also reduced. Summary of the Invention

[0009] The purpose of this invention is to provide a transimpedance amplifier that uses external control to reduce the settling time of burst-mode optical receivers, in order to solve the technical problem that the data optical power transmitted by different terminals is different, and the loss caused by the optical signal passing through optical fibers of different distances is different, resulting in a large difference in the signal amplitude processed by burst-mode optical receivers.

[0010] To solve the above-mentioned technical problems, the specific technical solution of the present invention is as follows:

[0011] A transimpedance amplifier that uses external control to reduce the settling time of a burst-mode optical receiver includes an external analog input port, a gain control signal generation unit, a transimpedance amplifier, and a variable gain amplifier controlled by an analog voltage.

[0012] The gain control generation unit converts the signal into a first gain control signal VC1 of the transimpedance amplifier and a second gain control signal VC2 of the variable gain amplifier to achieve gain control.

[0013] Furthermore, the gain control signal generation unit includes a comparator and a subtractor;

[0014] Furthermore, the variable gain amplifier shown is based on the Gilbert unit current rudder type.

[0015] Furthermore, the variable gain amplifier includes a first amplifying tube M1, a second amplifying tube M2, a third amplifying tube M3, a fourth amplifying tube M4, a fifth amplifying tube M5, a sixth amplifying tube M6, a first current mirror tube M7, a second current mirror tube M8, and a load resistor R. L .

[0016] Furthermore, the variable gain amplifier also includes a source degradation resistor 2R. S .

[0017] The transimpedance amplifier of the present invention, which employs external control to reduce the settling time of burst-mode optical receivers, has the following advantages:

[0018] 1. The external signal control in this invention can significantly reduce the settling time of the circuit's transimpedance gain. Unlike traditional burst-mode optical receivers, which typically require an internal automatic gain control circuit to extract feedback control signals to change the circuit gain, this invention uses an external control signal to replace the feedback scheme, thereby reducing the settling time.

[0019] 2. This invention reduces the difficulty of circuit design by eliminating the automatic gain control loop of the transimpedance amplifier and the automatic gain control loop of the variable gain amplifier.

[0020] 3. The circuit structure of this invention does not add an additional gain control module, which reduces the power consumption of the circuit, reduces the circuit area, and reduces the cost. Attached Figure Description

[0021] Figure 1 The circuit diagram of the transimpedance amplifier of the present invention, which uses external control to reduce the settling time of burst-mode optical receivers;

[0022] Figure 2 The circuit diagram shows the gain control signal generation unit in the transimpedance amplifier of the present invention, which uses external control to reduce the settling time of the burst mode optical receiver.

[0023] Figure 3 The circuit diagram shows the variable gain amplifier in the transimpedance amplifier of the present invention, which uses external control to reduce the settling time of the burst-mode optical receiver. Detailed Implementation

[0024] To better understand the purpose, structure, and function of this invention, the transimpedance amplifier of this invention, which uses external control to reduce the settling time of burst-mode optical receivers, will be described in further detail below with reference to the accompanying drawings.

[0025] like Figure 1 As shown, the present invention includes an external control pin VC, a gain control signal generation unit, a transimpedance amplifier, and a variable gain amplifier controlled by an analog voltage.

[0026] The external control pin VC is an external control signal input port. After passing through the gain control signal generation unit, it is converted into the first gain control signal VC1 of the transimpedance amplifier and the second gain control signal VC2 of the variable gain amplifier, respectively, to achieve gain control.

[0027] First, considering that the photodiode and the chip are packaged in a ROSA (Receiver Optical Sub-Assembly) package, which contains two components—a photodetector and a transimpedance amplifier (TIA)—we can understand the internal structure of the ROSA package. The photodetector and the chip are packaged together, and the chip's input and the photodetector's output are connected via bonding wires. The first voltage, VPD, provides reverse bias to the photodetector, and the second voltage, VDD, is the power supply voltage, providing the chip with a 3.3V power supply. OUTP is the chip's first differential output terminal, and OUTN is the chip's second differential output terminal. Therefore, this package can only provide a maximum of one usable external control pin, VC. This invention fully utilizes this external control pin, VC, to introduce an external control signal from outside the chip to control the transimpedance gain of the circuit. The external control signal is an analog quantity; changing the magnitude of the analog quantity can achieve multiple gain levels to adapt to a wide range of dynamic input currents. External control reduces the settling time of the optical receiver. The gain control signal generation unit converts the external control signal into the control signals required by the transimpedance amplifier and the variable gain amplifier.

[0028] Then, the analog quantity provided by the external control pin VC is often not the analog quantity required by the transimpedance amplifier and the variable gain amplifier. It needs to be respectively converted into the first gain control signal VC1 of the transimpedance amplifier and the second gain control signal VC2 of the variable gain amplifier through the gain control signal generation unit to achieve gain control. While giving the second gain control signal VC2 to the variable gain amplifier, changing the second gain control signal VC2 can achieve multiple gain levels to adapt to a wide current dynamic range.

[0029] The present invention reduces the gain control loop in the traditional burst-mode transimpedance amplifier and changes it to external control. In order to generate the gain control signal, the traditional circuit often requires units such as mean detection and automatic gain control. The present invention reduces the design of the above modules, reduces the complexity of the circuit design, and also reduces the circuit power consumption and chip area.

[0030] Figure 2 Shows the working principle of the gain control signal generation unit. The gain control signal generation unit includes a comparator and a subtractor. The output terminal of the comparator is connected to the port of the gain control signal VC1 of the transimpedance amplifier and the input terminal of the subtractor at the same time, and the output terminal of the subtractor is connected to the port of the second gain control signal VC2 of the variable gain amplifier.

[0031] The external control pin VC is input to the comparator and compared with V_REF. V_REF is a reference voltage of the comparator and is provided by the low-dropout linear regulator (LDO) inside the circuit. If VC < V_REF, the output first gain control signal VC1 is at a low level; if VC > V_REF, the output first gain control signal VC1 is at a high level. The first gain control signal VC1 is input to the control terminal of the transimpedance amplifier to adjust the system gain within a large range.

[0032] The external control pin VC and the first gain control signal VC1 are input to the subtractor together to obtain the second gain control signal VC2 = external control pin VC - first gain control signal VC1. The second gain control signal VC2 is input to the control terminal of the variable gain amplifier for more detailed gain regulation.

[0033] Figure 3 The present invention adopts a variable gain amplifier based on the Gilbert cell current steering type. The variable gain amplifier includes a first amplifying transistor M1, a second amplifying transistor M2, a third amplifying transistor M3, a fourth amplifying transistor M4, a fifth amplifying transistor M5, a sixth amplifying transistor M6, a first current mirror transistor M7, a second current mirror transistor M8 and a load resistor R LThe first amplifying transistor M1 and the second amplifying transistor M2 serve as amplifying transistors for the input signal. The source terminal of the first amplifying transistor M1 is connected to the drain terminal of the first current mirror transistor M7, the source terminal of the second amplifying transistor M2 is connected to the drain terminal of the second current mirror transistor M8, the drain terminal of the first amplifying transistor M1 is connected to the source terminals of the third amplifying transistor M3 and the fourth amplifying transistor M4, and the drain terminal of the second amplifying transistor M2 is connected to the source terminals of the fifth amplifying transistor M5 and the sixth amplifying transistor M6. The load resistor R... L Connect the drain terminals of the third amplifier transistor M3 and the sixth amplifier transistor M6, the drain terminals of the fourth amplifier transistor M4 and the fifth amplifier transistor M5, and the load resistor R. L The other end is connected to the power supply voltage VDD. The current-controlled variable gain amplifier achieves gain change by altering the output current gain through a control signal, thereby changing the circuit's equivalent transconductance. Furthermore, due to the reduced number of transistors connected to the load and the advantages of the cascode structure, it achieves high bandwidth. Although the correlation between the load current and the control voltage Vctrl leads to instability at the output DC point, and nonlinear distortion is prone to occur with output signals exhibiting large swing ranges, this design only requires a 400mV output swing, thus minimizing the impact of nonlinear distortion. Additionally, the source degradation resistor 2R... S To improve the linearity of the variable gain amplifier, when the input signal swing is too large, 2R S It can absorb part of the voltage drop, preventing the input tube from entering the nonlinear region.

[0034] It is understood that the present invention has been described through some embodiments, and those skilled in the art will recognize that various changes or equivalent substitutions can be made to these features and embodiments without departing from the spirit and scope of the invention. Furthermore, under the teachings of the present invention, these features and embodiments can be modified to adapt to specific situations and materials without departing from the spirit and scope of the invention. Therefore, the present invention is not limited to the specific embodiments disclosed herein, and all embodiments falling within the scope of the claims of this application are within the protection scope of the present invention.

Claims

1. A transimpedance amplifier that employs external control to reduce the settling time of a burst-mode optical receiver, characterized in that, It includes an external control pin VC, a gain control signal generation unit, a transimpedance amplifier, and a variable gain amplifier controlled by an analog voltage. The external control pin VC is an external control signal input port. After being output by the gain control signal generation unit, it is converted into a first gain control signal VC1, which is sent to the transimpedance amplifier, and a second gain control signal VC2, which is sent to the variable gain amplifier, to realize gain control. The gain control signal generation unit includes a comparator and a subtractor; the output of the comparator is connected to both the gain control port of the transimpedance amplifier and the input of the subtractor, and the output of the subtractor is connected to the port of the first gain control signal VC1 of the variable gain amplifier.

2. The transimpedance amplifier for reducing the settling time of a burst-mode optical receiver using external control as described in claim 1, characterized in that, The variable gain amplifier shown is based on the Gilbert unit current rudder type.

3. The transimpedance amplifier for reducing the settling time of a burst-mode optical receiver using external control as described in claim 2, characterized in that, The variable gain amplifier includes a first amplifier tube M1, a second amplifier tube M2, a third amplifier tube M3, a fourth amplifier tube M4, a fifth amplifier tube M5, a sixth amplifier tube M6, a first current mirror tube M7, a second current mirror tube M8, and a load resistor R. L The first amplifying transistor M1 and the second amplifying transistor M2 serve as amplifying transistors for the input signal. The source terminal of the first amplifying transistor M1 is connected to the drain terminal of the first current mirror transistor M7, the source terminal of the second amplifying transistor M2 is connected to the drain terminal of the second current mirror transistor M8, the drain terminal of the first amplifying transistor M1 is connected to the source terminals of the third amplifying transistor M3 and the fourth amplifying transistor M4, and the drain terminal of the second amplifying transistor M2 is connected to the source terminals of the fifth amplifying transistor M5 and the sixth amplifying transistor M6. The load resistor R... L Connect the drain terminals of the third amplifier transistor M3 and the sixth amplifier transistor M6, the drain terminals of the fourth amplifier transistor M4 and the fifth amplifier transistor M5, and the load resistor R. L The other end is connected to the power supply voltage VDD.

4. The transimpedance amplifier for reducing the settling time of a burst-mode optical receiver using external control as described in claim 2, characterized in that, The variable gain amplifier also includes a source degradation resistor 2R. S .

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