A control signal generating circuit, automatic gain control loop and TIA

Abstract

An embodiment of the present application discloses a control signal generating circuit, an automatic gain control loop, and a transimpedance amplifier (TIA), wherein the control signal generating circuit includes: a voltage-current conversion circuit, a current comparison circuit, and a voltage generating circuit; wherein the voltage-current conversion circuit is used to convert an input voltage signal to be controlled into its corresponding current signal to be controlled, and to convert an input reference voltage signal into its corresponding reference current signal; the current comparison circuit is used to compare the generated current signal to be controlled with the reference current signal to generate a difference current signal; and the voltage generating circuit is used to generate a voltage control signal based on the difference current signal.

Description

Technical Field

[0001] The present application relates to the field of integrated circuit control, and in particular to a control signal generating circuit, an automatic gain control loop applied to a trans-impedance amplifier (TIA), and the TIA. Background Art

[0002] With the development of 5G technology, modern high-speed optical communication systems are increasingly demanding high-speed TIAs. TIA chips are typically connected to an on-chip photoconductive detector (PD) via wirebonding, amplifying the PD's output AC current and suppressing its output DC current. As the front end of an optical receiver, the TIA determines the performance of the entire receiving system.

[0003] The first stage of a TIA (Transistor Isolation and Acquisition) core amplifier converts the input current signal into a voltage signal. This stage requires providing the maximum possible gain while suppressing noise in the link. The second stage is a variable gain amplifier (VGA). The VGA not only needs to provide a certain gain within the link but also needs to adjust the overall link gain based on the different PD output currents (i.e., the TIA input currents) to control the output swing around a specific value. VGA control methods include manual gain control and automatic gain control. Manual gain control typically implements gain control by transmitting a control signal to the VGA control signal via a register. Existing automatic gain control detects the swing of the TIA's output signal and uses multi-stage operational amplifiers to compare the TIA's output signal with a reference signal. This generates a control signal that is applied to the VGA to achieve gain control. This control signal generation module not only takes up a large area, but also, due to the cascaded connection of multiple amplifiers, can easily cause instability in the control loop. There are two ways to generate a reference voltage: external input or internal generation. External input of the reference voltage requires additional PINs on the chip, which not only consumes additional area but also increases design complexity. Summary of the Invention

[0004] To solve the above technical problems, embodiments of the present application provide a control signal generating circuit, an automatic gain control loop, and a TIA.

[0005] The technical solution of the embodiment of the present application is implemented as follows:

[0006] In a first aspect, an embodiment of the present application provides a control signal generating circuit, comprising: a voltage-current conversion circuit, a current comparison circuit, and a voltage generating circuit; wherein,

[0007] The voltage-current conversion circuit is used to convert the input voltage signal to be controlled into its corresponding current signal to be controlled, and to convert the input reference voltage signal into its corresponding reference current signal;

[0008] The current comparison circuit is used to compare the generated current signal to be controlled with the reference current signal to generate a difference current signal;

[0009] The voltage generating circuit is configured to generate a voltage control signal based on the difference current signal.

[0010] In a second aspect, an embodiment of the present application provides a control signal generator, including the control signal generating circuit provided by any embodiment of the present application.

[0011] In a third aspect, an embodiment of the present application provides an automatic gain control loop for a TIA, comprising a control signal generator, an envelope detector, a first operational amplifier, and a second operational amplifier provided in any embodiment of the present application; wherein,

[0012] The envelope detector is configured to use the differential voltage output by the TIA as the input of the envelope detector, corresponding to the output DC voltage; and use the ideal output differential voltage of the TIA as the input of the envelope detector, corresponding to the output ideal voltage;

[0013] The first operational amplifier is configured to take the ideal voltage and the DC voltage as inputs of the first operational amplifier and output a voltage signal to be controlled accordingly;

[0014] The second operational amplifier is configured to use the two ideal voltages as inputs of the second operational amplifier and output a corresponding reference voltage signal;

[0015] The control signal generator is configured to take the voltage signal to be controlled and the reference voltage signal as inputs of the control signal generator, output a corresponding voltage control signal, and apply the voltage control signal to the VGA of the TIA.

[0016] In a fourth aspect, an embodiment of the present application provides a TIA, including the automatic gain control loop provided by any embodiment of the present application.

[0017] The embodiments of the present application have the following beneficial effects: the present application provides a control signal generating circuit, comprising: a voltage-current conversion circuit, a current comparison circuit, and a voltage generating circuit; wherein the voltage-current conversion circuit is used to convert an input voltage signal to be controlled into its corresponding current signal to be controlled, and to convert an input reference voltage signal into its corresponding reference current signal; the current comparison circuit is used to compare the generated current signal to be controlled with the reference current signal to generate a difference current signal; and the voltage generating circuit is used to generate a voltage control signal based on the difference current signal. Through the voltage-current conversion capability of the transistor itself and the subtraction effect of the current in the branch, the comparison function between the signal to be controlled and the reference signal is directly realized, avoiding the instability and design difficulties caused by the multi-stage amplifier and saving the extra area occupied by the multi-stage amplifier. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 This is a schematic diagram of a control signal generating circuit provided in an embodiment of the present application;

[0019] Figure 2 is a schematic diagram of a control signal generating circuit provided by another embodiment of the present application;

[0020] Figure 3 This is a schematic diagram of an automatic gain control loop applied to a TIA provided in an embodiment of the present application;

[0021] Figure 4 This is a TIA provided in an embodiment of the present application. DETAILED DESCRIPTION

[0022] The following will describe the technical solutions in the embodiments of this application in conjunction with the drawings in the embodiments of this application. Obviously, the described embodiments are part of the embodiments of this application, not all of the embodiments. Based on the embodiments in this application, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of this application.

[0023] It should be noted that in the embodiments of the present application, the term "and / or" is merely a description of the association relationship between associated objects, indicating that three relationships can exist. For example, A and / or B can represent three situations: A exists alone, A and B exist at the same time, and B exists alone. In addition, in the embodiments of the present application, the character " / " generally indicates that the associated objects are in an "or" relationship.

[0024] In the description of the embodiments of the present application, the term "corresponding" may indicate a direct or indirect correspondence between the two, or an association relationship between the two, or a relationship between indication and being indicated, configuration and being configured, etc.

[0025] In order to enable a more detailed understanding of the features and technical content of this application, the implementation of this application is described in detail below in conjunction with the accompanying drawings. The attached drawings are for reference only and are not used to limit this application.

[0026] Figure 1 A schematic diagram of a control signal generating circuit provided in an embodiment of the present application is shown in FIG. Figure 1 As shown, the control signal generating circuit includes a voltage-current conversion circuit 10, a current comparison circuit 11 and a voltage generating circuit 12; wherein,

[0027] The voltage-current conversion circuit 10 is used to convert the input voltage signal to be controlled into its corresponding current signal to be controlled, and to convert the input reference voltage signal into its corresponding reference current signal;

[0028] The current comparison circuit 11 is used to compare the generated current signal to be controlled with the reference current signal to generate a difference current signal;

[0029] The voltage generating circuit 12 is configured to generate a voltage control signal based on the differential current signal.

[0030] Here, the voltage signal to be controlled and the reference voltage signal are converted into their corresponding current signals to be controlled and reference current signals, respectively. The current signal to be controlled and the reference current signal are then compared to obtain a differential current signal, and the voltage control signal is generated based on the differential current signal. Compared to the traditional voltage comparison using a multi-stage amplifier, this current comparison is simpler and more stable to implement, avoiding the instability and design difficulties associated with multi-stage amplifiers and saving the additional area occupied by the multi-stage amplifiers.

[0031] In another embodiment of the present application, the voltage-current conversion circuit includes a first P-channel metal oxide semiconductor field effect transistor (Positive channel Metal Oxide Semiconductor, PMOS), a second PMOS transistor, a third PMOS transistor and a fourth PMOS transistor; wherein,

[0032] The gates of the first PMOS transistor and the second PMOS transistor are connected to the voltage signal to be controlled, the drain of the first PMOS transistor outputs a first current signal to be controlled, and the drain of the second PMOS transistor outputs a second current signal to be controlled, and the first current signal to be controlled and the second current signal to be controlled are the same;

[0033] The gates of the third PMOS transistor and the fourth PMOS transistor are connected to the reference voltage, the drain of the third PMOS transistor outputs a first reference current signal, and the drain of the fourth PMOS transistor outputs a second reference current signal, and the first reference current signal and the second reference current signal are the same.

[0034] Here, the voltage-current conversion capability of the PMOS tube itself is utilized to conveniently convert the voltage signal into its corresponding current signal.

[0035] In another embodiment of the present application, the current comparison circuit is used to:

[0036] Comparing the first current signal to be controlled with the first reference current signal to obtain a first difference current signal; and

[0037] The second current signal to be controlled is compared with the second reference current signal to obtain a second difference current signal.

[0038] Specifically, the first reference current signal is subtracted from the first current signal to be controlled to obtain a first difference current signal; and

[0039] The second reference current signal is subtracted from the second current signal to obtain a second difference current signal.

[0040] In another embodiment of the present application, the current comparison circuit includes a first circuit and a second circuit, the first circuit includes a first current mirror, a second current mirror, and a third current mirror, and the second circuit includes a fourth current mirror, a fifth current mirror, and a sixth current mirror; wherein,

[0041] In the first circuit, the first current signal to be controlled passes through the first current mirror and the second current mirror, and the first reference current signal passes through the third current mirror, so that the first current signal to be controlled and the first reference current signal are converted into the same branch for subtraction operation to generate a first difference current signal;

[0042] In the second circuit, the second reference current signal passes through the fourth current mirror and the fifth current mirror, and the first current signal to be controlled passes through the sixth current mirror, so that the second current signal to be controlled and the second reference current signal are converted into the same branch for subtraction operation to generate a second difference current signal.

[0043] Here, a current mirror is used to transfer the controlled current signal and the reference signal into the same current branch. According to Kirchhoff's law, the series current signals automatically undergo a subtraction operation, resulting in a first difference current signal and a second difference current signal. This subtraction effect of the current in the branch directly implements the "comparison" function, avoiding the instability and design difficulties associated with direct voltage comparison using a multi-stage amplifier, and saving the additional area occupied by the multi-stage amplifier.

[0044] In another embodiment of the present application, the voltage generating circuit is used to:

[0045] generating a first differential voltage signal and a second differential voltage signal based on the first differential current signal and the second differential current signal;

[0046] The first difference voltage signal and the second difference voltage signal constitute a differential control signal.

[0047] Specifically, the voltage generating circuit includes a first heterojunction bipolar transistor (HBT), a second HBT tube, a third HBT tube, a fourth HBT tube, a first resistor, and a second resistor, wherein:

[0048] The first HBT transistor, the second HBT transistor, and the first resistor are connected in series, and the third HBT transistor, the fourth HBT transistor, and the second resistor are connected in series. One end of the first resistor is connected to a power supply, and the other end is connected to the collector of the first HBT transistor. The emitter of the first HBT transistor is connected to the collector of the second HBT transistor, and the emitter of the second HBT transistor is grounded. One end of the second resistor is connected to the same power supply as the first resistor, and the other end is connected to the collector of the third HBT transistor. The emitter of the third HBT transistor is connected to the collector of the fourth HBT transistor, and the emitter of the fourth HBT transistor is connected to the same ground as the emitter of the second HBT transistor. The first difference current is connected to the emitter of the first HBT transistor, and the second difference current is connected to the emitter of the third HBT transistor. The bases of the first, second, third, and fourth HBT transistors all have bias voltages, which are equivalent to fixed current sources. Thus, the first differential current determines the current in the branch consisting of the first, second, and first resistors, thereby determining the voltage drop across the first resistor and the voltage at the connection between the first HBT transistor and the first resistor. The voltage at the connection between the first HBT transistor and the first resistor is the first differential voltage signal. Similarly, the second differential current determines the voltage drop across the second resistor and the voltage drop at the connection between the third HBT transistor and the second resistor. The voltage at the connection between the third HBT transistor and the second resistor is the second differential voltage signal. The first and second differential voltage signals constitute a differential control signal.

[0049] Based on this, in another embodiment of the present application, the voltage generating circuit includes an HBT tube and a resistor.

[0050] Another embodiment of the present application provides a control signal generator, wherein the control signal generator includes the control signal generating circuit provided by any one of the aforementioned embodiments.

[0051] Another embodiment of the present application provides an automatic gain control loop (AGC loop) applied to a TIA, the AGC loop comprising the control signal generator provided in the previous embodiment of the present application, a peak detector (PKD), a first operational amplifier (Opamp), and a second operational amplifier; wherein,

[0052] The envelope detector is configured to use the differential voltage output by the TIA as the input of the envelope detector, corresponding to the output DC voltage; and use the ideal output differential voltage of the TIA as the input of the envelope detector, corresponding to the output ideal voltage;

[0053] The first operational amplifier is configured to take the ideal voltage and the DC voltage as inputs of the first operational amplifier and output a voltage signal to be controlled accordingly;

[0054] The second operational amplifier is configured to use the two ideal voltages as inputs of the second operational amplifier and output a corresponding reference voltage signal;

[0055] The control signal generator is configured to take the voltage signal to be controlled and the reference voltage signal as inputs of the control signal generator, output a corresponding voltage control signal, and apply the voltage control signal to the VGA of the TIA.

[0056] Here, the ideal output differential voltage of the TIA is input into the envelope detector to obtain the ideal voltage, and then the reference voltage signal is obtained through the first operational amplifier. Compared with directly generating the reference voltage signal from the TIA, the implementation is less difficult. By adopting the automatic gain control loop provided in the embodiment of the present application, the voltage-current conversion capability of the transistor itself and the subtraction effect of the current in the branch are utilized to directly realize the comparison function between the signal to be controlled and the reference signal, avoiding the instability and design difficulties caused by the multi-stage amplifier and saving the additional on-chip area occupied by the multi-stage amplifier.

[0057] The entire AGC loop exhibits a low-pass frequency response characteristic, which prevents high-frequency signals from being fed back to the VGA circuit through the AGC_loop and causing unnecessary crosstalk.

[0058] Another embodiment of the present application provides a TIA, which includes any one of the automatic gain control loops provided in the aforementioned embodiments.

[0059] For ease of understanding, the control signal generating circuit, automatic gain control loop, and transimpedance amplifier provided in this application are explained in more detail below in conjunction with specific embodiments. It should be noted that the circuit composition of the control signal generating circuit, automatic gain control loop, and transimpedance amplifier in the specific embodiments of this application is not limited to the specific circuits in the embodiments of this application.

[0060] Figure 2 A circuit diagram of a control signal generating circuit provided in an embodiment of the present application is shown. Figure 2 In the circuit, the voltage signal to be controlled V_in is used as the gate input of the PMOS tube Q1, and the drain of the PMOS tube Q1 outputs the current signal to be controlled I_in1. The reference voltage signal V_ref is used as the gate input of the PMOS tube Q2, and the drain of the PMOS tube Q2 outputs the current signal to be controlled I_ref1. After the I_in1 passes through the current mirror C1 and the current mirror C2, and the I_ref1 passes through the current mirror C3, the I_in1 and I_ref1 are converted into the same branch. According to Kirchhoff's law, I_in1 and I_ref1 automatically perform a subtraction effect to obtain a first difference current I_ p, the reference voltage signal V_ref serves as the gate input of the PMOS transistor Q3, and the drain of the PMOS transistor Q3 outputs the current signal to be controlled I_ref2. The voltage signal to be controlled V_in serves as the gate input of the PMOS transistor Q4, and the drain of the PMOS transistor Q1 outputs the current signal to be controlled I_in2. The I_ref2 passes through the current mirrors C4 and C5. After the I_in2 passes through the current mirror C6, the I_in2 and I_ref2 are converted into the same branch. According to Kirchhoff's law, I_in2 and I_ref2 automatically perform a subtraction effect to obtain a second difference current I_n.

[0061] I_p is connected to the emitter of HBT transistor H1, and I_n is connected to the emitter of HBT transistor H3. The bases of HBT transistors H1 and H3 have the same bias voltage Vb1, and HBT transistors H2 and H4 have the same bias voltage Vb2. They are equivalent to fixed current sources. In this way, the current in the branch formed by HBT transistors H1, H2, and resistor R1 is determined by I_p, and thus by the voltage drop I_p across resistor R1. I_p determines the first voltage control signal Vctrl_p. Similarly, I_n determines the second control voltage signal Vctrl_n. Vctrl_p and Vctrl_n constitute a differential control signal.

[0062] Figure 3An automatic gain control loop for TIA is provided in an embodiment of the present application, such as Figure 3 As shown in the figure, Vctrl Generaton is a control signal generator provided in an embodiment of the present application, and the control signal generator includes a control signal generating circuit provided in any one of the embodiments of the present application.

[0063] Figure 3 The TIA's output differential voltages AGC_in_p and AGC_in_n serve as inputs to an envelope detector PKD. The envelope detector PKD outputs a DC voltage Vpkd corresponding to the input signal amplitude, which increases monotonically with the input signal amplitude. The ideal TIA output differential voltage serves as the input to the envelope detector PKD. In a preferred embodiment of the present application, the ideal TIA output differential voltage swing is 400mV. The envelope detector PKD outputs its corresponding voltage V1. Vpkd and V1 serve as inputs to a first operational amplifier, Opamp1, which outputs a voltage signal to be controlled, V_in. V1 serves as inputs to a second operational amplifier, Opamp2, which outputs a reference voltage signal, V_ref. V_in and V_ref serve as inputs to a control signal generator, Vctrl_Generating, which outputs control signals, Vctrl_p and Vctrl_n, that act on the TIA's VGA to achieve automatic gain control.

[0064] The entire AGC_loop exhibits a low-pass frequency response characteristic, which prevents high-frequency signals from being fed back to the VGA circuit through the AGC_loop and causing unnecessary crosstalk.

[0065] Figure 4 A TIA is provided in an embodiment of the present application, such as Figure 4 As shown, Figure 4 The automatic gain control loop includes any automatic gain control loop provided in the embodiments of the present application.

[0066] In the figure, the output signal RFIN_X of the PD serves as the input of the first-stage TIA core amplifier stage group. The first-stage TIA core amplifier stage group converts the input current signal into voltage signals TIA_OUT_N and TIA_OUT_P. The TIA_OUT_N and TIA_OUT_P serve as the input of the VGA. After VGA gain amplification, the output driver outputs the gain-amplified signal. The automatic gain control loop collects the signal output by the output driver. Based on the output signal of the output driver, the automatic gain control loop generates a control signal to act on the VGA to complete automatic gain control.

[0067] The DCOC module in the figure samples the DC level of the differential signal output by the gain amplifier module, and uses negative feedback technology to offset the DC level difference caused by the mismatch in the differential amplifier.

[0068] The above description is merely a specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any changes or substitutions that can be easily conceived by a person skilled in the art within the technical scope disclosed in the present invention should be included in the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be based on the scope of protection of the claims.

Claims

1. A control signal generating circuit, characterized in that: The control signal generating circuit includes: a voltage-current conversion circuit, a current comparison circuit and a voltage generating circuit; wherein, The voltage-current conversion circuit is used to convert the input voltage signal to be controlled into its corresponding current signal to be controlled, and to convert the input reference voltage signal into its corresponding reference current signal; The current comparison circuit is used to compare the generated current signal to be controlled with the reference current signal to generate a difference current signal; The voltage generating circuit is used to generate a voltage control signal based on the difference current signal; wherein, The voltage-current conversion circuit includes a first PMOS transistor, a second PMOS transistor, a third PMOS transistor and a fourth PMOS transistor; wherein, The gates of the first PMOS transistor and the second PMOS transistor are connected to the voltage signal to be controlled, the drain of the first PMOS transistor outputs a first current signal to be controlled, and the drain of the second PMOS transistor outputs a second current signal to be controlled, and the first current signal to be controlled and the second current signal to be controlled are the same; The gates of the third PMOS transistor and the fourth PMOS transistor are connected to the reference voltage, the drain of the third PMOS transistor outputs a first reference current signal, and the drain of the fourth PMOS transistor outputs a second reference current signal, and the first reference current signal and the second reference current signal are the same.

2. The control signal generating circuit according to claim 1, wherein: The voltage generating circuit includes a heterojunction bipolar transistor (HBT) and a resistor.

3. The control signal generating circuit according to claim 1, wherein: The current comparison circuit is specifically used for: Comparing the first current signal to be controlled with the first reference current signal to obtain a first difference current signal; and The second current signal to be controlled is compared with the second reference current signal to obtain a second difference current signal.

4. The control signal generating circuit according to claim 3, wherein: The current comparison circuit is specifically used for: Subtracting the first reference current signal from the first current signal to be controlled to obtain a first difference current signal; and The second reference current signal is subtracted from the second current signal to obtain a second difference current signal.

5. The control signal generating circuit according to claim 4, wherein: The current comparison circuit includes a first circuit and a second circuit, the first circuit includes a first current mirror, a second current mirror and a third current mirror, and the second circuit includes a fourth current mirror, a fifth current mirror and a sixth current mirror; wherein, In the first circuit, the first current signal to be controlled passes through the first current mirror and the second current mirror, and the first reference current signal passes through the third current mirror, so that the first current signal to be controlled and the first reference current signal are converted into the same branch for subtraction operation to generate a first difference current signal; In the second circuit, the second reference current signal passes through the fourth current mirror and the fifth current mirror, and the first current signal to be controlled passes through the sixth current mirror, so that the second current signal to be controlled and the second reference current signal are converted into the same branch for subtraction operation to generate a second difference current signal.

6. The control signal generating circuit according to claim 5, wherein: The voltage generating circuit is specifically used to: generating a first differential voltage signal and a second differential voltage signal based on the first differential current signal and the second differential current signal; The first difference voltage signal and the second difference voltage signal constitute a differential control signal.

7. A control signal generator, characterized in that: The control signal generator includes the control signal generating circuit according to any one of claims 1 to 6.

8. An automatic gain control loop applied to a transimpedance amplifier (TIA), characterized in that: The automatic gain control loop comprises the control signal generator, envelope detector, first operational amplifier and second operational amplifier according to claim 7; wherein, The envelope detector is configured to use the differential voltage output by the TIA as the input of the envelope detector, corresponding to the output DC voltage; and use the ideal output differential voltage of the TIA as the input of the envelope detector, corresponding to the output ideal voltage; The first operational amplifier is configured to take the ideal voltage and the DC voltage as inputs of the first operational amplifier and output a voltage signal to be controlled accordingly; The second operational amplifier is configured to use the two ideal voltages as inputs of the second operational amplifier and output a corresponding reference voltage signal; The control signal generator is used to take the voltage signal to be controlled and the reference voltage signal as inputs of the control signal generator, output a corresponding voltage control signal and apply the voltage control signal to the variable gain amplifier VGA of the TIA.

9. A transimpedance amplifier (TIA), characterized in that: The TIA includes the automatic gain control loop as claimed in claim 8.

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