An analog front-end input matching circuit with bandwidth expansion function

Abstract

The present invention discloses an analog front-end input matching circuit with a bandwidth expansion function, which includes an input pad, a first electrostatic protection module, a second electrostatic protection module, a one-to-two differential transmission line, a first expansion module, and a second expansion module. The signal is input from the pad, and the ESD electrostatic protection module prevents static electricity from damaging the circuit; the impedance matching of the electrostatic protection module adopts a simplified T-coil structure to process the ESD capacitance, achieve impedance matching and expand the bandwidth; the one-to-two differential transmission line sends the signal to the input port, and its characteristic impedance matches the signal input; the expansion module adopts a simplified T-coil structure to process the load circuit capacitance, achieve impedance matching and expand the bandwidth; the termination resistor adopts an adjustable resistor structure and can be well terminated with the transmission line at different process corners and temperatures. This matching circuit has good bandwidth expansion and impedance matching effects, meeting the requirements of high-speed communication systems.

Description

Technical Field

[0001] The invention relates to high-speed analog front-end applications, and in particular to an analog front-end input matching circuit with a bandwidth expansion function. Background Art

[0002] With the reduction in the size of MOS devices and the increase in the operating speed of semiconductor integrated circuits, electrostatic discharge (ESD) circuits have received more and more attention. The operating speed of high-speed circuits has reached tens or even hundreds of GHz, and the requirements of high-speed circuits for ESD are becoming more and more stringent.

[0003] The input node parasitic capacitance mainly comes from the ESD circuit. In order to meet the protection standards, the ESD discharge capacitance value should not be designed to be too small, which will bring about a large amount of ESD parasitic capacitance, generally up to hundreds of fF or even larger, which is very unfavorable to the input bandwidth. In addition, during the layout implementation process, the parasitic capacitance of the pad, metal interconnection line and front-end circuit will also have an adverse effect on the bandwidth of the circuit.

[0004] In order to meet the requirements of high-speed circuit applications, input signals are often divided into multiple paths by transmission lines and sent to the input circuit. In addition, ideally, the output impedance of the source circuit is conjugate symmetrical with the input impedance of the load circuit, so the two-stage circuit can achieve perfect impedance matching, at which time signal reflection is suppressed to the greatest extent and transmission efficiency is maximized.

[0005] However, since parasitic capacitance is everywhere, when the signal source is connected to the input of the analog front end, the ideal matching state is no longer maintained. The signal transmission from the signal source is mainly affected by two parts of parasitic capacitance. The ESD circuit parasitic capacitance and the near-end input of the transmission line are connected in parallel, resulting in a large change in input impedance with frequency, making it impossible to achieve broadband impedance matching; the input capacitance of the input circuit and the output of the termination resistor are connected in parallel, resulting in a large change in output impedance with frequency, which is not matched with the impedance at the far end of the transmission line, resulting in reflection and signal attenuation. Even if the chip package is designed to have an ideal 50Ω transmission line, the on-chip capacitance of hundreds of fF may cause the broadband range to fail to meet the return loss requirements.

[0006] The T-coil circuit can be used to reduce the high-frequency signal loss caused by the ESD capacitive load and compensate for the impedance variation with frequency caused by the capacitor. In addition, the two coupled inductors can also provide ESD protection for the internal circuit transistors. Similarly, the T-coil can compensate for the bandwidth of the input capacitance of the input circuit, so as to ensure that the analog front end can maintain the signal amplitude within the required frequency range and achieve broadband impedance matching with the far end of the transmission line. Therefore, a multi-stage T-coil structure is required. However, the multi-stage T-coil structure achieves the purpose of bandwidth compensation for multiple capacitors at the cost of increasing the number of inductors. In addition, the impedance matching network based on the T-coil can transfer the signal to the backend circuit with the maximum gain. During the transfer process, the reasonable matching between impedances is an important condition to ensure smooth transmission. Therefore, impedance matching is also particularly important in the design considerations. Summary of the Invention

[0007] The technical problem to be solved by the present invention is aimed at the influence of the electrostatic protection ESD circuit capacitor C esd and the circuit input capacitor C L on the bandwidth and impedance matching of the analog front-end circuit, and provides an analog front-end input matching circuit with a bandwidth expansion function, and realizes the invention purpose of bandwidth expansion and impedance matching through a simplified T-coil technology, and solves the technical problems of bandwidth attenuation and impedance mismatch caused by multiple capacitors in the existing analog front-end.

[0008] The present invention adopts the following technical solutions to solve the above technical problems:

[0009] An analog front-end input matching circuit with a bandwidth expansion function includes a first to second electrostatic protection module, a one-to-two differential transmission line, and a first to second expansion module;

[0010] The circuit structures of the first electrostatic protection module and the second electrostatic protection module are the same, and both include an input pad, a first to second electrostatic protection transistors, and a first to second matching inductors. Among them, the first matching inductor and the second matching inductor are mutually inductive; the same-named end of the first matching inductor is connected to the input pad, and the different-named ends are respectively connected to the same-named end of the second matching inductor, one end of the first electrostatic protection transistor, and one end of the second electrostatic protection transistor; the other end of the first electrostatic protection transistor is connected to Vdd, and the other end of the second electrostatic protection transistor is grounded;

[0011] The input pad of the first electrostatic protection module is connected to a positive-polarity input signal, and the input pad of the second electrostatic protection module is connected to a negative-polarity input signal;

[0012] The one-to-two differential transmission line includes a first to a second input terminal and a first to a fourth output terminal. Among them, the first input terminal corresponds to the first output terminal and the third output terminal, and the second input terminal corresponds to the second output terminal and the fourth output terminal;

[0013] The first and second input terminals of the one-to-two differential transmission line are respectively connected to the other ends of the second matching inductors of the first and second electrostatic protection modules;

[0014] The circuit structures of the first expansion module and the second expansion module are the same, and both include a first to a fourth expansion inductor, a first to a second terminal resistor, and a common-mode level. Among them, the first and second expansion inductors are mutually inductive, the third and fourth expansion inductors are mutually inductive, and the mutual inductance coefficient of the first and second expansion inductors is equal to the mutual inductance coefficient of the third and fourth expansion inductors; the first and fourth expansion inductors have equal inductance values, and the second and third expansion inductors have equal inductance values; the resistance values of the first and second terminal resistors are equal; the different-named ends of the first expansion inductor and the same-named ends of the second expansion inductor are connected, the different-named ends of the second expansion inductor and one end of the first terminal resistor are connected, and the other end of the first terminal resistor is respectively connected to one end of the second terminal resistor and the common-mode level; the other end of the second terminal resistor is connected to the different-named end of the third expansion inductor, and the same-named end of the third expansion inductor is connected to the different-named end of the fourth expansion inductor; the different-named ends of the first expansion inductor and the different-named ends of the fourth expansion inductor are used as the input ports of the load circuit to be matched;

[0015] The first output terminal of the one-to-two differential transmission line is connected to the same-named end of the first expansion inductor in the first expansion module, the second output terminal is connected to the same-named end of the fourth expansion inductor in the first expansion module, the third output terminal is connected to the same-named end of the first expansion inductor in the second expansion module, and the fourth output terminal is connected to the same-named end of the fourth expansion inductor in the second expansion module.

[0016] Compared with the prior art, the present invention adopts the above technical solutions and has the following technical effects:

[0017] The present invention adopts a simplified T-coil structure to design a bandwidth expansion module, and at the same time endows it with an impedance matching function, realizing impedance matching of the analog front end while compensating for the multi-capacitance bandwidth. Compared with the analog front-end circuit that uses a multi-stage LC network for impedance matching and bandwidth expansion, the circuit proposed by the present invention greatly reduces the number of inductors and capacitors, thereby reducing the area overhead and circuit complexity. It has the technical advantages of good bandwidth expansion, good impedance matching, and strong engineering practicability, and can be widely used in the design of high-speed analog front ends, which can greatly improve the performance indicators of the analog front end. Description of the Drawings

[0018] Figure 1 It is a structural diagram of an analog front-end impedance matching circuit with a bandwidth expansion function proposed by the present invention;

[0019] Figure 2 is the circuit structure diagram of a conventional T - coil;

[0020] Figure 3 is the circuit structure diagram of a simplified T - coil;

[0021] Figure 4 is the structure diagram of a one - to - two differential transmission line in the present invention;

[0022] Figure 5 is the detailed circuit structure diagram of the electrostatic protection module in the present invention;

[0023] Figure 6 is the detailed circuit structure diagram of the expansion module in the present invention. Detailed implementation manners

[0024] The technical solution of the present invention will be further described in detail below with reference to the accompanying drawings:

[0025] The present invention can be implemented in many different forms and should not be considered limited to the embodiments described herein. On the contrary, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the present invention to those skilled in the art. In the drawings, components are enlarged for clarity.

[0026] It should be understood that although the terms first, second, third, etc. may be used herein to describe various elements, components, and / or parts, these elements, components, and / or parts are not limited by these terms. These terms are only used to distinguish one element, component, and / or part from another. Thus, the first element, component, and / or part discussed below may become the second element, component, or part without departing from the teachings of the present invention.

[0027] An analog front - end input matching circuit with a bandwidth expansion function disclosed by the present invention is as Figure 1 shown, including: a first input pad INP, a second input pad INN, a first electrostatic protection module IM1_1, a second electrostatic protection module IM1_2, a one - to - two differential transmission line 1 to 2 Differential Transmission Line, a first expansion module, a second expansion module, load circuits Input Buffer1, Input Buffer2.

[0028] The circuit structures of the first electrostatic protection module and the second electrostatic protection module are the same, and both include an input pad, first to second electrostatic protection transistors, and first to second matching inductors. Among them, the first matching inductor and the second matching inductor have mutual inductance; the same-named end of the first matching inductor is connected to the input pad, and the different-named ends are respectively connected to the same-named end of the second matching inductor, one end of the first electrostatic protection transistor, and one end of the second electrostatic protection transistor; the other end of the first electrostatic protection transistor is connected to Vdd, and the other end of the second electrostatic protection transistor is grounded;

[0029] The input pad of the first electrostatic protection module is connected to a positive-polarity input signal, and the input pad of the second electrostatic protection module is connected to a negative-polarity input signal;

[0030] The one-to-two differential transmission line includes first to second input terminals and first to fourth output terminals. Among them, the first input terminal corresponds to the first output terminal and the third output terminal, and the second input terminal corresponds to the second output terminal and the fourth output terminal;

[0031] The first and second input terminals of the one-to-two differential transmission line are respectively connected to the other ends of the second matching inductors of the first and second electrostatic protection modules;

[0032] The circuit structures of the first expansion module and the second expansion module are the same, and both include first to fourth expansion inductors, first to second terminal resistors, and a common-mode level. Among them, the first and second expansion inductors have mutual inductance, the third and fourth expansion inductors have mutual inductance, and the mutual inductance coefficient of the first and second expansion inductors is equal to the mutual inductance coefficient of the third and fourth expansion inductors; the inductance values of the first and fourth expansion inductors are equal, and the inductance values of the second and third expansion inductors are equal; the resistance values of the first and second terminal resistors are equal; the different-named end of the first expansion inductor and the same-named end of the second expansion inductor are connected, the different-named end of the second expansion inductor and one end of the first terminal resistor are connected, and the other end of the first terminal resistor is respectively connected to one end of the second terminal resistor and the common-mode level; the other end of the second terminal resistor is connected to the different-named end of the third expansion inductor, and the same-named end of the third expansion inductor is connected to the different-named end of the fourth expansion inductor; the different-named ends of the first expansion inductor and the fourth expansion inductor are used as the input ports of the load circuit to be matched;

[0033] The first output terminal of the one-to-two differential transmission line is connected to the same-named end of the first expansion inductor in the first expansion module, the second output terminal is connected to the same-named end of the fourth expansion inductor in the first expansion module, the third output terminal is connected to the same-named end of the first expansion inductor in the second expansion module, and the fourth output terminal is connected to the same-named end of the fourth expansion inductor in the second expansion module.

[0034] Figure 1In the first electrostatic protection module IM1_1, the input pad is INP, the first and second electrostatic protection transistors are ESD1_N and ESD1_P respectively, and the first and second matching inductors are L T1P_1 and L T1P_2 ; in the second electrostatic protection module IM1_2, the input pad is INN, the first and second electrostatic protection transistors are ESD2_N and ESD2_P respectively, and the first and second matching inductors are L T1N_1 and L T1N_2 ; in the first expansion module, the first to fourth expansion inductors are L T2P_1 and L T2P_2 and L T2N_2 and L T2N_1 , the first to second terminal resistors are R T1P and L T1N , the common-mode level is VCM, and the load circuit is InputBuffer1; in the second expansion module, the first to fourth expansion inductors are L T2P_3 and L T2P_4 and L T2N_4 and L T2N_3 , the first to second terminal resistors are R T2P and L T2N , the common-mode level is VCM, and the load circuit is InputBuffer2.

[0035] Since IM1_1 and IM1_2 are exactly the same, IM1_1 will be taken as an example for explanation later.

[0036] To solve the problems of bandwidth attenuation and impedance variation caused by multiple parasitic capacitances, based on the T-coil structure, bandwidth expansion and impedance matching circuit designs are respectively carried out before and after the one-to-two differential transmission line, and it is simplified to reduce the circuit overhead area.

[0037] The proposed analog front-end impedance matching circuit with bandwidth expansion function is implemented as follows.

[0038] According to the actual circuit, the basic circuit parameters are determined. Due to the existence of multiple-node parasitic capacitances, two-stage bandwidth expansion and impedance matching modules are required, and finally two T-coil structures are determined. The T-coil structure is as Figure 2 shown. According to the parasitic capacitance and the characteristic impedance of the transmission line, the parameters of the inductance, coupling coefficient, and bridging capacitance in the T-coil are calculated and determined. Since the magnitude of the bridging capacitance is very small and there is parasitic capacitance between the two inductors in the actual circuit implementation, the bridging capacitance is omitted in the actual circuit. The simplified T-coil is as Figure 3 shown. The one-to-two differential transmission line structure is as Figure 4 shown. The circuit details of the first electrostatic protection module are as Figure 5As shown, the circuit details of the first expansion module are as Figure 6 shown. Through full circuit simulation, parameter optimization is carried out for the simulation results. Process corner, temperature, and power supply voltage variation simulations are performed to determine the adjustment range of the adjustable termination resistor.

[0039] Please refer to Figure 1 , the present invention provides an analog front-end terminal circuit with bandwidth expansion and impedance matching functions. First, regarding the capacitance C esd of the electrostatic protection ESD_P transistor and the single-ended input capacitance C L of the Input Buffer1 in the load circuit, the influence of these two capacitances on the bandwidth and impedance matching of the analog front-end circuit is considered, and the capacitance parameters of the actual designed circuit are obtained. As Figure 2 shown, the method of bandwidth expansion is mainly based on the T-coil. The bandwidth expansion effect is quantified by the bandwidth expansion ratio (BWER). Under specific conditions, the BWER can be as high as 2.83. Under ideal conditions, when achieving this bandwidth expansion effect, the impedance seen from the input end of the T-coil is R T , and the capacitance C P has been completely shielded under the action of the inductor and the bridging capacitance. Therefore, the T-coil also exhibits good performance in terms of impedance matching. According to the above analysis, the parameters of the two-stage T-coil structure can be obtained from the known conditions. After obtaining the inductance, coupling coefficient, and the parameters of the bridging capacitance of the T-coil structure corresponding to each capacitance, the T-coil structure formed by the capacitance C esd of the electrostatic protection ESD circuit is placed in the first stage, and the first-stage T-coil is terminated with the proximal end of the one-to-two differential transmission line; the T-coil structure formed by the capacitance C L of the load circuit is placed in the second stage, and the input of the second-stage T-coil structure is connected to the distal end of the one-to-two differential transmission line and terminated with an adjustable termination resistor. Since the capacitance value of the bridging capacitance of the T-coil structure is very small itself, and considering the existence of parasitic capacitance in the actual inductor, the bridging capacitance C B is directly omitted.

[0040] In summary, an analog front-end input matching circuit with a bandwidth expansion function proposed by the present invention can greatly compensate for the bandwidth attenuation caused by capacitance, expand the bandwidth, and achieve a good impedance matching effect.

[0041] Those skilled in the art can understand that, unless otherwise defined, all terms used herein (including technical and scientific terms) have the same meaning as the general understanding of those of ordinary skill in the art to which this invention pertains. It should also be understood that terms such as those defined in a general dictionary should be understood to have a meaning consistent with their meaning in the context of the prior art, and will not be interpreted in an idealized or overly formal sense unless defined as such herein.

[0042] The specific embodiments described above further elaborate on the purpose, technical solutions, and beneficial effects of the present invention. It should be understood that the above description is only for the specific embodiments of the present invention and is not intended to limit the present invention. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principles of the present invention shall be included within the protection scope of the present invention.

Claims

1. An analog front-end input matching circuit with bandwidth expansion function, characterized in that It includes a first to a second electrostatic protection module, a one-to-two differential transmission line, and a first to a second expansion module; The circuit structures of the first electrostatic protection module and the second electrostatic protection module are the same, and both include an input pad, a first to a second electrostatic protection transistor, and a first to a second matching inductor. Among them, the first matching inductor and the second matching inductor have mutual inductance; the same-named end of the first matching inductor is connected to the input pad, and the different-named ends are respectively connected to the same-named end of the second matching inductor, one end of the first electrostatic protection transistor, and one end of the second electrostatic protection transistor; the other end of the first electrostatic protection transistor is connected to Vdd, and the other end of the second electrostatic protection transistor is grounded; The input pad of the first electrostatic protection module is connected to a positive-polarity input signal, and the input pad of the second electrostatic protection module is connected to a negative-polarity input signal; The one-to-two differential transmission line includes a first to a second input end and a first to a fourth output end. Among them, the first input end corresponds to the first output end and the third output end, and the second input end corresponds to the second output end and the fourth output end; The first and second input ends of the one-to-two differential transmission line are respectively connected to the other ends of the second matching inductors of the first and second electrostatic protection modules; The circuit structures of the first expansion module and the second expansion module are the same, and both include a first to a fourth expansion inductor, a first to a second terminal resistor, and a common-mode level. Among them, the first and second expansion inductors have mutual inductance, the third and fourth expansion inductors have mutual inductance, and the mutual inductance coefficient of the first and second expansion inductors is equal to the mutual inductance coefficient of the third and fourth expansion inductors; the inductance values of the first and fourth expansion inductors are equal, and the inductance values of the second and third expansion inductors are equal; the resistance values of the first and second terminal resistors are equal; the different-named end of the first expansion inductor and the same-named end of the second expansion inductor are connected, the different-named end of the second expansion inductor and one end of the first terminal resistor are connected, and the other end of the first terminal resistor is respectively connected to one end of the second terminal resistor and the common-mode level; the other end of the second terminal resistor is connected to the different-named end of the third expansion inductor, and the same-named end of the third expansion inductor is connected to the different-named end of the fourth expansion inductor; the different-named ends of the first expansion inductor and the fourth expansion inductor are used as the input ports of the load circuit to be matched; The first output end of the one-to-two differential transmission line is connected to the same-named end of the first expansion inductor in the first expansion module, the second output end is connected to the same-named end of the fourth expansion inductor in the first expansion module, the third output end is connected to the same-named end of the first expansion inductor in the second expansion module, and the fourth output end is connected to the same-named end of the fourth expansion inductor in the second expansion module.

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