CPO Module

Abstract

To provide a variable output impedance driver circuit, a laser driver circuit, and a CPO module that can support the multi-channel of a CPO (Co-Packaged Optics) module, and suppress the deterioration of communication quality for design errors during manufacturing or PVT variations in the laser driver circuit.SOLUTION: A variable output impedance driver circuit 40 includes a differential signal input unit 41 and an output circuit unit 42 that outputs a differential amplified signal. The output circuit unit 42 is configured to be able to control output impedance.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present invention relates to a variable output impedance driver circuit, a laser driver circuit, and a CPO module. [Background technology]

[0002] Cyber-physical systems (CPS), which transmit large-scale data in the real world via high-speed networks and perform large-scale data processing in cyberspace, are attracting attention, and there is a growing demand for even faster and higher-capacity optical communication systems within data centers.

[0003] Due to limitations in the high-frequency operation of integrated circuits, increasing the transmission rate per channel is difficult. Therefore, multi-channel transmission using multi-core fibers, which integrate multiple optical cores into a single fiber, has been proposed. As a technology to realize this, Co-Packaged Optics (CPO), which combines multiple optical devices, integrated circuits, and switch ASICs into a single package to reduce power consumption, improve thermal efficiency, and miniaturize the device, is considered a promising solution.

[0004] In CPO modules, the laser diode (LD) and laser driver circuit (LDD) are wired together via an interposer. Challenges include increased wiring length due to multi-channel operation and degradation of communication quality due to higher signal speeds.

[0005] Degradation of communication quality is caused by reflected waves resulting from mismatches between input / output impedance and the characteristic impedance of the wiring. Patent Document 1 describes a laser driver circuit that includes a resistor in series with a pair of transistors in a differential configuration for impedance matching in order to suppress the generation of reflected waves. Patent Document 2 describes an optical / electrical conversion module that includes a termination resistor for impedance matching of an optical element with components outside the package. [Prior art documents] [Patent Documents]

[0006] [Patent Document 1] Japanese Patent Application Laid-Open No. 2004-363360 [Patent Document 2] Japanese Patent Application Laid-Open No. 2005-167189 [Summary of the Invention] [Problems to be Solved by the Invention]

[0007] The impedance matching methods described in Patent Documents 1 and 2 both use fixed resistors. However, in order to accommodate the multi-channeling of the CPO module, the physical structure of each channel between a large number of laser diodes and laser driver circuits becomes non-identical, or electromagnetic field coupling occurs between channels due to the proximity of high-frequency signals, resulting in different characteristic impedances for each channel. Therefore, it is difficult to handle this with fixed resistors. Also, design errors during the manufacture of the CPO module and variations in the PVT (Process-Voltage-Temperature) of the laser driver circuit etc. also become factors that deviate from the impedance matching conditions.

[0008] An object of the present invention is to provide an output impedance variable driver circuit, a laser driver circuit, and a CPO module that can accommodate multi-channeling in a CPO module and suppress deterioration of communication quality against design errors during manufacture or variations in the PVT of the laser driver circuit. [Means for Solving the Problems]

[0009] The output impedance variable driver circuit according to the present invention includes a differential signal input section And, and an output circuit section that outputs a width signal, and the output circuit section is configured to be able to control the output impedance.

[0010] With the above configuration, the output impedance of the driver circuit can be varied, making it possible to adjust the output impedance of the driver circuit to the characteristic impedance of the wiring even after the circuit has been implemented, thus realizing a driver circuit that is less affected by reflected waves in the signal.

[0011] In the output impedance variable driver circuit according to the present invention, the output circuit section preferably has a transistor with one end connected to a control power supply and equipped with a control terminal, and the impedance of the transistor is changed by controlling at least one of the voltage of the control power supply and the voltage applied to the control terminal of the transistor.

[0012] With the above configuration, by using a transistor as an active element, the output impedance of the driver circuit can be easily changed by voltage control.

[0013] In the output impedance variable driver circuit according to the present invention, the differential signal input section has a differential pair of a first n-MOSFET and a second n-MOSFET, the source terminal of the first n-MOSFET and the source terminal of the second n-MOSFET are connected to a current source having a third n-MOSFET, and the transistor in the output circuit section is preferably a p-MOSFET.

[0014] With the above configuration, since the driver circuit is made up of MOSFETs, a driver circuit with low driving power and high efficiency can be realized.

[0015] The laser driver circuit according to the present invention is characterized by comprising a differential input type input buffer circuit, a waveform shaping circuit that receives the voltage output by the input buffer circuit, and an output impedance variable driver circuit that receives the voltage output by the waveform shaping circuit.

[0016] According to the above configuration, the output impedance can be adjusted to the characteristic impedance of the wiring after circuit implementation, thereby realizing a laser driver circuit that can suppress the degradation of communication quality.

[0017] The CPO module according to the present invention is a CPO module in which a laser driver circuit and a laser diode that receives the output current of the laser driver circuit are mounted on a substrate, characterized in that the output impedance of the output circuit portion of the laser driver circuit is impedance-matched with the characteristic impedance of the wiring between the laser driver circuit and the laser diode.

[0018] According to the above configuration, reflected waves can be suppressed in the laser driver circuit, and a CPO module capable of suppressing degradation of communication quality can be realized.

[0019] In the CPO module according to the present invention, it is preferable that the characteristic impedance of the wiring matches the input impedance of the laser diode.

[0020] With the above configuration, reflected waves from the laser diode to the laser driver circuit via wiring can be suppressed, and the operation of the laser driver circuit can be stabilized. [Effects of the Invention]

[0021] According to the output impedance variable driver circuit, laser driver circuit, and CPO module of the present invention, it is possible to support multi-channel operation and suppress the degradation of communication quality due to design errors during manufacturing or PVT variations of the LDD. [Brief explanation of the drawing]

[0022] [Figure 1] This is a basic circuit diagram of the laser driver circuit and laser diode included in the CPO module of an embodiment of the present invention. [Figure 2] This is a circuit diagram of a variable output impedance driver circuit according to the present invention. [Figure 3] This diagram illustrates impedance matching in a conventional driver circuit. [Figure 4] This diagram illustrates the impedance matching of the output impedance variable driver circuit of the present invention. [Figure 5] This figure illustrates the control effect of the output impedance of a variable output impedance driver circuit according to the present invention. [Modes for carrying out the invention]

[0023] Embodiments of the present invention will be described in detail below with reference to the drawings. In the following description, specific shapes, materials, directions, numerical values, etc., are examples to facilitate understanding of the present invention and can be appropriately modified according to the application, purpose, specifications, etc. Furthermore, it is intended from the outset that the components of the embodiments and modifications described below can be selectively combined.

[0024] Figure 1 shows the basic circuit 10 of the laser driver circuit LDD and laser diode LD included in the CPO (Co-Packaged Optics) module 1 of the present invention. The CPO module 1 is a module that realizes multi-channel optical transmission by implementing the basic circuit 10 shown in Figure 1 for each channel. In the basic circuit 10 of the CPO module 1 shown in Figure 1, the laser driver circuit LDD and the laser diode LD are connected by an interposer 11 which corresponds to electrical wiring.

[0025] The laser driver circuit LDD uses a differential voltage V INP , V INN When the input is given, the differential voltage V INP and V INN The voltage V is the amplified difference. OUT It outputs a current, which flows through the laser diode LD. The output current of the laser driver circuit LDD is transmitted to the laser diode LD via the interposer 11.

[0026] The interposer 11 is a substrate structure that electrically connects the output terminal of the laser driver circuit LDD and the anode terminal of the laser diode LD. The interposer 11 has a characteristic impedance Z0 in the signal frequency band output by the laser driver circuit LDD.

[0027] The laser diode LD emits light upon receiving the output current from the laser driver circuit LDD. In the CPO module 1, the laser diode LD blinks according to the modulated output current of the laser driver circuit LDD and transmits it as an optical signal to a subsequent optical fiber (not shown).

[0028] The details of the laser driver circuit LDD in FIG. 1 will be described. The laser driver circuit LDD has an input buffer circuit 20, a waveform shaping circuit 30, and an output impedance variable driver circuit 40 (hereinafter simply referred to as the driver circuit 40).

[0029] The input buffer circuit 20 has a non-inverting input terminal and an inverting input terminal. The external modulation signal is input to the non-inverting input terminal and the inverting input terminal of the input buffer circuit 20.

[0030] Voltage V INP is input to the non-inverting input terminal of the input buffer circuit 20. Voltage V INP and a voltage V INN with the opposite phase are input to the inverting input terminal. The input buffer circuit 20 outputs the amplified voltage of the difference between voltage V INP and V INN as a differential voltage.

[0031] The waveform shaping circuit 30 is a circuit that compensates for the deterioration of the voltage waveform output by the input buffer circuit 20. For example, the waveform shaping circuit 30 is composed of an FFE (Feed Forward Equalizer). However, the waveform shaping circuit 30 is not limited to FFE, and it may also be a CTLE (Continuous Time Linear Equalizer) or other configurations. Also, the waveform shaping circuit 30 is not an essential configuration and may be omitted.

[0032] The driver circuit 40 receives the differential voltage output by the waveform shaping circuit 30 and performs voltage / current conversion. The laser diode LD is driven by the modulated current signal output from the driver circuit 40. The laser diode LD emits light (blinks) according to the current signal and outputs an optical signal.

[0033] The electrical signal output by the laser driver circuit (LDD) is a high-frequency signal on the order of several GHz, enabling high-speed, high-capacity optical transmission. Therefore, the electrical signal transmitted from the laser driver circuit (LDD), which is the drive circuit for the laser diode (LD), to the interposer 11 is affected by reflected waves due to output impedance mismatch, leading to a deterioration in communication quality.

[0034] To address the degradation of communication quality due to impedance mismatch, it is necessary to perform impedance matching between the output impedance of the laser driver circuit LDD, the characteristic impedance of the interposer 11, and the input impedance of the laser diode LD.

[0035] Typically, impedance matching is performed by connecting a fixed resistor so that the output impedance or input impedance matches the characteristic impedance Z0 of the interposer 11. As mentioned earlier, the CPO module 1 has multiple basic circuits 10 as shown in Figure 1, and since the characteristic impedance value of the interposer between each laser driver circuit and laser diode differs for each channel, it is difficult to perform all impedance matching with a single fixed resistor. Furthermore, as stated in the problem, a fixed resistor cannot accommodate design errors during the manufacturing of the CPO module 1 or variations in the PVT (Process-Voltage-Temperature) of the LDD.

[0036] Next, Figure 2 shows the circuit configuration of the driver circuit 40 provided in the laser driver circuit LDD of the present invention. The driver circuit 40 has a differential voltage V INP ',V INN This circuit receives a signal, performs voltage / current conversion, and outputs a modulated current. The driver circuit 40 has a differential signal input section 41, an output circuit section 42, and a constant current section 43. The driver circuit 40 generates a bias current using the output circuit section 42 and outputs a modulated current to the laser diode by inputting a differential modulated signal to the differential signal input section 41.

[0037] The driver circuit 40 is composed of an n-MOSFET and a p-MOSFET. Specifically, the first transistor M N1 , the second transistor M N2 , the third transistor M N3 , the fourth transistor M P It is composed of the following. In Figure 2, the first to third transistors are composed of n-MOSFETs, and the fourth transistor M P It is composed of p-MOSFETs.

[0038] The differential signal input section 41 is connected to the first transistor M N1 and the second transistor M N2 It consists of the first transistor M of the differential signal input section 41. N1 The drain terminal is connected to the first power supply voltage V DDL When the current is applied, the source terminal is connected to the second transistor M N2 The source terminal and the drain terminal of the third transistor are connected, and the gate terminal is connected to the positive-sequence differential voltage V INP’ The following is input. The second transistor M of the differential signal input section 41 N2 The drain terminal is the 4 Transistor M P The drain terminal is connected to the first transistor M, and the source terminal is connected to the first transistor M. N1 The source terminal is connected to the drain terminal of the third transistor, and the gate terminal is connected to the differential voltage V in opposite phase. INN’ The following is entered.

[0039] The constant current section 43 controls the third transistor M N3 It is composed of the third transistor M of the constant current section 43. N3 The drain terminal of the third transistor M is connected to the source terminals of the first and second transistors. N3 The source terminal is connected to the circuit ground GND, and the gate terminal is connected to the bias voltage V NB The following is input. The constant current section 43 receives the bias voltage V NB By controlling this, it has the function of controlling the current flowing to the differential signal input section 41.

[0040] The output circuit section 42 has a fourth transistor M P It is composed of the fourth transistor M of the output circuit section 42 P The source terminal is connected to the second power supply voltage V DDH When a current is applied, the drain terminal is connected to the second transistor M N2 The drain terminal is connected, and the gate terminal is connected to the control voltage V PB The voltage is applied. As will be described later, the fourth transistor M P The control voltage V at the gate terminal PB , or the second power supply voltage V DDH By controlling the fourth transistor M P The internal resistance can be controlled.

[0041] Next, referring to Figures 3 and 4, the impedance matching of the laser driver circuit LDD will be explained. The following explanation assumes that the output impedance of the driver circuit 40 is matched to the characteristic impedance of the interposer 11.

[0042] Figure 3 is a circuit diagram of a driver circuit 40A that performs impedance matching using a conventional method. Components similar to those in the driver circuit 40 of Figure 2 are denoted by the same reference numerals, and detailed explanations are omitted. In the driver circuit 40A, the output circuit section 42 of the driver circuit 40 of Figure 2 is connected to a fixed resistor R OUT The configuration is the same except that (output circuit section 42A) has been replaced. The design value of the characteristic impedance of the interposer 11 is set to Z0. To match the output impedance with the characteristic impedance of the interposer 11 and achieve impedance matching, the second power supply voltage V DDH and output terminal V OUT Fixed resistor R between them OUTConnect the resistor (resistance value Z0). As already mentioned, in the CPO module 1, many basic circuits 10 consisting of a laser driver circuit LDD, an interposer 11, and a laser diode LD are implemented. The characteristic impedance of the interposer 11 is different for each of the basic circuits 10. Therefore, the resistance value for impedance matching will be different for each basic circuit 10. Also, in actual designs, the characteristic impedance Z0 of the interposer 11 may have design errors and may not match the resistance value Z0, thus deviating from the impedance matching conditions. However, the resistor R OUT Since it is a fixed resistor, the resistance value cannot be changed after the circuit is created. Furthermore, the characteristic impedance of the interposer 11 differs for each basic circuit 10, and the impedance matching conditions differ. Therefore, it is not easy to perform impedance matching of the electrical wiring in the CPO module 1 and suppress the degradation of communication quality.

[0043] To address this, it is necessary to make the output impedance of the laser driver circuit LDD variable after circuit implementation. As shown in Figure 4, the present invention provides a second power supply voltage V DDH and output terminal V OUT The output circuit section 42 between these components has a variable impedance configuration. This configuration allows for impedance matching by adjusting the output impedance even in cases of impedance mismatch due to design errors during manufacturing or PVT variations in the LDD after circuit implementation. Therefore, it is possible to suppress the degradation of the communication quality of the optical transmission of the CPO module 1.

[0044] Specifically, as shown in Figure 4, the output circuit section 42 is controlled by the second power supply voltage V as a means of varying the output impedance. DDH and output terminal V OUT The space between them is replaced with an active element such as a MOSFET. By controlling the gate voltage so that the MOSFET operates in the linear region, the internal resistance r of the MOSFET is reduced. outThe resistance value can be changed. This allows the output impedance to be adjusted and impedance matching to be achieved even if there are manufacturing tolerances in the characteristic impedance value of the interposer 11, or differences in the characteristic impedance value of the interposer 11 for each channel, thereby suppressing the effects of reflected waves.

[0045] In the driver circuit 40 of the present invention shown in Figure 2, the control voltage V PB By controlling the fourth transistor M P The internal impedance can be controlled, and the output impedance of the laser driver circuit LDD can be adjusted. Furthermore, the second power supply voltage V DDH By changing the value of, the fourth transistor M P The internal impedance can be changed.

[0046] The driver circuit 40 with the above configuration controls the second power supply voltage V DDH and control voltage V PB By controlling the fourth transistor M P The internal resistance value of the driver circuit 40 can be controlled to be variable. Therefore, it becomes possible to control the output impedance of the driver circuit 40 and, by matching it with the characteristic impedance of the interposer 11 connected to the subsequent stage, it becomes possible to suppress reflected waves. Furthermore, the laser driver circuit LDD having the driver circuit 40 can suppress the deterioration of the communication quality of optical transmission. In addition, it is preferable to design the characteristic impedance of the interposer 11 to match the input impedance of the laser diode LD. This suppresses reflected waves from the laser diode LD to the laser driver circuit LDD via the interposer 11, thereby stabilizing the operation of the laser driver circuit LDD.

[0047] Next, the controllability of the output impedance of the driver circuit 40 of the present invention will be explained with reference to Figure 5. Figure 5 shows the control voltage V PB This shows the output impedance when the value is changed.

[0048] Control voltage V PB When the voltage is varied from 0V to 0.5V, it can be confirmed that the output impedance changes from approximately 50Ω to approximately 90Ω. Since the interposer's characteristic impedance value is set to, for example, 50Ω, it can be seen that sufficient controllability is ensured to compensate for design errors and differences in characteristic impedance between multiple channels.

[0049] Therefore, impedance mismatches due to design errors and process variations can be compensated for by the control voltage, and consequently, degradation of signal quality in optical communication using the laser driver circuit LDD can be suppressed. Furthermore, by incorporating the driver circuit of the present invention, it is expected that the eye pattern of the output voltage waveform of the laser driver circuit LDD when a high-frequency signal is input will also be improved.

[0050] It should be noted that the present invention is not limited to the embodiments and their modifications described above, and various changes and improvements are possible within the scope of the claims of this application. [Explanation of Symbols]

[0051] 1 CPO module, 10 basic circuit, 11 interposer, 20 input buffer circuit, 30 waveform shaping circuit, 40, 40A variable output impedance driver circuit (driver circuit), 41 differential input section, 42, 42A output circuit section, 43 constant current section, LDD laser driver circuit, LD laser diode

Claims

1. A CPO (Co-Packaged Optics) module comprising a laser driver circuit and a laser diode mounted on a substrate, The aforementioned laser driver circuit is A differential signal input section formed by a differential pair, The output circuit section outputs an amplified signal, Equipped with, The output circuit section is, The differential pair has a transistor connected in series between its output terminals and the control power supply, and is equipped with a control terminal. This is a variable output impedance driver circuit configured to control the output impedance by changing the impedance of the transistor by controlling at least one of the voltage of the control power supply and the voltage applied to the control terminal of the transistor. A CPO module characterized by the following features.

2. The differential signal input section has a differential pair of first n-MOSFETs and second n-MOSFETs. The source terminal of the first n-MOSFET and the source terminal of the second n-MOSFET are connected to a current source having a third n-MOSFET. The transistor in the output circuit section is a p-MOSFET. The CPO module according to claim 1.

3. The laser driver circuit further comprises: A differential input type input buffer circuit, A waveform shaping circuit that receives the voltage output by the input buffer circuit, A CPO module according to claim 1 or 2, comprising:

4. The characteristic impedance of the wiring between the laser driver circuit and the laser diode matches the input impedance of the laser diode. A CPO module according to any one of claims 1 to 3.

5. Laser driver circuit and Laser diode and A CPO module comprising, The aforementioned laser driver circuit is Differential pair and, The differential pair has a transistor connected in series with the power supply, The output impedance is variable by changing the impedance of the transistor so that impedance matching can be performed to match the characteristic impedance of the wiring connecting the laser driver circuit and the laser diode. A CPO module characterized by the following.

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