Communication device, terminal device and active optical cable

Abstract

The communication device (111) is provided with a control section (10), a differential input terminal resistor (11), a linear laser driver (12), a transmission signal detection section (13), a linear trans-impedance amplifier (14), a linear variable gain amplifier (15), a linear output driver (16), a pulse number detection section (17), a reception signal detection section (18), and an amplitude detection section (19). The control section (10) outputs a Term signal for setting the resistance value of the differential input terminal resistor (11), a TxEN signal and an LS signal for controlling the operation of the linear laser driver (12), an RxEN signal for controlling the operation of the linear TIA (14), the linear VGA (15), and the linear output driver (16), and a GCTL signal for controlling the gain of the linear VGA (15).

Description

Technical Field

[0001] This invention relates to communication devices, terminal devices, and active optical cables. Background Technology

[0002] Universal Serial Bus (USB) is one of the serial bus standards used to connect peripheral devices to information devices such as computers. USB became the most prevalent universal interface standard for personal computer peripherals after USB 1.0, which appeared as the initial standard in 1996. The USB 3.2 standard was officially released in September 2017, and the USB 4 standard was officially released in August 2019. USB 4 requires backward compatibility with USB 3.2.

[0003] The data rate (per channel) of the SS (Super Speed) signal, which serves as the primary signal, is 5Gbps in USB 3.2 Gen1, 10Gbps in USB 3.2 Gen2, 10Gbps in USB 4 Gen2, and 20Gbps in USB 4 Gen3. The SS signal is a differential signal. Communication using the SS signal can utilize two channels.

[0004] Figure 1 This diagram illustrates the structure of two devices connected via a USB4-compliant communication cable. The DFP (Downstream Facing Port) and UFP (Upstream Facing Port) are the link components. The DFP is the host-side device, such as a computer or other information equipment. The UFP is the device-side device, such as a mouse, monitor, or other peripheral device. Lane adapters are located on both the DFP and UFP and are the main components for USB4-based SS signal communication. The DFP includes a Lane 0 adapter and a Lane 1 adapter. The UFP also has a Lane 0 adapter and a Lane 1 adapter. Lane 0 and Lane 1 are bonded. These USB channels can provide differential signal pairs for transmitting and receiving. Sidebands (SBCs) are two wire channels.

[0005] DFP and UFP are connected to each other via a communication cable. When the communication cable connecting the DFP and UFP is short, it can be a passive cable. However, when the communication cable is long (e.g., 0.8m or more in the case of USB4), it must be an active cable. Active cables include active copper cables (ACC) that maintain the electrical signal transmission and active optical cables (AOC) that convert electrical signals into optical signals and transmit them.

[0006] Active cables contain active devices. These active devices can actively respond to the main signal in accordance with power consumption. In the case of ACC (Adaptive Charge), active devices include re-drivers and re-timers that correct for signal loss (especially high-frequency band loss). In the case of AOC (Adaptive Charge), active devices include laser diodes that convert current signals to optical signals, laser drivers that supply current signals to drive laser diodes, photodiodes that convert optical signals to current signals, and transimpedance amplifiers (TIAs) that convert the current signals output from photodiodes to voltage signals.

[0007] In active cables, in addition to sending signals (main signals, LFPS signals) from one terminal communication device to another, Electrical Idle information is also transmitted. The LFPS signal (Low Frequency Periodic Signaling) is a low-speed toggle mode signal sent between channel adapters to establish communication. The period of the LFPS signal is 20–100 ns. In the USB 3.2 standard, the LFPS signal has at least 2 cycles, and in the USB 4 standard, it has at least 16 cycles. The shortest LFPS signal transmission period is 40 ns. Electrical Idle (hereinafter referred to as "EI") is not the voltage of logic level L or logic level H of the voltage signal, but rather a voltage level intermediate between the two.

[0008] Patent Document 1 discloses a communication device intended for use in an AOC terminal. In this document, the optical signal transmitted from one terminal-side communication device to another terminal-side communication device has a main signal with its inherent logic level H and logic level L, a fixed value of logic level H for the LFPS signal throughout the LFPS signal transmission period, and a fixed value of logic level L for EI information throughout the EI state. Furthermore, the optical signal transmitted from one terminal-side communication device to another terminal-side communication device includes pulse signals for identifying the timing of changes from EI information transmission to main signal transmission and the timing of changes from EI information transmission to LFPS signal transmission.

[0009] In this document, a communication device receiving an optical signal as described above determines that it is in the EI state period when the received signal remains at logic level L for a continuous period. When the received signal transitions from logic level L to logic level H and remains at logic level H for a fixed period, the communication device determines that it has transitioned from the EI state period to the LFPS signal transmission period. Then, the communication device, detecting the transition to the LFPS signal transmission period, regenerates the LFPS signal using its built-in oscillator and outputs this regenerated LFPS signal to the next stage. The length of the output LFPS signal period is equal to the length of the LFPS signal transmission period. Furthermore, if the received signal contains a predetermined pulse signal after transitioning from logic level L to logic level H, the communication device determines that it has transitioned from the EI state period to the main signal transmission period, amplifies the received main signal, and outputs it to the next stage.

[0010] [Patent Document 1] U.S. Patent No. 10,425,161 Summary of the Invention

[0011] The inventors have discovered that the communication device disclosed in Patent Document 1 has the following problems.

[0012] The communication device disclosed in this document, as a path for outputting electrical signals based on received optical signals, has a first output driver for outputting the main signal and a second output driver for outputting the regenerated LFPS signal. Therefore, the load capacitance at the output end becomes large, making it difficult to output high-speed signals. For example, in USB4 Gen3, the data rate of the main signal (per channel) is 20Gbps, but it is difficult to output such a high-speed signal. Even assuming only one output driver is used, and even if a selector for switching paths is placed before that output driver, the load at the output end of the selector is heavy, making it difficult to achieve high speed.

[0013] This problem is believed to arise from the use of a limiting amplifier type laser driver and TIA. The limiting amplifier can only output two values: logic level H and logic level L, and cannot output the intermediate level between H and L. That is, it cannot transmit a light signal with the intensity corresponding to the intermediate voltage level in the EI state.

[0014] Therefore, in the invention disclosed in Patent Document 1, regarding EI information, the optical signal is set to a fixed value of logic level L throughout the entire EI state. On the other hand, for LFPS signals, the optical signal is set to a fixed value of logic level H throughout the entire LFPS signal transmission period, and only information during the LFPS signal transmission period is transmitted. Therefore, in addition to a first output driver for outputting the main signal, the communication device also needs a built-in oscillator for regenerating the LFPS signal and a second output driver for outputting the regenerated LFPS signal. Thus, since two output drivers need to be configured in parallel, the load capacitance at the output end becomes large, making it difficult to output high-speed signals.

[0015] To address this problem, a linear amplifier type laser driver and TIA are considered instead of a limiting amplifier type. The relationship between the input signal level and the output signal level of a linear amplifier is approximately linear. Therefore, if a linear amplifier type laser driver and TIA are used, regardless of whether it is the main signal, the LFPS signal, or the EI, a waveform of an optical signal that retains the original waveform of the electrical signal can be formed on the transmitting side, and a waveform of an electrical signal that retains the original waveform of the optical signal can be formed on the receiving side. Therefore, the built-in oscillator and the second output driver required in the communication device disclosed in Patent Document 1 are unnecessary; only one output driver is needed. As a result, the aforementioned problems of the communication device disclosed in Patent Document 1 are solved.

[0016] However, when using a linear amplifier-type laser driver and TIA, the following additional problems arise. Even in states where power consumption can be reduced (e.g., Figure 2 The Rx.Detect state (or U3 state) in the state transition diagram of the USB 3.2 standard shown can also result in a situation where power consumption cannot be reduced (or the reduction in power consumption is insufficient). In a state where power consumption can be reduced, it is essentially in the EI state. At this time, the laser driver continues to supply an intermediate current to the diode laser, and the photodiode continues to output an intermediate current. As a result, although it is a state where power consumption should be reduced, it cannot be reduced. Furthermore, Figure 2This is the state transition diagram of the USB 3.2 standard (Link Training and Status State Machine (LTSSM)). This diagram is described in the USB standard (Universal Serial Bus 3.2 Specification, September 22, 2017), so it will be explained simply. If a warm reset is performed from the inactive state (S1) of the SS signal or a far-end receiver termination occurs (R... RX-DC If the received signal Rx is absent, the system transitions to the Rx.Detect state (S2). Additionally, if a power-on reset, warm reset, or removal occurs only on the DS (downstream) port, the system transitions to the Rx.Detect state (S2). If the end of the received signal Rx is detected, the system transitions to the Polling state (S3). After the training process from the Polling state (S3), the state U0 (S4) indicates that the enhanced high-speed link is activated, packet transmission is in progress, or the link is idle. The state U0 (S4) can transition from state U0 to the low-power link state U1 (S5), the even lower-power link state U2 (S6), and the active power-saving link suspend state U3 (S7), respectively, in accordance with the link commands LG0_U1, LG0_U2, and LG0_U3. In state U0 (S4), upon detecting an error, the system transitions to the recovery state (S8), from which it can transition to the hot reset state (S9), lookback state (S10), or the inactive state of the SS signal (S1). It can also transition from the polling state (S3) to the compliance mode state (S11) via the initial LFPS timeout, or to the invalid state of the SS signal (S12) via other timeouts. In the transitions between states, various conditions, such as handshakes, are pre-set in addition to timeouts. Furthermore, in the polling state (S3), if the counter (cPolling Timeout) measures a continuous transition event from the polling state to the Rx.Detect state caused only by timeout in the DS (downstream) port, the system transitions to the inactive state of the SS signal (S1). In the Rx.Detect state (S2), if the received signal Rx exceeds the limit only in the US (upstream) port, the system transitions to the invalid state of the SS signal (S12).

[0017] Even when using a linear amplifier-type laser driver and TIA, power consumption can be reduced by simply shutting down the power each time the EI state is detected. However, there is a risk that the length of the LFPS signal transmission period sandwiched between EI states will be shortened, leading to communication establishment failures. That is, the transition from the EI state to the LFPS signal transmission period not only takes a long time but also has a large time deviation. On the other hand, the transition from the LFPS signal transmission period to the EI state can be performed in a short time. Therefore, if power is shut down every time the EI state is detected, the length of the LFPS signal transmission period will be shortened, potentially leading to communication establishment failures.

[0018] This invention was made to solve the aforementioned problems, and its object is to provide a communication device that, when disposed at either the first or second end of an active optical cable (AOC) for communication between a first end and a second end, enables high-speed communication and reduces power consumption. Furthermore, this invention aims to provide a terminal device equipped with such a communication device and an active optical cable (AOC).

[0019] The communication device is disposed on the first end or the second end of an active optical cable, and the active optical cable uses a laser diode and a photodiode disposed on the first end and the second end respectively to communicate between the first end and the second end.

[0020] The communication device comprises: (1) a differential input terminating resistor that terminates a differential input terminal with a variable resistance value, wherein the differential input terminal receives a signal to be sent to the other communication device as a differential signal; (2) a linear laser driver that provides a current signal to a laser diode based on the signal to be sent to the other communication device, thereby outputting an optical signal from the laser diode; (3) a transmission signal detection unit that detects whether the input signal to the differential input terminal is electrically idle; (4) a linear transimpedance amplifier that receives a current signal output from a photodiode, converts the current signal into a voltage signal, and outputs the voltage signal, wherein the photodiode receives an optical signal arriving from the other communication device; (5) a linear variable gain amplifier that amplifies and outputs the voltage signal output from the linear transimpedance amplifier; and (6) a linear output driver that outputs the voltage signal from the linear variable gain amplifier to the output destination device and is capable of detecting... The output destination device's input terminal resistance is measured; and (7) a pulse count detection unit monitors the current signal output from the photodiode or the voltage signal output from the linear transimpedance amplifier, and detects the pulse count of these current signals or voltage signals; (8) a receive signal detection unit monitors the current signal output from the photodiode or the voltage signal output from the linear transimpedance amplifier, and detects whether these current signals or voltage signals are electrically idle; and (9) a control unit, based on the electrical idle detection result of the transmit signal detection unit, the output destination device's input terminal resistance detection result of the linear output driver, the pulse count detection result of the pulse count detection unit, and the electrical idle detection result of the receive signal detection unit, controls the transition between the active state that can transmit signals and the sleep state that can reduce power consumption, and controls the operation of the differential input terminal resistor, the linear laser driver, the linear transimpedance amplifier, the linear variable gain amplifier, and the linear output driver.

[0021] The control unit (a) determines the transition from the sleep state to the active state when the input signal is not electrically idle as detected by the transmit signal detection unit, or when the pulse count detected by the pulse count detection unit is the pulse count indicating the transition from the sleep state to the active state; (b) determines the transition from the active state to the sleep state based on the condition that the input signal is electrically idle as detected by the transmit signal detection unit, or the condition that the current signal or voltage signal is electrically idle as detected by the receive signal detection unit; (c) controls the supply of the current signal to the laser diode by the linear laser driver according to the detection result of the input termination resistor of the output destination device by the linear output driver, and whether it is the active state or the sleep state; (d) controls the resistance value of the differential input termination resistor according to the pulse count detection result of the pulse count detection unit; and (e) controls the operation of the linear transimpedance amplifier, the linear variable gain amplifier, and the linear output driver according to whether it is the active state or the sleep state.

[0022] Preferably, the communication device further includes an amplitude detection unit that detects the amplitude of the voltage signal output from the linear variable gain amplifier, and a control unit that controls the gain of the linear variable gain amplifier based on the amplitude detection result of the amplitude detection unit.

[0023] In this communication device, preferably, the linear laser driver includes: a low-speed driver that supplies a current signal to the laser diode based on a control signal from the control unit; and a high-speed driver that supplies a current signal to the laser diode based on an input signal to the differential input terminal. The control unit controls the supply of the current signal to the laser diode by the low-speed driver based on the detection result of the linear output driver on the input terminal resistance of the output destination device, and whether it is an active state or a sleep state. The control unit controls the supply of the current signal to the laser diode by the high-speed driver based on whether it is an active state or a sleep state.

[0024] In this communication device, it is preferable that the control unit makes the number of pulses of the current signal supplied from the linear laser driver to the laser diode different when the detection result of the linear output driver to the input terminal resistance of the output destination device is high impedance, when the detection result of the linear output driver to the input terminal resistance of the output destination device is low impedance, and when transitioning from a sleep state to an active state.

[0025] In this communication device, it is preferable that the control unit decides to transition from the active state to the sleep state when the transmitting signal detection unit detects that the current signal or voltage signal is electrically idle for the entire period of the fixed period, or when the receiving signal detection unit detects that the current signal or voltage signal is electrically idle for the entire period of the fixed period.

[0026] The terminal device includes: the aforementioned communication device; a laser diode that receives a current signal supplied from a linear laser driver of the communication device and outputs an optical signal to the other party's communication device; and a photodiode that receives the optical signal arriving from the other party's communication device and outputs a current signal to a linear transimpedance amplifier of the communication device.

[0027] The active optical cable includes: a first terminal device and a second terminal device as the aforementioned terminal devices; a first optical fiber that guides light from the optical signal output from the laser diode of the first terminal device to the photodiode of the second terminal device; and a second optical fiber that guides light from the optical signal output from the laser diode of the second terminal device to the photodiode of the first terminal device.

[0028] A communication device mounted on an active optical fiber includes: a variable resistor connected between the differential input terminals of a linear laser driver; a transmit signal detection unit connected to the differential input terminals; a linear transimpedance amplifier connected to a photodiode; a linear variable gain amplifier connected to the output terminal of the linear transimpedance amplifier; a linear output driver connected to the output terminal of the linear variable gain amplifier; a pulse count detection unit connected to the photodiode; a receive signal detection unit connected to the output terminal of the linear transimpedance amplifier; and a control unit having multiple input terminals and multiple output terminals. The input terminals of the control unit are connected to the output terminals of the pulse count detection unit and the receive signal detection unit, and the output terminals of the control unit are connected to the resistance value control terminal of the variable resistor, the control signal input terminal of the linear laser driver, the control signal input terminal of the linear transimpedance amplifier, and the control signal input terminal of the linear variable gain amplifier.

[0029] In active optical cables (AOCs) that enable communication between the first and second ends, high-speed communication and reduced power consumption can be achieved. Attached Figure Description

[0030] Figure 1 This diagram shows the structure of two devices connected via a communication cable conforming to the USB4 standard.

[0031] Figure 2 This is the state transition diagram of the USB 3.2 standard.

[0032] Figure 3 This is a diagram showing the structure of Active Optical Cable (AOC) 1.

[0033] Figure 4 This is a diagram showing the structure of communication device 111 and communication device 121.

[0034] Figure 5 This is a state transition diagram showing the transition between the active state and the sleep state.

[0035] Figure 6 yes Figure 2 The state transition diagram shown is a polling state transition diagram of the USB 3.2 standard.

[0036] Figure 7 This is an explanation Figure 6 The diagram shows the signal transmission and reception between two link partners in polling mode.

[0037] Figure 8 This is a diagram showing an example of a linear laser driver 12.

[0038] Label Explanation

[0039] 1…Active Optical Cable (AOC), 10…Control Unit, 11…Differential Input Termination Resistor, 12…Linear Laser Driver, 13…Transmit Signal Detection Unit, 14…Linear Transimpedance Amplifier (Linear TIA), 15…Linear Variable Gain Amplifier (Linear VGA), 16…Linear Output Driver, 17…Pulse Count Detection Unit, 18…Received Signal Detection Unit, 19…Amplitude Detection Unit, 20…Control Unit, 21…Differential Input Termination Resistor, 22…Linear Laser Driver, 23…Transmit Signal Detection Unit, 24…Linear Transimpedance Amplifier (Linear TIA), 25… Linear variable gain amplifier (linear VGA), 26… linear output driver, 27… pulse count detection unit, 28… received signal detection unit, 29… amplitude detection unit, 110… terminal device, 111… communication device, 112… laser diode, 113… photodiode, 114… connector, 120… terminal device, 121… communication device, 122… laser diode, 123… photodiode, 124… connector, 131, 132… optical fiber, 140… link partner, 141… channel adapter, 150… link partner, 151… channel adapter. Detailed Implementation

[0040] Hereinafter, with reference to the accompanying drawings, the methods for carrying out the invention will be described in detail. Furthermore, in the description of the drawings, the same elements are labeled with the same reference numerals, and repeated descriptions are omitted. The invention is not limited to these illustrations, but is shown in the claims, and is intended to include all modifications with the same meaning and scope as the claims.

[0041] Figure 3This diagram illustrates the structure of Active Optical Cable (AOC) 1. AOC 1 communicates between channel adapter 141 of one link partner 140 and channel adapter 151 of another link partner 150. Channel adapters 141 and 151 can conform to either the USB 3.2 or USB 4 standard. AOC 1 uses a laser diode and a photodiode, respectively located on the first and second ends, to communicate between the first and second ends.

[0042] Terminal device 110 located at the first end of AOC1 includes a communication device 111, a laser diode 112, a photodiode 113, and a connector 114. Connector 114 is connected to channel adapter 141. Terminal device 120 located at the second end of AOC1 includes a communication device 121, a laser diode 122, a photodiode 123, and a connector 124. Connector 124 is connected to channel adapter 151. An optical fiber 131 for transmitting optical signals is disposed between laser diode 112 and photodiode 123. An optical fiber 132 for transmitting optical signals is disposed between laser diode 122 and photodiode 113.

[0043] Figure 4 This diagram illustrates the structures of communication devices 111 and 121. Communication device 111 includes a control unit 10, a differential input terminating resistor 11, a linear laser driver 12, a transmit signal detection unit 13, a linear transimpedance amplifier (linear TIA) 14, a linear variable gain amplifier (linear VGA) 15, a linear output driver 16, a pulse count detection unit 17, a receive signal detection unit 18, and an amplitude detection unit 19. Communication device 121 includes a control unit 20, a differential input terminating resistor 21, a linear laser driver 22, a transmit signal detection unit 23, a linear transimpedance amplifier (linear TIA) 24, a linear variable gain amplifier (linear VGA) 25, a linear output driver 26, a pulse count detection unit 27, a receive signal detection unit 28, and an amplitude detection unit 29. Communication devices 111 and 121 have identical structures, and structural elements with the same name have the same function. Hereinafter, communication device 111 will be primarily described.

[0044] The differential input terminating resistor 11 is the terminal of the differential input, which receives the signal to be transmitted to the communication device 121 as a differential signal from the channel adapter 141. The resistance value of the differential input terminating resistor 11 is variable and is set according to the control signal provided from the control unit 10.

[0045] The linear laser driver 12 provides a current signal to the laser diode 112 based on a signal to be transmitted to the communication device 121, and causes the laser diode 112 to output an optical signal. The linear laser driver 12 is a linear amplifier type laser driver, where the relationship between the input voltage signal level and the output current signal level is approximately linear. The operation of the linear laser driver 12 is controlled by a control signal provided from the control unit 10. In addition to providing a current signal to the laser diode 112 based on a signal input from the channel adapter 141, the linear laser driver 12 sometimes also provides a current signal to the laser diode 112 based on a control signal provided from the control unit 10.

[0046] The transmit signal detection unit 13 monitors the input signal to the differential input terminal, detects whether the input signal is EI, and sends a TxSD signal indicating the detection result to the control unit 10. The transmit signal detection unit 13 can also monitor the signals inside the linear laser driver 12.

[0047] The linear TIA14 receives the current signal output from photodiode 113, which receives the optical signal arriving from the communication device 121. The linear TIA14 converts this current signal into a voltage signal and outputs it to the linear VGA15. The linear TIA14 is a linear amplifier type, and the relationship between the input current signal level and the output voltage signal level is approximately linear. The operation of the linear TIA14 is controlled by a control signal provided by the control unit 10.

[0048] The linear VGA15 amplifies the voltage signal output from the linear TIA14 and outputs the amplified voltage signal to the linear output driver 16. The gain of the linear VGA15 is variable and is set by a control signal provided from the control unit 10. The linear VGA15 is a linear amplifier type, and the relationship between the input voltage signal level and the output voltage signal level is approximately linear. The operation of the linear VGA15 is controlled by the control signal provided from the control unit 10.

[0049] The linear output driver 16 outputs the voltage signal from the linear VGA 15 to the output destination device (channel adapter 141). The linear output driver 16 can also amplify the input voltage signal with a fixed gain and output the amplified voltage signal. The linear output driver 16 is a linear amplifier type; if the gain is constant, the relationship between the input voltage signal level and the output voltage signal level is approximately linear. The operation of the linear output driver 16 is controlled by a control signal provided from the control unit 10.

[0050] Furthermore, the linear output driver 16 can detect the input termination resistance of the output destination device (channel adapter 141) and send an RxDet signal indicating the detection result to the control unit 10. For example, the input termination resistance of the output destination device can be detected by detecting the response speed of the potential change when a pulse signal is output to the output destination device. The response is fast when the input terminal of the output destination device is disconnected. The response is slow when the input terminal of the output destination device is connected. The detection of the input termination resistance of the output destination device by the linear output driver 16 can be performed even when the linear output driver 16 is powered off.

[0051] The pulse count detection unit 17 monitors the current signal output from the photodiode 113 or the voltage signal output from the linear TIA 14, detects the pulse count of these current or voltage signals, and sends a PN signal representing the detection result to the control unit 10. The pulse count detection unit 17 can monitor any of the following: the current signal output from the photodiode 113, the voltage signal output from the linear TIA 14, the voltage signal output from the linear VGA 15, and the voltage signal output from the linear output driver 16. As shown, the pulse count detection unit 17 preferably monitors the current signal output from the photodiode 113. By monitoring the current signal output from the photodiode 113 by the pulse count detection unit 17, all circuits after the linear TIA 14 can be powered down.

[0052] The receive signal detection unit 18 monitors the current signal output from the photodiode 113 or the voltage signal output from the linear TIA 14, detects whether these current or voltage signals are EI (Excessive I), and sends an RxSD signal indicating the detection result to the control unit 10. The receive signal detection unit 18 can monitor any one of the following: the current signal output from the photodiode 113, the voltage signal output from the linear TIA 14, the voltage signal output from the linear VGA 15, and the voltage signal output from the linear output driver 16. As shown, the receive signal detection unit 18 is preferably located before the linear VGA 15. By monitoring the voltage or current signal at the front end of the linear VGA 15, the receive signal detection unit 18 can detect whether it is EI regardless of the gain of the linear VGA 15.

[0053] The amplitude detection unit 19 detects the amplitude of the voltage signal output from the linear VGA 15 and sends a PK signal representing the detection result to the control unit 10. The amplitude detection unit 19 can also monitor the voltage signal output from the linear output driver 16, but this is not preferable due to the increased output load capacity and worsened return loss. As shown, the amplitude detection unit 19 preferably monitors the voltage signal output from the linear VGA 15. Furthermore, the amplitude detection unit 19 preferably detects the average amplitude of the voltage signal over the entire period of a fixed time.

[0054] The control unit 10 receives the following signals: a TxSD signal representing the EI detection result output from the transmit signal detection unit 13; an RxDet signal representing the output destination device input termination resistance detection result output from the linear output driver 16; a PN signal representing the pulse count detection result output from the pulse count detection unit 17; an RxSD signal representing the EI detection result output from the receive signal detection unit 18; and a PK signal representing the amplitude detection result output from the amplitude detection unit 19. Based on these input TxSD, RxDet, PN, RxSD, and PK signals, the control unit 10 controls the transition between an active state capable of transmitting signals and a sleep state capable of reducing power consumption.

[0055] In addition, based on these input signals, the control unit 10 outputs a Term signal for setting the resistance value of the differential input terminal resistor 11, a TxEN signal and an LS signal for controlling the operation of the linear laser driver 12, an RxEN signal for controlling the operation of the linear TIA 14, the linear VGA 15 and the linear output driver 16, and a GCTL signal for controlling the gain of the linear VGA 15.

[0056] Figure 5 This is a state transition diagram representing the transition between the active state (S53) and the sleep state. The active state (S53) is the state in which signals can be sent. The sleep state is the state in which power consumption is reduced. The sleep state includes the unplug state (S51) and the plug state (S52).

[0057] Based on the output destination device input termination resistance detection result represented by the RxDet signal output from the linear output driver 16, a transition between the unplug state (S51) and the plug state (S52) is performed. That is, if the output destination device is connected, the transition is to the plug state (S52), and if the output destination device is not connected, the transition is to the unplug state (S51). In addition, based on the EI detection result represented by the TxSD signal output from the transmit signal detection unit 13, the pulse count detection result represented by the PN signal output from the pulse count detection unit 17, and the EI detection result represented by the RxSD signal output from the receive signal detection unit 18, a transition between the plug state (S52) and the active state (S53) is performed.

[0058] Figure 5 The states in the state transition diagram shown are... Figure 2 The correspondences between the states in the state transition diagram of the USB 3.2 standard are shown below. The unplugged state includes... Figure 2 The state transition diagram of the USB 3.2 standard shows the states of SS.Disabled and Rx.Detect (terminal closed). The insertion state (S52) includes... Figure 2 The state transition diagram of the USB 3.2 standard shows the states of Rx Detect (terminal connected), U2, U3, and SS.Inactive. The active state (S53) includes... Figure 2 The state transition diagram of the USB 3.2 standard shows the states of Polling, U0, U1, and Recovery.

[0059] The control unit 10 determines the transition from the sleep state to the active state based on the TxSD signal or the PN signal. That is, the control unit 10 determines the transition from the sleep state to the active state (S53) when the input signal is not detected by the transmission signal detection unit 13 or when the number of pulses detected by the pulse count detection unit 17 indicates a transition from the sleep state to the active state (S53).

[0060] The control unit 10 determines the transition from the active state (S53) to the sleep state based on the TxSD signal or the RxSD signal. That is, the control unit 10 determines the transition from the active state (S53) to the sleep state based on the case where the input signal is detected as EI by the transmitting signal detection unit 13 or the current signal or voltage signal is detected as EI by the receiving signal detection unit 18.

[0061] Preferably, the control unit 10 determines the transition from the active state (S53) to the sleep state when the input signal is EI detected by the transmitting signal detection unit 13 during the entire fixed period, or when the current signal or voltage signal is EI detected by the receiving signal detection unit 18 during the entire fixed period. The length of the fixed period is preferably 240 ms or more.

[0062] The control unit 10 controls the supply of current signals from the linear laser driver 12 to the laser diode 112 based on the RxDet signal and the state (whether it is an active state or a sleep state). That is, the control unit 10 controls the supply of current signals from the linear laser driver 12 to the laser diode 112 based on the detection result of the linear output driver 16 on the input termination resistance of the output destination device, and whether it is an active state or a sleep state.

[0063] Specifically, the control unit 10, based on the LS signal provided to the linear output driver 16, determines the number of pulses of the current signal supplied from the linear laser driver 12 to the laser diode 112 differently depending on whether the linear output driver 16 detects a high impedance at the input termination resistance of the output destination device, a low impedance at the input termination resistance of the linear output driver 16 to the output destination device, or when transitioning from a sleep state to an active state. Furthermore, the control unit 10 uses the TxEN signal provided to the linear output driver 16 to switch the active / inactive input of the electrical signal from the differential input terminal, and disables the input of the electrical signal from the differential input terminal during the output pulse signal period using the LS signal. Additionally, in the sleep state, the control unit 10 stops the supply of the current signal from the linear laser driver 12 to the laser diode 112.

[0064] The pulse count indicated by the LS signal is the number of pulses that repeat within a fixed period with a fixed pulse width and a fixed interval, starting from the moment when logic level L transitions to logic level H after a certain period. The pulse count can also be 1, in which case it means that only one pulse of a fixed pulse width exists within the fixed period, starting from the moment when logic level L transitions to logic level H after a certain period. Alternatively, the pulse count can be 0, in which case it means that logic level L continues for the entire period exceeding a predetermined time. The pulse count detection unit 17 detects the pulse count based on these parameters.

[0065] The control unit 10 controls the resistance value of the differential input termination resistor 11 based on the PN signal and by providing the Term signal to the differential input termination resistor 11. That is, the control unit 10 obtains information about the input termination resistance of the output destination device (channel adapter 151) detected by the linear output driver 26 of the other party's communication device 121 based on the pulse count detection result of the pulse count detection unit 17, and controls the resistance value of the differential input termination resistor 11 based on this information.

[0066] Specifically, the control unit 10 sets the differential input termination resistor 11 to high impedance when the input termination resistance of the output destination device (channel adapter 151) in the other party's communication device 121 is high impedance, and sets the differential input termination resistor 11 to low impedance when the input termination resistance of the output destination device (channel adapter 151) in the other party's communication device 121 is low impedance. The channel adapter 141 can detect the connection / disconnection of the input termination resistance of the other party's channel adapter 151 by detecting the resistance value of the differential input termination resistor 11.

[0067] In this way, the result of the linear output driver 26 of the other party's communication device 121 detecting the input terminal resistance of the destination device is sent as an optical signal pulse from the laser diode 122 driven by the linear laser driver 22 of the other party's communication device 121, and this optical signal is received by the photodiode 113. Then, based on the pulse count detection result of the pulse count detection unit 17 which inputs the current signal output from the photodiode 113, the impedance of the differential input terminal resistor 11 is set according to the impedance of the input terminal resistance of the destination device (channel adapter 151) in the other party's communication device 121. This function is called the RxDetect function. In addition, communication using the optical signal of the result of the output terminal resistance detection of the destination device of the linear output driver 26 of the other party's communication device 121 is called RxDetect communication.

[0068] The control unit 10 outputs an RxEN signal based on whether the system is in an active or sleep state, thereby controlling the operation of the linear TIA 14, linear VGA 15, and linear output driver 16. Specifically, in the sleep state, the control unit 10 reduces or stops the power supplied to the linear TIA 14, linear VGA 15, and linear output driver 16, thereby reducing power consumption.

[0069] The control unit 10 controls the gain of the linear VGA 15 based on the PK signal and by providing the GCTL signal to the linear VGA 15. Specifically, the control unit 10 controls the gain of the linear VGA 15 based on the amplitude detection result of the amplitude detection unit 19, so that the amplitude of the voltage signal output from the linear VGA 15 is at or within the target value.

[0070] In addition, such as Figure 8 As shown, the linear laser driver 12 can also be configured to include a low-speed driver 12A that supplies a current signal to the laser diode 112 based on an LS signal from the control unit 10, and a high-speed driver 12B that supplies a current signal to the laser diode 112 based on a differential signal DIFF input to the differential input terminal. These low-speed drivers 12A and high-speed drivers 12B are connected in parallel. An LS signal is input to the low-speed driver 12A, and a differential signal DIFF supplied to both ends of the differential input terminating resistor 11 is input to the high-speed driver 12B. In this case, the control unit 10 controls the supply of the current signal from the low-speed driver 12A to the laser diode 112 based on the detection result of the output destination device input terminating resistor of the linear output driver 16, and whether it is in an active or sleep state. Furthermore, the control unit 10 controls the supply of the current signal from the high-speed driver 12B to the laser diode 112 based on whether it is in an active or sleep state. The high-speed driver 12B can also be a linear amplifier type, and the low-speed driver 12A can also be a limiting amplifier type. Furthermore, the description of the low-speed driver 12A and high-speed driver 12B in one party's communication device 111 can be replaced with the description of the low-speed driver and high-speed driver in the other party's communication device 121.

[0071] In this embodiment, during RxDetect communication, an optical signal containing predetermined pulse information is transmitted. RxDetect communication is performed while in sleep mode. Through RxDetect communication, when the input terminal of the output destination device (channel adapter 151) in the other party's communication device 121 is connected, the communication device transitions from a disconnected state to an inserted state. When the input terminal of the output destination device (channel adapter 151) in the other party's communication device 121 is disconnected, the communication device transitions from an inserted state to a disconnected state.

[0072] In the sleep state, which includes both the unplugged state (S51) and the plugged state (S52), the TxEN signal provided from the control unit 10 to the linear laser driver 12 invalidates the signal input to the differential input terminal. Furthermore, the LS signal provided from the control unit 10 to the linear laser driver 12 makes the current supplied from the linear laser driver 12 to the laser diode 112 approximately 0mA. RxDetect communication is implemented based on the LS signal, corresponding to the output destination device input terminal resistance detection result (Rx Detect result) of the linear output driver 16, which is performed at a fixed period.

[0073] In sleep mode, the linear TIA 14, linear VGA 15, and linear output driver 16 can be powered down via the RxEN signal output from the control unit 10. At this time, the linear output driver 16 can generate and output an EI potential. Even in the power-down state, the linear output driver 16 can still generate an EI potential and perform RxDetect. The pulse count detection unit 17 detects the number of pulses transmitted via RxDetect communication, and the control unit 10 can set the resistance value of the differential input termination resistor 11 based on the pulse count detection result.

[0074] Switching between normal communication (communication using the main signal or LFPS signal) and RxDetect communication is performed using an optical signal that includes pulse information. In the sleep state, the system transitions from the sleep state to the active state when the transmitting signal detection unit 13 detects a signal input, or when the pulse count detection result of the pulse count detection unit 17 indicates a transition to the active state.

[0075] When transitioning from sleep mode to active mode, the signal input to the linear laser driver 12 is activated by the TxEN signal provided to the linear laser driver 12 from the control unit 10. The linear TIA 14, linear VGA 15, and linear output driver 16 are started by the RxEN signal output from the control unit 10. Furthermore, the gain of the linear VGA 15 is controlled by the GCTL signal provided to the linear VGA 15 from the control unit 10. Additionally, the linear output driver 16 can be started either before or after the gain control of the linear VGA 15 is completed.

[0076] Until it returns to a state that can reduce power consumption (e.g.) Figure 2 Before the RxDetect state (or U3 state) shown in the state transition diagram of the USB 3.2 standard, EI information can be transmitted using an intermediate level via linear communication. If the receive signal detection unit 18 detects EI, the control unit 10 stops controlling the gain of the linear VGA 15. After the EI detection performed by the receive signal detection unit 18 or the transmit signal detection unit 13, if no signal arrives within a short period, the system transitions from the active state to the sleep state. During signal detection performed by the receive signal detection unit 18 or the transmit signal detection unit 13, the system remains in the active state.

[0077] According to this embodiment, the following effects can be obtained. The AOC1 equipped with communication devices 111, 121, etc., can implement the RxDetect function and can handle either the USB 3.2 standard or the USB 4 standard. However, the present invention is not limited to handling the USB 3.2 standard and the USB 4 standard.

[0078] In the communication device disclosed in Patent Document 1, two output drivers need to be connected in parallel. In contrast, in this embodiment, only one linear output driver 16 is required as the output driver. Therefore, in this embodiment, the increase in the load capacity of the output terminal is suppressed, high-speed signals can be easily output, and the data rate (per channel) of the main signal in USB4 Gen3 is 20Gbps.

[0079] In this embodiment, during sleep mode, the linear laser driver 12 is essentially inactive for the input signal, with an output current of 0mA, outputting a current signal only during RxDetect communication. Furthermore, during sleep mode, the linear TIA 14, linear VGA 15, and linear output driver 16 are powered down, maintaining a state of minimal power consumption. Therefore, in this embodiment, in... Figure 2 The RxDetect and U3 states shown in the USB 3.2 standard state transition diagram reduce power consumption. Even when sending RxDetect information via pulse signals, the signal path does not need to be activated every time, thus maintaining low power consumption.

[0080] like Figure 2 As shown in the state transition diagram of the USB 3.2 standard, after power-on, it first enters the Rx.Detect state. Upon detecting a connected device in the Rx.Detect state, it transitions to the Polling state. After a successful transaction in the Polling state, it transitions to the U0 state, which is the active state. Even if a portion of the initial LFPS signal transmission period after the polling state transition is lost, no problem will occur. This will be explained below.

[0081] Figure 6 yes Figure 2 The diagram shown is a state transition diagram of the polling state in the USB 3.2 standard. This diagram is described in the USB standard (Universal Serial Bus 3.2 Specification, September 22, 2017), and therefore will be explained simply. Additionally, Figure 7 This is an explanation Figure 6 The diagram shown illustrates the signal transmission and reception between two link partners in polling mode. The left side shows the communication sequence of one link partner (communication device 111 side), and the right side shows the communication sequence of the other link partner (communication device 121 side).

[0082] like Figure 7As shown, firstly, to establish communication, the SCD1.LFPS signal is sent from the first link partner to the second link partner (S71) (handshake). SCD is an abbreviation for "SS Capability Declaration," SCD1 is a signal representing "0010," and the SCD1.LFPS signal represents the SCD1 signal in LFPS. Next, the second link partner, having received this signal, sends the SCD1.LFPS signal to the first link partner (S81) (handshake). Then, the first link partner, having received this signal, sends the SCD2.LFPS signal to the second link partner (S72) (handshake). Additionally, SCD2 is a signal representing "1101," and the SCD2.LFPS signal represents the SCD2 signal in LFPS. Finally, the second link partner, having received this signal, sends the SCD2.LFPS signal to the first link partner (S82) (handshake). Next, the first link partner that received the signal sends an LBPM signal to the second link partner (S73) (handshake). LBPM is an abbreviation for "LFPS Based PWM Signaling". Then, the second link partner that received the signal sends the LBPM signal back to the first link partner (S83) (handshake). Next, to perform the training sequence, the first link partner that received the signal sends a TSEQ signal to the second link partner (S74). TSEQ is an abbreviation for "Training Sequence Equalizer". Next, to perform the training sequence, the second link partner that received the signal sends the TSEQ signal back to the first link partner (S84). Next, the first link partner that received this information sends the first training sequence (TS1) to the second link partner (S75). Next, the second link partner that received this information sends the first training sequence (TS1) back to the first link partner (S85). Next, the first link partner that received the information sends the second training sequence (TS2) to the second link partner (S76). Then, the second link partner that received the information sends the second training sequence (TS2) to the first link partner (S86). This exits the polling state. Figure 2 S3), the first link partner becomes state U0 ( Figure 2 Similarly, in S4)(S77), the second link partner also becomes state U0 ( Figure 2 S4)(S87).

[0083] Figure 6 Detailed description Figure 7The sequence is as follows. When the state transitions from Rx.Detect to Polling, it first becomes Polling.LFPS (S61) and performs a handshake using the SCD1.LFPS signal described above. Then, it becomes Polling.LFPSPlus (S62) and performs a handshake using the SCD2.LFPS signal described above.

[0084] Next, the aforementioned LBPM handshake is performed. In the Polling.PortMatch state (S63), the two ports perform the LBPM handshake. In the Polling.PortConfig state (S64), the port sets its own state based on the PHY capability LBPM referenced in Polling.PortMatch, and synchronizes with its link partner when it enters the Polling.RxEQ state (S65). In the Polling.RxEQ state (S65), signals (TSEQ command sets) for the TSEQ used in the aforementioned training sequence are sent. When it enters the Polling.Active state (S66), the handshake for the first training sequence (TS1) is performed. When it enters the Polling.Configuration state (S67), the handshake for the second training sequence (TS2) is performed, and it enters the Polling.Idle state (S68), transitioning to state U0 (S617). Furthermore, if three state transitions starting from the Polling.LFPS state (S61) fail, it transitions to the eSS.Inavtive state (S611), which is a link error state. When an LFPS timeout occurs, the system transitions from the Polling.LFPS state (S61) to the Compliane Mode state (S612). In the Polling.Configuration state (S67), when a timeout occurs between ports or devices, the system can transition to the Rx.Detect state (S613) or the eSS.Disabled state (S614) where the Enhanced SuperSpeed ​​connection is invalid. Depending on the conditions, the system can transition from the Polling.Idle state (S68) to the Hot reset state (S615) or the loopback state (S616).

[0085] From the Rx.Detect state ( Figure 2 S2) transitions to Polling state ( Figure 3 During the 360ms period following S3, in the Polling.LFPS state (S61) and Polling.LFPSPlus state (S62), the transition to the U0 state is performed normally. Figure 2The condition for S4) is: the two link partners successfully transmit and receive SCD1.LFPS signals and SCD2.LFPS signals, and become the state that exits from the Polling state (S617).

[0086] On the other hand, each component within the communication device 111 of this embodiment can transition from a sleep state to an active state within 30 μs. Therefore, in this embodiment, even if a portion of the initial period of LFPS signal transmission after the polling state transition is lost, the transition to the active state can proceed normally. Note that, assuming a power outage each time the device enters the EI state, a significant portion of the LFPS signal transmission period after the polling state transition is lost, resulting in unsuccessful transmission and reception of the SCD1.LFPS and SCD2.LFPS signals.

[0087] LFPS messages can include Polling.LFPS and Ping.LFPS. Additionally, when the link partner and communication device are in U1 state (S5), they can periodically send Ping.LFPS.

[0088] exist Figure 2 When the Ping.LFPS signal is sent in state U1 (S5) of the state transition diagram of the USB 3.2 standard shown, the communication device 111 of this embodiment performs linear operation in the active state. However, since the LFPS signal transmission period is saved, this is not a problem. This will be explained below. The longest period of the EI state between the Ping.LFPS signal transmission period and the next Ping.LFPS signal transmission period is 240ms. Therefore, in this embodiment, a no-signal state lasting more than 240ms can be used as a condition for transitioning from the active state to the sleep state. As a result, the U1 state (S5) period can remain in the active state, and the Ping.LFPS signal can be sent normally, and the Ping.LFPS signal transmission period is saved. Furthermore, assuming that power is lost every time the device enters the EI state, the shortest Ping.LFPS signal transmission period is 40ns, so sometimes there is not enough time to transition from the sleep state to the active state.

[0089] In this embodiment, a linear VGA 15 is configured to be provided after the linear TIA 14. The rationale for this is explained below. If a linear VGA is not provided after the TIA, the amplitude of the output current signal of the TIA will deviate significantly due to manufacturing deviations of the laser diode and photodiode, as well as optical coupling deviations during installation, sometimes failing to meet the electrical signal amplitude requirements of the USB standard. Therefore, if a linear VGA is not provided after the TIA, to meet the electrical signal amplitude requirements of the USB standard, a limiting amplifier type TIA is required, where the amplitude of the output electrical signal is not affected by the amplitude of the input optical signal. However, using a limiting amplifier type TIA presents the problems described above. Therefore, in this embodiment, a linear VGA is provided after the linear TIA, and the gain of the linear VGA is controlled to ensure that the amplitude of the output electrical signal of the linear VGA meets the electrical signal amplitude requirements of the USB standard.

[0090] In this embodiment, by employing a linear TIA, offset cancellation can be performed during the EI period. This will be explained below. Limiting amplifier type devices only output logic levels H and L, and cannot output the intermediate level during the EI state. Therefore, a fixed value for logic level H or logic level L is not required during the EI state. To perform offset cancellation during TIA, common level information is needed, but with a limiting amplifier type device, a common level signal cannot be transmitted, thus offset cancellation cannot be performed. When offset cancellation cannot be performed during the EI state, it needs to be re-performed each time the LFPS signal is transmitted. If offset cancellation is not performed properly, the duty cycle of the LFPS signal becomes inappropriate, and it cannot become a normal LFPS signal waveform, leading to communication establishment failure. In contrast, in this embodiment, by employing a linear amplifier type device, offset cancellation can be performed not only during LFPS signal transmission but also during the EI state, thus ensuring a normal LFPS signal waveform at all times.

[0091] The communication device disposed in the aforementioned active optical cable includes: a variable resistor 11 connected between the differential input terminals of a linear laser driver 12; a transmit signal detection unit 13 connected to the differential input terminals; a linear transimpedance amplifier 14 connected to a photodiode 113; a linear variable gain amplifier 15 connected to the output terminal of the linear transimpedance amplifier 14; a linear output driver 16 connected to the output terminal of the linear variable gain amplifier 15; a pulse count detection unit 17 connected to the photodiode 113; a receive signal detection unit 18 connected to the output terminal of the linear transimpedance amplifier 14; and a control unit having multiple input terminals and multiple output terminals, wherein the input terminals of the control unit are connected to the output terminals of the pulse count detection unit 17 and the receive signal detection unit 18, and the output terminals of the control unit are connected to the resistance value control terminal of the variable resistor 11, the control signal input terminal of the linear laser driver 12, the control signal input terminal of the linear transimpedance amplifier 14, and the control signal input terminal of the linear variable gain amplifier 15.

[0092] The aforementioned communication device also includes an amplitude detection unit 19 connected to the output terminal of the linear variable gain amplifier 15.

[0093] In the aforementioned communication device, the linear laser driver 12 may include a low-speed driver 12A and a high-speed driver 12B connected in parallel with the laser diode.

[0094] The aforementioned terminal device includes a communication device, a laser diode 112 (or 122) connected to the transmitting terminal of the communication device, and a photodiode 113 (or 123) connected to the receiving terminal of the communication device.

[0095] AOC has a first optical fiber 131 optically coupled to the laser diode of the terminal device and a second optical fiber 132 optically coupled to the photodiode 113.

[0096] As described above, the communication device 111 includes a control unit 10, a differential input terminating resistor 11, a linear laser driver 12, a transmit signal detection unit 13, a linear transimpedance amplifier (linear TIA) 14, a linear variable gain amplifier (linear VGA) 15, a linear output driver 16, a pulse count detection unit 17, a receive signal detection unit 18, and an amplitude detection unit 19. The control unit 10 outputs a Term signal for setting the resistance value of the differential input terminating resistor 11, a TxEN signal and an LS signal for controlling the operation of the linear laser driver 12, an RxEN signal for controlling the operation of the linear TIA 14, the linear VGA 15, and the linear output driver 16, and a GCTL signal for controlling the gain of the linear VGA 15. The structure of the communication device 121 is the same as that of the communication device 111.

[0097] The implementation methods described so far are based on the USB standard, but the present invention is not limited to the USB standard.

Claims

1. A communication device disposed at a first end or a second end in an active optical cable, the active optical cable using a laser diode and a photodiode respectively disposed at the first end and the second end to perform communication between the first end and the second end, the communication device comprising: A differential input terminating resistor, which terminates a differential input terminal and has a variable resistance value, wherein the differential input terminal receives a signal to be sent to the other party's communication device as a differential signal. A linear laser driver that provides a current signal to a laser diode based on a signal to be sent to the other party's communication device, so that an optical signal is output from the laser diode; The signal detection unit detects whether the input signal to the differential input terminal is electrically idle; A linear transimpedance amplifier takes a current signal output from a photodiode as input, converts the current signal into a voltage signal, and outputs the voltage signal, wherein the photodiode receives an optical signal arriving from the other party's communication device. A linear variable gain amplifier that amplifies and outputs a voltage signal from the linear transimpedance amplifier; A linear output driver that outputs a voltage signal from the linear variable gain amplifier to an output destination device and is capable of detecting the input termination resistance of the output destination device; The pulse count detection unit monitors the current signal output from the photodiode or the voltage signal output from the linear transimpedance amplifier, and detects the pulse count of these current signals or voltage signals. The receiving signal detection unit monitors the current signal output from the photodiode or the voltage signal output from the linear transimpedance amplifier, and detects whether these current signals or voltage signals are electrically idle. as well as The control unit, based on the electrical idle detection results of the transmitting signal detection unit, the output destination device input termination resistor detection results of the linear output driver, the pulse count detection results of the pulse count detection unit, and the electrical idle detection results of the receiving signal detection unit, controls the transition between an active state capable of transmitting signals and a sleep state capable of reducing power consumption, and controls the operation of the differential input termination resistor, the linear laser driver, the linear transimpedance amplifier, the linear variable gain amplifier, and the linear output driver, respectively. When the input signal is not electrically idle as detected by the signal transmission detection unit, or when the pulse count detected by the pulse count detection unit is a pulse count indicating a transition from a sleep state to an active state, the control unit decides to transition from the sleep state to the active state. The control unit determines the transition from the active state to the sleep state based on whether the input signal is electrically idle as detected by the transmitting signal detection unit or whether the current or voltage signal is electrically idle as detected by the receiving signal detection unit. The control unit controls the current signal supply of the linear laser driver to the laser diode based on the detection result of the input termination resistance of the output destination device by the linear output driver, and whether it is in an active or sleep state. The control unit controls the resistance value of the differential input terminal resistor based on the pulse count detection result of the pulse count detection unit. The control unit controls the operation of the linear transimpedance amplifier, the linear variable gain amplifier, and the linear output driver according to whether the state is active or dormant.

2. The communication device according to claim 1, wherein, The communication device further includes an amplitude detection unit that detects the amplitude of the voltage signal output from the linear variable gain amplifier. The control unit controls the gain of the linear variable gain amplifier based on the amplitude detection results of the amplitude detection unit.

3. The communication device according to claim 1, wherein, The linear laser driver includes: a low-speed driver that supplies a current signal to the laser diode based on a control signal from the control unit; and a high-speed driver that supplies a current signal to the laser diode based on an input signal to the differential input terminal. The control unit controls the supply of current signal to the laser diode by the low-speed driver based on the detection result of the input termination resistance of the output destination device by the linear output driver, and whether it is in an active or sleep state. The control unit controls the supply of current signal to the laser diode by the high-speed driver based on whether the state is active or dormant.

4. The communication device according to claim 1, wherein, The control unit makes the number of pulses of the current signal supplied from the linear laser driver to the laser diode different when the linear output driver detects a high impedance to the input terminal resistance of the output destination device, when the linear output driver detects a low impedance to the input terminal resistance of the output destination device, and when transitioning from a sleep state to an active state.

5. The communication device according to claim 1, wherein, The control unit determines to transition from the active state to the sleep state when the transmitting signal detection unit detects that the current signal or voltage signal is electrically idle for the entire fixed period, or when the receiving signal detection unit detects that the current signal or voltage signal is electrically idle for the entire fixed period.

6. The communication device according to claim 5, wherein, The length of the fixed period is 240ms or more.

7. A terminal device comprising: The communication device according to claim 1; A laser diode, which receives a current signal from a linear laser driver of the communication device and outputs an optical signal to the other communication device; and A photodiode receives optical signals arriving from the other party's communication device and outputs current signals to the linear transimpedance amplifier of the communication device.

8. An active optical cable, comprising: The first terminal device and the second terminal device are the terminal devices as described in claim 7; The first optical fiber guides the optical signal output from the laser diode of the first terminal device to the photodiode of the second terminal device; and The second optical fiber guides the optical signal output from the laser diode of the second terminal device to the photodiode of the first terminal device.

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