An APC regulating circuit and method

Abstract

The application relates to the technical field of integrated circuit design, in particular to an APC adjusting circuit and method; a logarithmic converter is used to replace a transimpedance amplifier TIA, extraction of a monitoring diode MPD current I PD is realized, and logarithmic conversion of I PD is realized; target MPD current existing in linear relation is converted from target optical power AOP dBm , intuitive and convenient debugging is realized, and the problem of large error under small optical power is solved.

Description

Technical Field

[0001] This invention relates to the field of integrated circuit design technology, and more specifically, to an APC regulation circuit and method. Background Technology

[0002] In high-speed optical communication applications, data streams require laser driver circuits to convert electrical signals into optical signals, which are then transmitted along physical media such as optical fibers. The laser needs to be configured with an appropriate average optical power to operate at a suitable level and ensure the transmission quality of high-speed optical signals. The average optical power is also related to the fiber optic transmission distance; considering losses such as dispersion along the optical path, long-distance fiber optic transmission requires a relatively high optical power.

[0003] The average optical power of a laser is determined by the laser driver circuit. The laser driver circuit outputs a certain bias current I. BIAS Set the center operating point of the laser optical signal. Using a bias current I... BIAS Centered on the laser, the driving circuit converts the electrical modulation signal into a high-speed current signal. The current signal flows through the laser and is then converted into a high-speed optical signal, thus enabling the transmission of the optical signal.

[0004] In order to adaptively adjust the average optical power (AOP), traditional circuits typically employ an automatic power correction (APC) circuit. This involves monitoring the MPD diode current I. PD This reflects the average optical power of the laser LD. The current of the monitoring diode MPD flows through the transimpedance amplifier TIA, and the magnitude of the MPD current is extracted to obtain the current signal I. PD ', and then with reference current I REF Compare and adjust the output bias current I. BIAS The magnitude of the value is used to adjust the average optical power of the laser LD. Finally, during the steady-state adjustment of the loop, the diode MPD current and the reference current I are monitored. REF The average optical power of the laser is locked in a stable manner.

[0005] When the average optical power (AOP) is expressed in dBm, AOP dBm With reference current I REF The linear relationship between them is no longer maintained. A desired target optical power (AOP) needs to be set. dBm At that time, it is difficult to obtain the reference current I intuitively and quickly. REF What should it be set to? And in I... REF When the value is very small, the target optical power AOP dBm The change was drastic. Due to I REFCurrent deviation itself will cause the target optical power AOP to be affected. dBm Significant deviations can easily lead to low values ​​of target optical power AOP. dBm No. Summary of the Invention

[0006] This invention addresses the difficulty of obtaining the reference current I directly and quickly in traditional automatic optical power correction circuits. REF The set value results in a small target optical power AOP. dBm To address the inaccuracy issue, an APC adjustment circuit is proposed; a logarithmic converter circuit is used to replace the transimpedance amplifier TIA, thereby enabling the monitoring of the diode MPD current I. PD Extraction and monitoring of the diode MPD current I PD Logarithmic transformation; AOP of target optical power dBm The target monitoring diode MPD current is converted into a linear relationship, which is intuitive and convenient for debugging, and solves the problem of large error under low light power.

[0007] The specific implementation details of this invention are as follows:

[0008] An APC regulation circuit includes a monitoring diode, a laser, and a comparator; it also includes a logarithmic converter.

[0009] The input terminal of the logarithmic converter is connected to the monitoring diode, and the output terminal is connected to the second input terminal of the comparator.

[0010] The first input terminal of the comparator receives a reference current I. REF The output of the comparator is connected to the laser;

[0011] The logarithmic converter is used to logarithmically convert the monitoring diode MPD current I obtained from the monitoring diode. PD The logarithmically transformed output current I of the monitoring diode MPD is obtained. OUT ;

[0012] The comparator is used to compare the acquired reference current I. REF The output current I of the monitoring diode MPD after logarithmic conversion OUT Generate comparison results and dynamically adjust the bias current I based on the comparison results. BIAS ;

[0013] The laser is used to adjust the bias current I according to the dynamic adjustment. BIAS Adjust target optical power (AOP) dBm size.

[0014] To better realize the present invention, the logarithmic converter further includes an input unit, a differential unit, a first current mirror unit, and a second current mirror unit;

[0015] The first input terminal of the input unit is connected to the output terminal of the monitoring diode MPD, the second input terminal of the input unit receives the bias current, and the output terminal of the input unit is connected to the first input terminal of the differential unit.

[0016] The second input terminal of the differential unit is connected to the first current mirror unit, and the output terminal of the differential unit is connected to the input terminal of the second current mirror unit.

[0017] The output terminal of the second current mirror unit outputs the logarithmically converted monitoring diode MPD output current I. OUT .

[0018] To better realize the present invention, the input unit further includes transistor Q1 and transistor Q2;

[0019] The collector of transistor Q1 is connected to the output terminal of monitoring diode MPD, the base of transistor Q1 is connected between the collector of transistor Q1 and the output terminal of monitoring diode MPD, and the emitter of transistor Q1 is connected to ground.

[0020] The collector of transistor Q2 is fed with a bias current, the base of transistor Q2 is connected between the collector of transistor Q2 and the bias current, and the emitter of transistor Q2 is connected to ground.

[0021] The input terminal of the differential unit is connected between the base of the transistor Q1 and the output terminal of the monitoring diode MPD.

[0022] To better realize the present invention, the differential unit further includes transistor Q3, transistor Q4, resistor R0, resistor R1, resistor R2, and resistor R3;

[0023] One end of the resistor R0 is connected between the base of the transistor Q1 and the output terminal of the monitoring diode MPD, and the other end is connected to the base of the transistor Q3.

[0024] One end of the resistor R1 is connected between the resistor R0 and the base of the transistor Q3, and the other end is connected to the ground.

[0025] The collector of transistor Q3 is connected to the first current mirror unit, and the emitter of transistor Q3 is connected to ground.

[0026] The collector of transistor Q4 is connected between the first current mirror unit and the second current mirror unit, and the emitter of transistor Q4 is connected to the emitter of transistor Q3.

[0027] One end of the resistor R2 is connected to the base of the transistor Q4, and the other end is connected between the base and collector of the transistor Q2.

[0028] One end of the resistor R3 is connected between the base of the transistor Q4 and the resistor R2, and the other end is connected to ground.

[0029] To better realize the present invention, the first current mirror unit further includes MOS transistor M1 and MOS transistor M2;

[0030] The source of the MOS transistor M1 is connected to the power supply VDD, the gate of the MOS transistor M1 is connected to the drain of the MOS transistor M1, and the drain of the MOS transistor M1 is connected to the collector of the transistor Q3.

[0031] The gate of MOS transistor M2 is connected to the gate of MOS transistor M1, the source of MOS transistor M2 is connected to the power supply VDD, and the drain of MOS transistor M2 is connected to the collector of transistor Q4.

[0032] To better realize the present invention, the second current mirror unit further includes MOSFET M3 and MOSFET M4;

[0033] The drain of the MOS transistor M3 is connected between the drain of the MOS transistor M2 and the collector of the transistor Q4. The source of the MOS transistor M3 is connected to ground. The gate of the MOS transistor M3 is connected to the drain of the MOS transistor M3.

[0034] The gate of MOSFET M4 is connected to the gate of MOSFET M3, the source of MOSFET M4 is connected to the source of MOSFET M3 and ground, and the drain of MOSFET M4 outputs the logarithmically converted monitoring diode MPD current I. OUT .

[0035] Based on the APC adjustment circuit proposed above, in order to better realize the present invention, an APC adjustment method is further proposed, which is implemented based on the above APC adjustment circuit; specifically, it includes the following steps:

[0036] Step S1: Based on the obtained thermal voltage, bias current I1, and monitoring diode MPD current I... PD Calculate the voltage difference ΔVBE;

[0037] Step S2: Calculate the differential output current of the differential pair transistors Q3 and Q4 based on the voltage difference ΔVBE;

[0038] Step S3: Mirror the differential output current using the second current mirror unit to obtain the logarithmically converted output current I of the monitoring diode MPD. OUT ;

[0039] Step S4: Based on the monitoring diode MPD current I PD The relationship between average laser current and average optical power (AOP), and the relationship between average optical power (AOP) and target optical power (AOP). dBm The conversion relationship and differential output current are used to obtain the AOP (Average Power Optimum) relative to the target optical power. dBm Linearly correlated current output signal.

[0040] To better realize the present invention, step S1 further includes the following steps:

[0041] Step S11: Based on the obtained thermal voltage and the monitoring diode MPD current I... PD Calculate the reverse saturation current of transistor Q1 and its base voltage VBE1.

[0042] Step S12: Calculate the base voltage VBE2 of transistor Q2 based on the obtained thermal voltage, bias current I1, and reverse saturation current of transistor Q2.

[0043] Step S13: Calculate the voltage difference ΔVBE based on the base voltage VBE1 of transistor Q1 and the base voltage VBE2 of transistor Q2.

[0044] To better realize the present invention, step S2 further includes the following steps:

[0045] Step S21: Based on the voltage difference ΔVBE, obtain the input voltages of the differential pair transistors Q3 and Q4;

[0046] Step S22: Calculate the transconductance gm based on the tail current 2*I2 of the differential pair transistors Q3 and Q4;

[0047] Step S23: Calculate the differential output current of the differential pair based on the transconductance gm and the input voltages of the differential pair transistors Q3 and Q4.

[0048] To better realize the present invention, further, the target optical power AOP in step S4 is... dBm The linearly related current output signal is:

[0049] I OUT = K' * AOP dBm + C'

[0050] Where K' = K / 10, C' = C + K*lg(R*1mW);

[0051] K, K', C', and C are fixed parameters, and R is the responsivity of the monitoring diode MPD.

[0052] The present invention has the following beneficial effects:

[0053] This invention replaces the transimpedance amplifier (TIA) with a logarithmic converter to monitor the current I of the diode MPD. PD Extraction and monitoring of the diode MPD current I PD Logarithmic transformation; AOP of target optical power dBm The target monitoring diode MPD current is converted into a linear relationship, which is intuitive and convenient for debugging, and solves the problem of large error under low light power. Attached Figure Description

[0054] Figure 1 This is a schematic diagram of the laser circuit structure.

[0055] Figure 2 This is a graph showing the relationship between the laser's optical signal and current signal.

[0056] Figure 3 This is a circuit diagram for traditional average optical power correction.

[0057] Figure 4 This is a schematic diagram of the adjustment process of a traditional average optical power correction circuit.

[0058] Figure 5 For the target AOP in the traditional average optical power correction scheme dBm With reference current I REF The relationship curve between them.

[0059] Figure 6 This is a schematic diagram of the APC regulation circuit structure proposed in this invention.

[0060] Figure 7 A schematic diagram of the logarithmic converter circuit structure provided by the present invention. Detailed Implementation

[0061] To more clearly illustrate the technical solutions of the embodiments of the present invention, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. It should be understood that the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments, and therefore should not be regarded as a limitation on the scope of protection. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0062] In the description of this invention, it should be noted that, unless otherwise explicitly specified and limited, the terms "set up," "connected," and "linked" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; and they can refer to the internal connection of two components. Those skilled in the art can understand the specific meaning of the above terms in this invention based on the specific circumstances.

[0063] The structure of the laser is as follows Figure 1 As shown, the laser is a current-driven device, and the following relationship exists between optical power and current:

[0064] Power LD = h * (I LD - I TH (1)

[0065] Power LD is the laser's emitted light power, measured in W; h is the laser's slope efficiency parameter, measured in W / A; I LD I represents the current in the laser, measured in amperes (A). TH This represents the threshold current of the laser, measured in amperes (A). When the current I on the laser... LD Below the laser's threshold current I TH At this time, the laser does not emit light and is in the cutoff off state.

[0066] like Figure 2 The figure shows the relationship curve between the laser optical signal and the current signal. From the relationship (1), we can obtain I BIAS The current sets the average optical power (AOP) of the laser. The modulation signal "0" corresponds to a smaller current value I0, which corresponds to a smaller optical signal P0; the modulation signal "1" corresponds to a larger current value I1, which corresponds to a larger optical signal P1; the modulation signal bit stream is transmitted as optical signals of the data stream through the P1 and P0 optical signals emitted by the laser.

[0067] In practical applications, the luminous slope efficiency h and threshold current I of the laser TH Significantly affected by ambient temperature: the higher the ambient temperature, the higher the I TH The larger the value, the lower the value of h. This means that in high-temperature environments, a larger current signal is needed to convert it into a light signal.

[0068] To adaptively adjust the average optical power (AOP), the conventional approach is to design an automatic optical power correction circuit. This circuit typically follows a similar design. Figure 3 As shown.

[0069] Monitoring diode MPD current IPD This reflects the average optical power of the laser LD. The monitoring diode MPD current I... PD The current I flowing through the transimpedance amplifier TIA is extracted from the monitoring diode MPD. PD The magnitude is used to obtain the current signal I. PD ', and then with reference current I REF Compare and adjust the output bias current I. BIAS The magnitude of the value is used to adjust the average optical power of the laser LD. Finally, when the loop reaches steady state, the current I of the MPD diode is monitored. PD and reference current I REF When the values ​​are equal, the average optical power of the laser is stably locked. The adjustment process is as follows: Figure 4 As shown.

[0070] Monitoring diode MPD current I PD The following proportional relationship exists between the average current and average optical power (AOP) of the laser, where R is the responsivity of the monitoring diode (MPD), measured in A / W, and depends on the coupling coefficient between the MPD and the laser (LD).

[0071] I PD = AOP * R (2)

[0072] When the average optical power is stably locked in the above loop.

[0073] I REF = I PD (3)

[0074] The average optical power of the laser when it is stably locked is obtained:

[0075] AOP = I REF / R (4)

[0076] By setting I REF The magnitude of the current determines the target lock value for the laser's average optical power (AOP).

[0077] As can be seen from equation (5), the average optical power of the laser (in W) is related to the reference current I. REF There is a linear correlation between (unit: A) and (unit: A). However, in practical applications, laser optical power is usually expressed in dBm, and rarely in W. The following conversion relationship exists between dBm and W:

[0078] dBm = 10 * lg (Power LD / 1mW) (5)

[0079] Convert the average optical power (AOP) in W to the target optical power (AOP) in dBm.dBm ,get:

[0080] AOP dBm = 10*lg(AOP / 1mW) (6)

[0081] The target-locked average optical power obtained by automatic optical power correction using the above scheme, when expressed in dBm, is no longer linearly related to the reference current, as shown in the following equation:

[0082] AOP dBm = 10*lg ( I REF / R / 1mW) (7)

[0083] Clearly, when the average optical power (AOP) is expressed in dBm, AOP... dBm With reference current I REF The linear relationship between them is no longer maintained. A desired target optical power (AOP) needs to be set. dBm At that time, it is difficult to obtain the reference current I intuitively and quickly. REF What should it be set to? And in I... REF When the value is very small, AOP dBm The change was dramatic, such as Figure 5 As shown. Due to the reference current I REF Self-bias will cause target optical power AOP dBm Significant deviations can easily lead to low values ​​of target optical power AOP. dBm No.

[0084] Example 1:

[0085] This embodiment proposes an APC adjustment circuit, such as Figure 6 As shown, it includes a monitoring diode, a laser, and a comparator; it also includes a logarithmic converter;

[0086] The input terminal of the logarithmic converter is connected to the monitoring diode, and the output terminal is connected to the second input terminal of the comparator.

[0087] The first input terminal of the comparator receives a reference current I. REF The output of the comparator is connected to the laser;

[0088] The logarithmic converter is used to logarithmically convert the monitoring diode MPD current I obtained from the monitoring diode. PD The logarithmically transformed output current I of the monitoring diode MPD is obtained. OUT ;

[0089] The comparator is used to compare the acquired reference current I. REF The output current I of the monitoring diode MPD after logarithmic conversionOUT Generate comparison results and dynamically adjust the bias current I based on the comparison results. BIAS ;

[0090] The laser is used to adjust the bias current I according to the dynamic adjustment. BIAS Adjust target optical power (AOP) dBm size.

[0091] Working principle: This embodiment replaces the transimpedance amplifier (TIA) in the traditional average optical power correction circuit with a logarithmic converter to monitor the MPD current I. PD Extraction and monitoring of the diode MPD current I PD Logarithmic transformation of the target optical power AOP dBm The target monitoring diode MPD current is converted into a linear relationship, which is intuitive and convenient for debugging, and solves the problem of large error under low light power.

[0092] Example 2:

[0093] This embodiment is based on the above embodiment 1, such as... Figure 7 As shown, the structure of a logarithmic converter is described in detail with reference to a specific embodiment.

[0094] The logarithmic converter includes an input unit, a differential unit, a first current mirror unit, and a second current mirror unit;

[0095] The first input terminal of the input unit is connected to the output terminal of the monitoring diode MPD, the second input terminal of the input unit receives the bias current, and the output terminal of the input unit is connected to the first input terminal of the differential unit.

[0096] The second input terminal of the differential unit is connected to the first current mirror unit, and the output terminal of the differential unit is connected to the input terminal of the second current mirror unit.

[0097] The output terminal of the second current mirror unit outputs the logarithmically converted monitoring diode MPD output current I. OUT .

[0098] The input unit includes transistor Q1 and transistor Q2;

[0099] The collector of transistor Q1 is connected to the output terminal of monitoring diode MPD, the base of transistor Q1 is connected between the collector of transistor Q1 and the output terminal of monitoring diode MPD, and the emitter of transistor Q1 is connected to ground.

[0100] The collector of transistor Q2 is fed with a bias current, the base of transistor Q2 is connected between the collector of transistor Q2 and the bias current, and the emitter of transistor Q2 is connected to ground.

[0101] The input terminal of the differential unit is connected between the base of the transistor Q1 and the output terminal of the monitoring diode MPD.

[0102] The differential unit includes transistor Q3, transistor Q4, resistor R0, resistor R1, resistor R2, and resistor R3;

[0103] One end of the resistor R0 is connected between the base of the transistor Q1 and the output terminal of the monitoring diode MPD, and the other end is connected to the base of the transistor Q3.

[0104] One end of the resistor R1 is connected between the resistor R0 and the base of the transistor Q3, and the other end is connected to the ground.

[0105] The collector of transistor Q3 is connected to the first current mirror unit, and the emitter of transistor Q3 is connected to ground.

[0106] The collector of transistor Q4 is connected between the first current mirror unit and the second current mirror unit, and the emitter of transistor Q4 is connected to the emitter of transistor Q3.

[0107] One end of the resistor R2 is connected to the base of the transistor Q4, and the other end is connected between the base and collector of the transistor Q2.

[0108] One end of the resistor R3 is connected between the base of the transistor Q4 and the resistor R2, and the other end is connected to ground.

[0109] The first current mirror unit includes MOSFET M1 and MOSFET M2;

[0110] The source of the MOS transistor M1 is connected to the power supply VDD, the gate of the MOS transistor M1 is connected to the drain of the MOS transistor M1, and the drain of the MOS transistor M1 is connected to the collector of the transistor Q3.

[0111] The gate of MOS transistor M2 is connected to the gate of MOS transistor M1, the source of MOS transistor M2 is connected to the power supply VDD, and the drain of MOS transistor M2 is connected to the collector of transistor Q4.

[0112] The second current mirror unit includes MOSFET M3 and MOSFET M4;

[0113] The drain of the MOS transistor M3 is connected between the drain of the MOS transistor M2 and the collector of the transistor Q4. The source of the MOS transistor M3 is connected to ground. The gate of the MOS transistor M3 is connected to the drain of the MOS transistor M3.

[0114] The gate of MOSFET M4 is connected to the gate of MOSFET M3, the source of MOSFET M4 is connected to the source of MOSFET M3 and ground, and the drain of MOSFET M4 outputs the logarithmically converted monitoring diode MPD current I. OUT .

[0115] Working principle: such as Figure 7 The diagram shows a logarithmic converter circuit. Transistors Q1 and Q2 are NPN transistors of the same size. B1 is the base voltage of Q1, and B2 is the base voltage of Q2. VBE1 is the voltage difference between the base and emitter of Q1. VBE2 is the voltage difference between the base and emitter of Q2. The monitoring diode MPD current I... PD The current flows into the collector of transistor Q1. A fixed bias current I1 flows into the collector of transistor Q2. Resistors R0, R1, R2, and R3 are four resistors, where R0 and R2 have the same resistance, and R1 and R3 have the same resistance. The resistances of R1 and R0, and R3 and R2, maintain an M:1 ratio. POS transistors M1 and M2 are PMOS current mirrors of the same size, and NMOS transistors M3 and M4 are NMOS current mirrors of the same size. Transistors Q3 and Q4 form an NPN differential pair, with output currents I3 and I4, respectively. B3 and B4 are the base voltages of transistors Q3 and Q4, respectively, i.e., the differential input voltages of the differential pair. The tail current bias of the differential pair is 2*I2. OUT This is the output current of NMOS transistor M4, which is the output current of the logarithmic converter.

[0116] The other parts of this embodiment are the same as those in Embodiment 1 above, so they will not be described again.

[0117] Example 3:

[0118] This embodiment, based on any one of Embodiments 1-2 above, proposes an APC adjustment method, implemented using the aforementioned APC adjustment circuit; specifically, it includes the following steps:

[0119] Step S1: Based on the obtained thermal voltage, bias current I1, and monitoring diode MPD current I... PD Calculate the voltage difference ΔVBE;

[0120] Step S1 specifically includes the following steps:

[0121] Step S11: Based on the obtained thermal voltage and the monitoring diode MPD current I... PD Calculate the reverse saturation current of transistor Q1 and its base voltage VBE1.

[0122] Step S12: Calculate the base voltage VBE2 of transistor Q2 based on the obtained thermal voltage, bias current I1, and reverse saturation current of transistor Q2.

[0123] Step S13: Calculate the voltage difference ΔVBE based on the base voltage VBE1 of transistor Q1 and the base voltage VBE2 of transistor Q2.

[0124] Step S2: Calculate the differential output current of the differential pair transistors Q3 and Q4 based on the voltage difference ΔVBE;

[0125] Step S2 specifically includes the following steps:

[0126] Step S21: Based on the voltage difference ΔVBE, obtain the input voltages of the differential pair transistors Q3 and Q4;

[0127] Step S22: Calculate the transconductance gm based on the tail current 2*I2 of the differential pair transistors Q3 and Q4;

[0128] Step S23: Calculate the differential output current of the differential pair based on the transconductance gm and the input voltages of the differential pair transistors Q3 and Q4.

[0129] Step S3: Mirror the differential output current using the second current mirror unit to obtain the logarithmically converted output current I of the monitoring diode MPD. OUT ;

[0130] Step S4: Based on the monitoring diode MPD current I PD The relationship between average laser current and average optical power (AOP), and the relationship between average optical power (AOP) and target optical power (AOP). dBm The conversion relationship and differential output current are used to obtain the AOP (Average Power Optimum) relative to the target optical power. dBm Linearly correlated current output signal.

[0131] The target optical power AOP mentioned in step S4 dBm The linearly related current output signal is:

[0132] I OUT = K' * AOP dBm + C'

[0133] Where K' = K / 10, C' = C + K*lg(R*1mW);

[0134] K, K', C', and C are fixed parameters, and R is the responsivity of the monitoring diode MPD.

[0135] Working principle: This embodiment first uses the current-voltage formula of an NPN transistor to obtain...

[0136] VBE1 = VT*ln(I PD / I S1 (8)

[0137] VBE2 = VT*ln(I1 / I S2 (9)

[0138] Where VT is the thermodynamic voltage, which is 26mV at room temperature and is proportional to the thermodynamic voltage. S1 I is the reverse saturation current of transistor Q1. S2 represents the reverse saturation current of transistor Q2, and both are device-related characteristic parameters. ln is the natural logarithm function with the natural constant e as the base.

[0139] Since transistors Q1 and Q2 have the same dimensions, then:

[0140] I S1 = I S2 (10)

[0141] From equations (8)-(10), we get:

[0142] ΔVBE = VBE1 – VBE2 = VT*ln(I PD / I1) (11)

[0143] A 1:(M+1) voltage divider resistor is formed between R0 and R1, and between R2 and R3. The input voltages of the differential pair transistors Q3 and Q4 are then obtained as follows:

[0144] B3 - B4 = ΔVBE / (1+M) (12)

[0145] Differential pair transistors Q3 and Q4 are biased by the tail current 2*I2, and their transconductance gm is:

[0146] gm = I² / VT (13)

[0147] The differential output current of the differential pair is:

[0148] I3– I4= gm * (B3 – B4) (14)

[0149] From equations (11)-(14), the differential output current of the differential pair is obtained as follows:

[0150] I3– I4 = I2 / VT * VT*ln(I PD / I1) / (1+M) = I2 / (1+M) * ln(I PD / I1) (15)

[0151] In the differential output current expression of the differential pair, the thermal voltage VT is eliminated, and I3–I4 are independent of temperature.

[0152] The differential output current of the differential pair is then mirrored by current mirrors M3 and M4 to obtain the output current of the logarithmic converter, which is the output current I of the monitoring diode MPD after logarithmic conversion. OUT for:

[0153] I OUT = I² / (1+M) * ln(I PD / I1) (16)

[0154] The conversion formula between the natural logarithm and the lg function with base 10 is as follows:

[0155] ln(x) = lg(x) / lg(e) (17)

[0156] Then I OUT It can be represented as:

[0157] I OUT = I² / (1+M) / lg(e) * lg(I) PD / I1) (18)

[0158] Since I2, M, I1, and lg(e) are all fixed parameters, independent of environmental and optical power changes, the above equation can be transformed into:

[0159] I OUT = K * lg(I PD ) + C (19)

[0160] Here, K and C are fixed parameters that do not depend on changes in the environment or optical power.

[0161] K = I² / (1+M) / lg(e) (20)

[0162] C = -K * lg(I1) (21)

[0163] Combining equations (2), (6), and (19), we obtain

[0164] I OUT = K' * AOP dBm + C' (22)

[0165] in,

[0166] K' = K / 10 (23)

[0167] C' = C + K*lg(R*1mW) (24)

[0168] As can be seen from equation (22), the logarithmic converter circuit can obtain a value similar to that of the AOP. dBm Linearly correlated current output signal. Figure 6 In the laser automatic optical power correction circuit shown, this output current I OUT With reference current I REF Compare the magnitudes and dynamically adjust the bias current I. BIAS The current magnitude adjusts the laser's optical power. In steady-state lockout, the output current I... OUT and reference current I REF The currents are equal. Unlike traditional methods, the I here... OUT It is AOP dBm Linear correspondence, adjust the reference current I REF The size adjusts the target optical power AOP. dBm The numerical value is direct and convenient. Furthermore, there is no reference current I under different optical power controls. REF The accuracy requirements are different.

[0169] The other parts of this embodiment are the same as any one of the above embodiments 1-2, so they will not be described again.

[0170] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention in any way. Any simple modifications or equivalent changes made to the above embodiments based on the technical essence of the present invention shall fall within the protection scope of the present invention.

Claims

1. An APC regulation circuit, comprising a monitoring diode, a laser, and a comparator; characterized in that, It also includes a logarithmic converter; The input terminal of the logarithmic converter is connected to the monitoring diode, and the output terminal is connected to the second input terminal of the comparator. The first input terminal of the comparator receives a reference current I. REF The output of the comparator is connected to the laser; The logarithmic converter is used to logarithmically convert the monitoring diode MPD current I obtained from the monitoring diode. PD The logarithmically transformed output current I of the monitoring diode MPD is obtained. OUT ; The comparator is used to compare the acquired reference current I. REF The output current I of the monitoring diode MPD after logarithmic conversion OUT Generate comparison results and dynamically adjust the bias current I based on the comparison results. BIAS ; The laser is used to adjust the bias current I according to the dynamic adjustment. BIAS Adjust target optical power (AOP) dBm size; The logarithmic converter includes an input unit, a differential unit, a first current mirror unit, and a second current mirror unit; The first input terminal of the input unit is connected to the output terminal of the monitoring diode MPD, the second input terminal of the input unit receives the bias current, and the output terminal of the input unit is connected to the first input terminal of the differential unit. The second input terminal of the differential unit is connected to the first current mirror unit, and the output terminal of the differential unit is connected to the input terminal of the second current mirror unit. The output terminal of the second current mirror unit outputs the logarithmically converted monitoring diode MPD output current I. OUT ; The input unit includes transistor Q1 and transistor Q2; The collector of transistor Q1 is connected to the output terminal of monitoring diode MPD, the base of transistor Q1 is connected between the collector of transistor Q1 and the output terminal of monitoring diode MPD, and the emitter of transistor Q1 is connected to ground. The collector of transistor Q2 is fed with a bias current, the base of transistor Q2 is connected between the collector of transistor Q2 and the bias current, and the emitter of transistor Q2 is connected to ground. The input terminal of the differential unit is connected between the base of the transistor Q1 and the output terminal of the monitoring diode MPD; The differential unit includes transistor Q3, transistor Q4, resistor R0, resistor R1, resistor R2, and resistor R3; One end of the resistor R0 is connected between the base of the transistor Q1 and the output terminal of the monitoring diode MPD, and the other end is connected to the base of the transistor Q3. One end of the resistor R1 is connected between the resistor R0 and the base of the transistor Q3, and the other end is connected to the ground. The collector of transistor Q3 is connected to the first current mirror unit, and the emitter of transistor Q3 is connected to ground. The collector of transistor Q4 is connected between the first current mirror unit and the second current mirror unit, and the emitter of transistor Q4 is connected to the emitter of transistor Q3. One end of the resistor R2 is connected to the base of the transistor Q4, and the other end is connected between the base and collector of the transistor Q2. One end of the resistor R3 is connected between the base of the transistor Q4 and the resistor R2, and the other end is connected to ground. The first current mirror unit includes MOSFET M1 and MOSFET M2; The source of the MOS transistor M1 is connected to the power supply VDD, the gate of the MOS transistor M1 is connected to the drain of the MOS transistor M1, and the drain of the MOS transistor M1 is connected to the collector of the transistor Q3. The gate of the MOS transistor M2 is connected to the gate of the MOS transistor M1, the source of the MOS transistor M2 is connected to the power supply VDD, and the drain of the MOS transistor M2 is connected to the collector of the transistor Q4. The second current mirror unit includes MOSFET M3 and MOSFET M4; The drain of the MOS transistor M3 is connected between the drain of the MOS transistor M2 and the collector of the transistor Q4. The source of the MOS transistor M3 is connected to ground. The gate of the MOS transistor M3 is connected to the drain of the MOS transistor M3. The gate of MOSFET M4 is connected to the gate of MOSFET M3, the source of MOSFET M4 is connected to the source of MOSFET M3 and ground, and the drain of MOSFET M4 outputs the logarithmically converted monitoring diode MPD current I. OUT .

2. An APC adjustment method, implemented based on the APC adjustment circuit as described in claim 1; characterized in that, Specifically, the following steps are included: Step S1: Based on the obtained thermal voltage, bias current I1, and monitoring diode MPD current I... PD Calculate the voltage difference ΔVBE; Step S2: Calculate the differential output current of the differential pair transistors Q3 and Q4 based on the voltage difference ΔVBE; Step S3: Mirror the differential output current using the second current mirror unit to obtain the logarithmically converted output current I of the monitoring diode MPD. OUT ; Step S4: Based on the monitoring diode MPD current I PD The relationship between average laser current and average optical power (AOP), and the relationship between average optical power (AOP) and target optical power (AOP). dBm The conversion relationship and differential output current are used to obtain the AOP (Average Power Optimum) relative to the target optical power. dBm Linearly correlated current output signal.

3. The APC adjustment method according to claim 2, characterized in that, Step S1 specifically includes the following steps: Step S11: Based on the obtained thermal voltage and the monitoring diode MPD current I... PD Calculate the reverse saturation current of transistor Q1 and its base voltage VBE1. Step S12: Calculate the base voltage VBE2 of transistor Q2 based on the obtained thermal voltage, bias current I1, and reverse saturation current of transistor Q2. Step S13: Calculate the voltage difference ΔVBE based on the base voltage VBE1 of transistor Q1 and the base voltage VBE2 of transistor Q2.

4. The APC adjustment method according to claim 3, characterized in that, Step S2 specifically includes the following steps: Step S21: Based on the voltage difference ΔVBE, obtain the input voltages of the differential pair transistors Q3 and Q4; Step S22: Calculate the transconductance gm based on the tail current 2*I2 of the differential pair transistors Q3 and Q4; Step S23: Calculate the differential output current of the differential pair based on the transconductance gm and the input voltages of the differential pair transistors Q3 and Q4.

5. The APC adjustment method according to claim 4, characterized in that, The target optical power AOP mentioned in step S4 dBm The linearly related current output signal is: I OUT =K’*AOP dBm +C’ Where K' = K / 10, C' = C + K*lg(R*1mW); I OUT The output current of the monitoring diode MPD after logarithmic conversion; K, K', C', and C are fixed parameters, and R is the responsivity of the monitoring diode MPD.

Images