铌酸锂光开关的驱动电路的研究

Design of Driving Circuit of Lithium NiobateSwitchWeimin Wang Huifeng BaiSchool of Telecommunication EngineeringBeijing University of Posts & Telecommunications,Beijing, PRC 100876baihuifeng@ wwmfly@AbstractDesign of the driving circuit of lithium niobate optical switch is proposed. Introducethe function and framework of the circuit. Some key electronic characteristics whichdefine the performance of the circuit are solved in this design such as the operatingvoltage, the switching speed. The design also provides steady high voltageperformance and protective measures. The experimental results show the maximumRepetition Rate of this circuit is 20 kHz. The output voltage is between 338 to 418V..Keywords:driving circuit; high- voltage; lithium niobate switch; matrix1IntroductionB Lithium niobate switch is seen as key elements for the development of OBS network [1] and other broadband communication for its high switching speed. The bottleneck for its progress is not only in optical dimension, but also in the electrical driving circuit. The major trouble of the driving circuit is high voltage and high switching speed. The driving voltage of lithium niobate switch is around 350V to 420V [2], therefore, there must be a driving circuit, which can work safely at this situation. The difficulty of the driving circuit is not only the high driving voltage, but also the large transient current for driving the lithium niobate switch which is a capacitive load to this circuit. If the driving circuit can’t sustain such transient current, the rising edge of the control signal turns bad and the switching speed turns down. The other trouble is the stability of the circuit. For the high voltage and large current, there must be a steady circuit. We designed a circuit which can drive three switches independent at the same time. It overcame the difficulties that mentioned before, and can work steady at a high switching speed. 2Architecture of the Driving CircuitFig. 1 Configuration of a 4×4 non-blocking switch matrixFig. 1 shows the configuration of a 4×4 non-blocking switch matrix [2]. The OSW, showed in thecloud, is a 1×2 lithium niobate switch. It is the load of the drive circuit, which is equivalent to a capacitance (75pF) [3]. Each Sub-board can achieve a 1×4 switch, which is composed of three OSW. MUX needs no electric operation, which is a passive optical component. To simplify the whole structure, every three OSWs, as showed in dotted line, used a same drive circuit. There were three parts in this circuit: Low-voltage Unit (LU), High-voltage driving Unit (HU) and Adjusting Unit (AU).Fig. 2 Function Block of Circuit2.1 The LULU achieved all logic mapping. It received routing signal from another board, and changes it into a control signal to operate HU. The disadvantage of this simple model is that there were no protections against logic errors. For the first reason, the MOSEFT, used in HU, can’t be working under high-voltage for a long time [4]. The second reason is that a wrong routing signal may lead to a wrong operation of the HU. As the structure of the system, at the most, there will be only two OSW working at the same time. When the wrong operation cause three working at the same time, it’s no only lead huge power dissipation, but also can damage the MOSEFT used in HU. To overcome this disadvantage, there is a protection. First, a counter added into the system. It starts to work, when a routing signal was received. When it counts to 200ns, no matter if there is routing signal or not, theLU will terminate to translate control signal and HU will be back into the initialization. So the MOSEFT can be protected against a over-time used. To overcome the second disadvantage, there need a truth table to detect which routing information is true and which operation should be prohibited. As there were four similar parts in the system, there may be need four different truth table. But, if there four different departments were designed, there may not only increase the logic resource, but also lead to a potential risk, that there were four similar but different parts, it is difficult to distinguish and if one of them can’t work, the others can’t substitute it for the diversity of the truth table. Boolean can be used to overcome the question. To use Boolean, the routing signal must be designed elaborately, so the Boolean operation of routing signal can be used to predigest the logic.B VDSS (V) R DS(ON) (ohm) I D(ON)C ISS (pF)C RSS (pF)DEVICE TN2540 TP2540 Min400-400Typ Max8.0 12.020.0 30.0Min0.3-0.2Typ Max95 12560 125Typ Max102510 25BV DSS = Drain-to-Source Breakdown Voltage C IN = Input Capacitance of whole HUC ISS = Input Capacitance of MOS C RSS = Reverse Transfer CapacitanceI D(ON)=ON-State :Drain Current R DS(ON)= Static Drain-to-Source ON-State ResistanceTable 1 Electrical Characteristics of TN2540 and TP2540[4]2.2 The HUThe HU is the part that work under a high voltage and switch at a high speed. As the diversity of the OSW, the work voltage of HU is around 420V to 330V. And to satisfy the Burst-length, the switching speed –raising edge of control signal —must be restricted less then 100ns[5]. The circuit, showed in Fig.3, can implement this function. It is the output stage of all this system and consists of low threshold DMOS discrete transistors TP2540N3 and TN2540N3 [4]. These devices have a breakdown voltage rating of 400V minimum. Output voltage swings can switch from 0V to 400V. Input capacitance is increased due to Miller effect, C IN = C ISS + C RSS (G FS* R L). Low C RSS & C ISS capacitance, high output current, low on-resistance and 400V breakdown voltage are requiredparameters for the output transistors. The TP2450N3 and TN2450N3 are ideally suited these requirement. Their parameters are listed in Table 1.During power up and power down conditions, it is possible for transient voltages greater than 20V to appear across the gate-to-source on the output transistors. Maximum gate-to-source voltage, V GS , is rated at ±20V . 15V zener diodes are connected across the gate and source of the output transistors to protect against such transient voltages. These diodes will not be zenering during normal operation. Fig 4 shows the operate voltage (Repetition Rate is 20 KHz). In the test, we use fixed frequency square-wave to simulate the Burst. The test result showed that the highest Repetition Ratewas 20 KHz.Fig.3 The High-voltge driving Unit (HU) Fig.4. 50 usec Output Pulse2.3 The AUThe kernel element of AU is the positive voltage adjustable regulator. It is easy to use for the reliability. But the output voltage range (around 40V) of the regulator is too limited to suit the requirement of 300V to 400V for this circuit. So, there must be a new type of design to meet the requirement. Fig 5 showed the typical use of the regulator.Fig 5 The typical use of the regulatorFig 6 The Adjusting Unit circuit (AU)There is a norm voltage between Adjust Pin and the Output Pin and the Output V oltage is V OUT [6].⎟⎟⎠⎞⎜⎜⎝⎛+×=12125.1R R V OUT The adjustability is achievement for modulating the R 2. The Input–Output V oltage Differential must be limited between 1.5V and 25V . To content the high-voltage requirement, therefore, there is an expansion to the input circuit. As it is showed in Fig 6, a zener was added between B and D. It confirms that the voltage differential between B and D was kept in a constant value, no matter the input change out of the range or not. So it can confirm the Input–Output V oltage Differential constant. 7.01−=−DZ OUT IN V V V . V DZ1, here, is the Reverse V oltage of zener diode and its value is 6.3V . So, )(8.57.03.6V V V OUT IN =−=−. The voltage higher then (V OUT +5.8V) in input voltage was consumed on Q (a power transistor). For the minimum V OUT is 350V and the voltage at A is 600V , the transistor Q must endures a voltage V AC :)(2.244)8.5350(600V V AC =+−=So the power transistor used here is BU326. The Collector-Emitter Sustaining V oltage of BU326 is 400V . The new design of the output circuit is to add tree zeners to expend the output voltage range. The voltage on R4 is (V DZ2+V DZ3+V DZ4 +1.25V). So the new norm voltage is (V DZ2 +V DZ3+V DZ4 +1.25V). The Reverse V oltage of D2, D3 and D4 were 80V . So the V OUT can be expended to: )1(5.241)1)(25.1(465465432R R R R R R V V V V DZ DZ DZ OUT ++×=+++++= R5 is a rheostat from 0 t o10 kohm. The value of R4 and R6 is 30k and 12k. So the range of V OUT V is 338.1 to 418.6. Totally achieve the work requirement of lithium niobate optical switch.3 Experiment Results and ConclusionIn this paper, a whole set of driving circuit for lithium niobate optical switch is proposed. The layout of driving circuit is showed in Fig7. Compared with traditional circuit, it can increase the generality (for the huge adjustability of the high-voltage) and simplify the structure of the complete circuit. The result of the experiment shows that it can work safely for 3 hours and the float of the output voltage is less then 3V.Fig 7 The layout of driving circuit References[1] A. C. O'Donnell, N. J. Parsons, "1×16 lithium niobate optical switch matrix with integral TTL compatible drive electronics" Electronics Letters, vol. 27, Issue 25, pp.2367-2368, Dec. 1991[2]C. Qiao and M. Yoo, “Optical burst switching (OBS) – A new paradigm for an optical internet,” J. High Speed Networks, vol. 8, no. 1, pp. 69-84, 1999.[3] www. [4] [5] M. Yoo, M. Jeong, and C. Qiao, “A high speed protocol for bursty traffic in optical networks, in SPIE proceedings,” All Optical Communication Systems: Architecture, Control and Network issues, vol. 3230, pp.79-90, Nov. 1997.[6]N. R. Malik. Electronics Circuits — Analysis Simulation and Design. Prentice Hall, 1995。