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OQ2545BHP Datasheet(PDF) 11 Page - NXP Semiconductors |
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OQ2545BHP Datasheet(HTML) 11 Page - NXP Semiconductors |
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11 / 28 page  1999 Aug 24 11 Philips Semiconductors Product specification SDH/SONET STM16/OC48 laser drivers OQ2545HP; OQ2545BHP RF connections A coupled stripline or microstrip with an odd mode characteristic impedance of 50 Ω (nominal value) should be used for the differential RF connections on the PCB. This applies to the CML differential line pairs on pins CIN and CINQ, DIN and DINQ, CLOOP and CLOOPQ, DLOOP and DLOOPQ, and MON and MONQ. In addition, the following lines should not differ in length by more than 10 mm: • Lines to pins DIN, DINQ, CIN and CINQ • Lines to pins CLOOP, CLOOPQ, DLOOP and DLOOPQ. ESD protection In order to achieve high frequency performance, it has been necessary to make adjustments to the standard ESD protection scheme. Inputs on pins DIN, DINQ, CIN, CINQ, DLOOP, DLOOPQ, CLOOP and CLOOPQ and outputs on pins MON and MONQ are protected by a reduced ESD structure. The outputs on pins LA and LAQ have no protection against ESD, so extra care should be taken with these pins. Power consumption The total power consumption of the OQ2545(B)HP depends strongly on the application. A rough guideline is given to estimate the power consumption for a specific application. The total power dissipation (Ptot) consists of the following terms: Ptot =PVEE1 +PVCC +PVEE2 − (PLA +PLAQ +PIBIAS) where 1. PVEE1 and PVCC represent the power consumption terms corresponding with the supplies VEE1 and VCC, required for the digital section and the TTL interfaces. These 2 terms are application independent and only depend on the process spread and supply voltages. Values can be found in Chapter “Characteristics”. 2. PVEE2 =IEE2 ×VEE2 represents the power consumption of the analog section, including the modulation current and bias current. It is mainly determined by the magnitude of the modulation current and bias current and the additional biasing currents of the preamplifier and emitter followers. The supply current is the summation: IEE2 =55mA+1.5 × Imod +IIBIAS +3 × IAMPADJ +55 × IEFADJ where IAMPADJ and IEFADJ are the currents through pins AMPADJ and EFADJ, respectively. These figures are valid for nominal supply voltage and temperature and are given for rough indication only. 3. PLA, PLAQ and PIBIAS represent the dissipation in the external load (laser or EAM), caused by the modulation and bias current. The expressions are: PLA = 0.5 × ILA(ext) ×VLA, PLAQ = 0.5 × ILAQ(ext) ×VLAQ and PIBIAS =IIBIAS ×VIBIAS. The factor 0.5 represents the fact that, for a (scrambled) random data pattern, the modulation switch will be switched to either side 50% of the time integrated over many cycles. VLA and VLAQ are the voltages on pins LA and LAQ when the modulation current flows through pins LA and LAQ, respectively and the values depend on the external laser or EAM supply voltage, the forward diode voltage drop and additional loads. To increase the dissipation in the external load and thereby decreasing the dissipation in the IC, the values of VLA or VLAQ can be increased by adding additional external resistors. A minimum value of VLA and VLAQ is required for proper operation of the IC. A similar argument is valid for power consumption due to the bias current. It should be noted that this is important, because it provides an easy way to lower the power dissipation of the IC. Example Consider the following example to illustrate the calculation of Ptot. A laser diode operates at 0.3 mW (optical low) and 3 mW (optical high), i.e. an extinction ratio of 10 dB. For this laser type this requires IBIAS = 20 mA and ILA(ext) = 40 mA (see Fig.8). The series resistance of the laser is 30 Ω. Therefore the ratio is: Consequently, a total Imod = (130/100) × 40 = 52 mA will be generated by the IC. The impedance connected to pin LAQ is 30 Ω as well. As a result also ILAQ(ext) = 40 mA and ILAQ(int) =12mA (see Fig.9). In first instance the eye pattern is of adequate quality and the preamplifier and emitter follower do not need additional bias current, i.e. pins AMPADJ and EFADJ can be left open-circuit. I LA int () I LA ext () ------------------ 30 100 ---------- = |
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