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HFCT-5208M Datasheet(PDF) 3 Page - Agilent(Hewlett-Packard) |
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HFCT-5208M Datasheet(HTML) 3 Page - Agilent(Hewlett-Packard) |
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3 / 21 page  2 Figure 1. Relative Input Optical Power - dBm Average. 10-2 10-3 10-4 10-5 10-6 10-7 10-8 10-9 10-10 10-11 10-12 10-13 10-14 10-15 -5 LINEAR EXTRAPOLATION OF 10-4 THROUGH 10-7 DATA ACTUAL DATA -4 -3 -2 -1 0 12 3 Receiver Section The receiver contains an InGaAs PIN photodiode mounted together with a custom, silicon bipolar transimpedance preamplifier IC in an OSA. This OSA is mated to a custom, silicon bipolar circuit providing post amplification and quantization and optical signal detection. The custom, silicon bipolar circuit includes a Signal Detect circuit which provides a PECL logic high state output upon detection of a usable input optical signal level. This single-ended PECL output is designed to drive a standard PECL input through normal 50 W PECL load. Applications Information Typical BER Performance of HFBR-5208M Receiver versus Input Optical Power Level The HFBR/HFCT-5208M transceiver can be operated at Bit-Error-Ratio conditions other than the required BER = 1 x 10-10 of the 622 MBd ATM Forum 622.08 Mb/s Physical Layer Standard and the ANSI T1.646a. The typical trade-off of BER versus Relative Input Optical Power is shown in Figure 1. The Relative Input Optical Power in dB is referenced to the Input Optical Power parameter value in the Receiver Optical Characteristics table. For better BER condition than 1 x 10-10, more input signal is needed (+dB). For example, to operate the HFBR-5208M at a BER of 1 x 10-12, the receiver will require an input signal approximately 0.6 dB higher than the -26 dBm level required for 1 x 10-10 operation, i.e. -25.4 dBm. An informative graph of a typical, short fiber transceiver link per- formance can be seen in Figure 2. This figure is useful for designing short reach links with time-based jitter requirements. This figure indicates Relative Input Optical Power versus Sampling Time Position within the receiver output data eye-opening. The given curves are at a constant bit- error-ratio (BER) of 10-10 for four different signaling rates, 155 MBd, 311 MBd, 622 MBd and 650 MBd. These curves, called “tub” diagrams for their shape, show the amount of data eye-opening time-width for various receiver input optical power levels. A wider data eye-opening provides more time for the clock recovery circuit to operate within without creating errors. The deeper the tub is indicates less input optical power is needed to operate the receiver at the same BER condition. Generally, the wider and deeper the tub is the better. The Relative Input Optical Power amount (dB) is referenced to the absolute level (dBm avg.) given in the Receiver Optical Characteristics table. The 0 ns sampling time position for this Figure 2 refers to the center of the Baud interval for the particular signaling rate. The Baud interval is the reciprocal of the signaling rate in MBd. For example, at 622 MBd the Baud interval is 1.61 ns, at 155 MBd the Baud interval is 6.45 ns. Test conditions for this tub diagram are listed in Figure 2. The HFBR/HFCT-5208M receiver input optical power requirements vary slightly over the signaling rate range of 20 MBd to 700 MBd for a constant bit-error-ratio (BER) of 10-10 condition. Figure 3 illustrates the typical receiver relative input optical power varies by <0.7 dB over this full range. This small sensitivity variation allows the optical budget to remain nearly constant for designs that make use of the broad signaling rate range of the HFBR/HFCT-5208M. The curve has been normalized to the input optical power level (dBm avg.) of the receiver for 622 MBd at center of the Baud interval with a BER of 10-10. The data patterns that can be used at these signaling rates should be, on average, balanced duty factor of 50%. Momentary excursions of less or more data duty factor than 50% can occur, but the overall data pattern must remain balanced. Unbalanced data duty factor will cause excessive pulse-width distortion, or worse, bit errors. The test conditions are listed in Figure 3. Recommended Circuit Schematic When designing the HFBR/HFCT- 5208M circuit interface, there are a few fundamental guidelines to follow. For example, in the Recommended Circuit Schematic, Figure 4, the differential data lines should be treated as 50 ohm Microstrip or stripline transmission lines. This will help to minimize the parasitic inductance and capacitance effects. Proper termination of the differential data signal will prevent reflections and ringing which would compromise the signal fidelity and generate unwanted electrical noise. Locate termination at the received signal end of the transmission line. The length of these lines should be kept short and of equal length to prevent pulse-width distortion from occurring. For the high-speed signal lines, differential signals should be used, not single-ended signals. These differential signals need to be loaded symmetrically to prevent unbalanced currents from flowing which will cause distortion in the signal. |
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