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ISL59960IRZ データシート(PDF) 10 Page - Intersil Corporation |
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ISL59960IRZ データシート(HTML) 10 Page - Intersil Corporation |
10 / 17 page ISL59960 10 FN8358.0 December 18, 2012 Application Information Unshielded Twisted Pair (UTP) Application Circuit Figure 9 shows the complete schematic for a 960MegaQ™ equalizer configured for unshielded twisted pair (UTP) cable. The input signal is terminated into the network formed by R1, R2, and R3. C1 and C2 AC-couple the signal into 960MegaQ™. To protect the front-end circuitry, 5V transorbs (Z1 and Z2) should be used instead of diodes because the signals on either differential input may swing far enough below ground to turn on a diode and distort the video. On the output side, C5, R5, and C4 form a compensation network, while R6 provides 75Ω source-termination for the video output. 960MegaQ™ has an native gain of 6dB, so when VIDEO OUT is terminated into 75Ω (the input to a DVR, TV, etc.), R6 and the 75Ω terminator form a 2:1 divider, producing standard video amplitude across the 75Ω terminator. Coax Input Circuit Figure 10 shows the input termination recommended for coaxial cables. The differential termination resistance is now 75Ω to match the characteristic impedance of the RG-59 coax cable. C3 bypasses high-frequency noise on the coax ground line to system ground. This allows the coax ground to be independent of the system at low frequencies (DC to 50/60Hz) to accommodate differences in the ground potential of the remote video source(s). The coax startup network (D1, R4, C4) prevents a rare start-up condition that can occur when a high average-picture-level (e.g., white screen) video signal is present on the inputs before the power has been applied. Dual UTP/Coax Input Circuit If desired, it is also possible to support both UTP and coax cables with the same PCB layout using two SPST switches that are closed when in coax mode (Figure 11). Since UTP requires a 100Ω termination network while coax requires 75Ω, a switch to introduce a shunt 300Ω resistor when in coax mode will change the termination from 100Ω to 75Ω. A second switch is required to engage C3. The addition of the coax startup circuit (D1, R4, C4) can unbalance the capacitance of the differential pair and degrade the CMRR in UTP applications. This in turn could cause excess noise at long lengths of UTP. In UTP applications, if the output signal is too noisy at long distances, an optional capacitor Cx may be used to balance the capacitance of the differential inputs. The value of Cx should be determined by calculating how much trace capacitance is added by the coax startup circuit. A typical value for a good layout is ~5pF. Note that only coax or UTP should be connected at any one time - this circuit does not multiplex between them. Using the ISL59960 with Steel Core Coax Although the ISL59960 was designed for copper based cables, it is capable of equalizing signals for coaxial applications that use steel core cabling. Due to the higher DC and low-band resistance of this cable type, the ISL59960 will not equalize to the same distance as copper based cables. See Table 1 on page 9 for maximum equalization distances. Input Multiplexing Placing a semiconductor multiplexer in front of this part may increase high frequency attenuation and noise. However, a low-capacitance mechanical relay may be acceptable. Note that changing from one channel to another in Lock Until Reset mode will require a reset (INVERT toggle) to trigger equalization of the new channel (see “Lock Until RESET” on page 10). For best performance, do not multiplex the inputs to the equalizer - this can further degrade the signal. Instead, multiplex at the output after equalization has been performed. Stand-Alone Operation and Configuration In its default stand-alone configuration, 960MegaQ™ features two modes of automatic cable equalization: Lock Until Reset and Continuous Update. Lock Until Reset is the recommended mode for most applications. LOCK UNTIL RESET In the Lock Until Reset mode, once 960MegaQ™ finds the optimum equalization and the LOCKED signal goes high, the equalization is frozen and will not change until either the power is cycled or the INVERT signal is toggled, which initiates a re-equalization of the input signal. Re-equalization is usually only necessary during device/system evaluation - in normal operation 960MegaQ™ powers-up, acquires and equalizes the signal, and continues to equalize until/unless it is powered-down. If the signal is lost in Lock Until Reset mode, the LOCKED pin will not FIGURE 10. APPLICATION CIRCUIT FOR COAX CABLE IN- GND IN+ 1.0µF 37.5 Ω 1k Ω 1.0µF 37.5 Ω 0.1µF VCC 0.1µF 10k Ω 960MegaQTM R1 R2 R3 C1 C2 C3 R4 C4 D1 5V TVS Z2 Z1 5V TVS TVS = Transient Voltage Suppressor a.k.a. Transorb FIGURE 11. APPLICATION CIRCUIT FOR UTP/COAX CABLE IN- GND IN+ 1.0µF 49.9 Ω 1k Ω 1.0µF 49.9 Ω 0.1µF VCC 0.1µF 10k Ω 960MegaQTM 300 Ω Close all switches for Coax R1 R2 R3 C1 C2 C3 R4 C4 D1 SW1A R5 SW1B 5V TVS Z2 Z1 5V TVS UTP IN+ UTP IN- COAX Cx* *optional 5.6pF TVS = Transient Voltage Suppressor a.k.a. Transorb |
同様の部品番号 - ISL59960IRZ |
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同様の説明 - ISL59960IRZ |
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