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AD8322-EVAL Arkusz danych(PDF) 9 Page - Analog Devices |
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AD8322-EVAL Arkusz danych(HTML) 9 Page - Analog Devices |
9 / 16 page REV. 0 AD8322 –9– in an adjacent channel which could be occupied by a carrier of the same or different symbol rates.” Figure 7 shows the measured ACP, for a 16 QAM, 60 dBmV signal, taken at the output of the AD8322 evaluation board (see Figure 13 for evaluation board schematic). The transmit channel width and adjacent channel width in Figure 7 correspond to symbol rates of 160 KSYM/SEC. Table II shows the ACP results for the AD8322 for all conditions in DOCSIS Table 4-7 “Adjacent Channel Spurious Emissions.” –10 –20 –30 –40 –70 –50 –60 –80 CENTER 10MHz 60kHz SPAN 600kHz CL1 C0 C0 CU1 CL1 RBW 500Hz RF ATT 40dB VBW 5kHz SWT 12s UNIT dBm CH PWR 5.39dBm ACP UP –54.22dB ACP LOW –56.84dB F1 CU1 Figure 7. Adjacent Channel Power Table II. ACP Performance for All DOCSIS Conditions (All Values in dBc) TRANSMIT CHANNEL SYMBOL RATE 2560 KSYM/SEC –54.2 160 KSYM/SEC 320 KSYM/SEC 640 KSYM/SEC 1280 KSYM/SEC 2560 KSYM/SEC ADJACENT CHANNEL SYMBOL RATE –54.7 –55.4 –53.8 –54.6 –54.6 –54.0 –54.1 –54.5 –53.9 –54.1 –53.9 –54.2 –54.2 –54.2 160 KSYM/SEC 320 KSYM/SEC 640 KSYM/SEC 1280 KSYM/SEC –56.6 –55.1 –54.4 –54.3 –53.8 –55.9 –54.8 –54.1 –53.7 –53.5 Noise and DOCSIS At minimum gain, the AD8322’s output noise spectral density is 12 nV/ √Hz measured at 10 MHz. DOCSIS Table 4-8, “Spurious Emissions in 5 MHz to 42 MHz” specifies the output noise for various symbol rates. The calculated noise power in dBmV for 160 KSYM/SEC is: 20 12 160 60 46 4 2 log – . nV Hz kHz dBmV × += Comparing the computed noise power of –46.4 dBmV to the 8 dBmV signal yields –54.4 dBc, which meets the required level of –53 dBc set forth in DOCSIS Table 4-8. As the AD8322’s gain is increased from this minimum value, the output signal increases at a faster rate than the noise, resulting in a signal-to- noise ratio that improves with gain. In transmit disable mode the output noise spectral density computed over 160 KSYM/SEC is 1.0 nV/ √Hz or –68 dBmV. Evaluation Board Features and Operation The AD8322 evaluation board (Part # AD8322-EVAL) and control software can be used to control the AD8322 upstream cable driver via the parallel port of a PC. A standard printer cable connected between the parallel port and the evaluation board is used to feed all the necessary data to the AD8322 by means of the Windows ® based, Microsoft Visual Basic control software. This package provides a means of evaluating the amplifier by provid- ing a convenient way to program the gain/attenuation as well as offering easy control of the amplifiers asynchronous PD pin. With this evaluation kit the AD8322 can be evaluated with either a single-ended or differential input configuration. The amplifier can also be evaluated with or without the PULSE diplexer in the output signal path. To remove the diplexer from the signal path, move the two 0 Ω chip resistors R18 and R10 to locations R11 and R20. A schematic of the evaluation board is provided in Figure 13. Overshoot on PC Printer Ports The data lines on some PC parallel printer ports have excessive overshoot that may cause communications problems when pre- sented to the CLK pin of the AD8322 (TP5 on the evaluation board). The evaluation board was designed to accommodate a series resistor and shunt capacitor (R1 and C15) to filter the CLK signal if required. Transformer and Diplexer A 1:1 transformer is needed to couple the differential outputs of the AD8322 to the cable while maintaining a proper impedance match. The specified transformer is available from TOKO (Part # 617DB-A0070), however, MA/COM part # ETC-1-1T-15 can also be used. The evaluation board is equipped with the TOKO transformer, but is also designed to accept the MA/COM transformer. The PULSE diplexer included on the evaluation board provides a high-order low-pass filter function, typically used in the upstream path. The ability of the PULSE diplexer to achieve DOCSIS compliance is neither expressed nor implied by Analog Devices Inc. Data on the diplexer should be obtained from PULSE. Differential Inputs The AD8322-EVAL evaluation board is designed to accommo- date a Mini-Circuits T1-6T-KK81 1:1 transformer for the purpose of converting a single-ended (ground referenced) input signal to differential inputs. Figure 8 and the following paragraphs iden- tify three options for providing differential input signals to the AD8322 evaluation board. Windows is a registered trademark of Microsoft Corporation. |
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