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AD10242 bảng dữ liệu(PDF) 11 Page - Analog Devices |
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AD10242 bảng dữ liệu(HTML) 11 Page - Analog Devices |
11 / 16 page AD10242 –11– REV. A If a logic threshold other than the nominal 1.6 V is required, the following equations show how to use an external resistor, RX, to raise or lower the trip point (see Figure 4, R1 = 17 k Ω, R2 = 8 k Ω). V1 = 5R2RX R1R2 + R1R X + R2RX to lower logic threshold. 0.01µF ENCODE SOURCE ENCODE ENCODE AD10242 RX Vl +5V R1 R2 Figure 21. Lower Threshold for Encode V1 = 5R2 R2 + R1RX R1 + R X to raise logic threshold. 0.01µF ENCODE SOURCE ENCODE ENCODE AD10242 RX Vl +5V R1 R2 AVCC Figure 22. Raise Logic Threshold for Encode While the single ended encode will work well for many applica- tions, driving the encode differentially will provide increased performance. Depending on circuit layout and system noise, a 1 dB to 3 dB improvement in SNR can be realized. It is recom- mended that the encode signal be ac-coupled into the ENCODE and ENCODE pins. The simplest option is shown below. The low jitter TTL signal is coupled with a limiting resistor, typically 100 Ω, to the pri- mary side of an RF transformer (these transformers are inexpen- sive and readily available; Part No. in figure is from Mini- Circuits). The secondary side is connected to the ENCODE and ENCODE pins of the converter. Since both encode inputs are self-biased, no additional components are required. TTL ENCODE ENCODE AD10242 100 Ω T1-1T Figure 23. TTL Source—Differential Encode If no TTL source is available, a clean sine wave may be substi- tuted. In the case of the sine source, the matching network is shown below. Since the matching transformer specified is a 1:1 impedance ratio, R, the load resistor should be selected to match the source impedance. The input impedance of the AD9042 is negligible in most cases. ENCODE ENCODE AD10242 R T1-1T SINE SOURCE Figure 24. Sine Source—Differential Encode If a low jitter ECL clock is available, another option is to ac- couple a differential ECL signal to the encode input pins as shown below. The capacitors shown here should be chip capaci- tors but do not need to be of the low inductance variety. ENCODE ENCODE AD10242 ECL GATE 0.1µF 0.1µF –VS 510 Ω 510 Ω Figure 25. Differential ECL for Encode As a final alternative, the ECL gate may be replaced by an ECL comparator. The input to the comparator could then be a logic signal or a sine signal. ENCODE ENCODE AD10242 0.1µF 0.1µF –VS 50 Ω AD96687 (1/2) 510 Ω 510 Ω Figure 26. ECL Comparator for Encode Care should be taken not to overdrive the encode input pin when ac coupled. Although the input circuitry is electrically pro- tected from over or under voltage conditions, improper circuit operations may result from overdriving the encode input pin. |
Số phần tương tự - AD10242 |
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Mô tả tương tự - AD10242 |
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