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AD10265 Datenblatt(PDF) 11 Page - Analog Devices |
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AD10265 Datenblatt(HTML) 11 Page - Analog Devices |
11 / 18 page AD10265 –11– REV. 0 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 AD10265 ECL GATE 0.1 F 0.1 F –VS 510 510 Figure 19. 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 AD10265 0.1 F 0.1 F –VS 50 AD96687 (1/2) 510 510 Figure 20. ECL Comparator for Encode USING THE FLEXIBLE INPUT The AD10265 has been designed with the user’s ease of opera- tion in mind. Multiple input configurations have been included on board to allow the user a choice of input signal levels and input impedance. While the standard inputs are ±0.5 V, ±1.0 V and ±2.0 V, the user can select the input impedance of the AD10265 on any input by using the other inputs as alternate locations for GND or an external resistor. The following chart summarizes the impedance options available at each input location: AIN1 = 100 Ω when AIN2 and AIN3 Are Open. AIN1 = 75 Ω when A IN3 Is Shorted to GND. AIN1 = 50 Ω when A IN2 Is Shorted to GND. AIN2 = 200 Ω when AIN3 Is Open. AIN2 = 100 Ω when A IN3 Is Shorted to GND. AIN2 = 75 Ω when A IN2 to AIN3 Has an External Resistor of AIN2 = 300 Ω, with AIN 3 Shorted to GND. AIN2 = 50 Ω when A IN2 to AIN3 Has an External Resistor of AIN2 = 100 Ω, with A IN3 Shorted to GND. AIN3 = 400 Ω. AIN3 = 100 Ω when A IN3 Has an External Resistor of 133 Ω to GND. AIN3 = 75 Ω when A IN3 Has an External Resistor of 92 Ω to GND. AIN3 = 50 Ω when AIN3 Has an External Resistor of 57 Ω to GND. GROUNDING AND DECOUPLING Analog and Digital Grounding Proper grounding is essential in any high speed, high resolution system. Multilayer printed circuit boards (PCBs) are recom- mended to provide optimal grounding and power schemes. The use of ground and power planes offers distinct advantages: 1. The minimization of the loop area encompassed by a signal and its return path. 2. The minimization of the impedance associated with ground and power paths. 3. The inherent distributed capacitor formed by the power plane, PCB insulation and ground plane. These characteristics result in both a reduction of electro- magnetic interference (EMI) and an overall improvement in performance. It is important to design a layout that prevents noise from cou- pling to the input signal. Digital signals should not be run in parallel with input signal traces and should be routed away from the input circuitry. The AD10265 does not distinguish between analog and digital ground pins as the AD10265 should always be treated as an analog component. All ground pins should be connected together directly under the AD10265. The PCB should have a ground plane covering all unused portions of the component side of the board to provide a low impedance path and manage the power and ground currents. The ground plane should be removed from the area near the input pins to reduce stray capacitance. LAYOUT INFORMATION The schematic of the evaluation board (Figure 21) represents a typical implementation of the AD10265. The pinout of the AD10265 is very straightforward and facilitates ease of use and the implementation of high frequency/high resolution design practices. It is recommended that high quality ceramic chip capacitors be used to decouple each supply pin to ground directly at the device. All capacitors can be standard high quality ceramic chip capacitors. Care should be taken when placing the digital output runs. Because the digital outputs have such a high slew rate, the capacitive loading on the digital outputs should be minimized. Circuit traces for the digital outputs should be kept short and connect directly to the receiving gate. Internal circuitry buffers the outputs of the AD6640 ADC through a resistor network to eliminate the need to externally isolate the device from the receiving gate. |
Ähnliche Teilenummer - AD10265 |
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Ähnliche Beschreibung - AD10265 |
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