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Datenblatt-Suchmaschine für elektronische Bauteile |
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Datenblatt-Suchmaschine für elektronische Bauteile |
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AD9226AST Datenblatt(PDF) 15 Page - Analog Devices |
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AD9226AST Datenblatt(HTML) 15 Page - Analog Devices |
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15 / 28 page  REV. B AD9226 –15– 10 F VINA VREF AD9226 VINB 0.5V SENSE REFCOM 0.1 F 10 F 0.1 F 0.1 F 15pF 1.5V 33 33 1V 0.1 F CAPT CAPB Figure 5a. 1 V Single-Ended Input, Common-Mode Voltage = 1 V 10 F VINA VREF AD9226 VINB 0.75V SENSE 0.1 F 10 F 0.1 F 0.1 F 15pF 1.25V 33 33 1V 0.1 F 49.9 1.25V 0.75V CAPB CAPT Figure 5b. 1 V Differential Input, Common-Mode Voltage = 1 V 10 F VINA VREF AD9226 VINB 1.5V SENSE 0.1 F 10 F 0.1 F 0.1 F 15pF 2.5V 33 33 2V 0.1 F 49.9 2.5V 1.5V CAPT CAPB Figure 5c. 2 V Differential Input, Common-Mode Voltage = 2 V 10 F VINA VREF AD9226 VINB 1.0V SENSE REFCOM 0.1 F 10 F 0.1 F 0.1 F 15pF 3.0V 33 33 2V 0.1 F CAPT CAPB Figure 5d. 2 V Single-Ended Input, Common-Mode Voltage = 2 V 10 F VINA VREF AD9226 (LQFP) VINB 2.0V SENSE 0.1 F 10 F 0.1 F 0.1 F 15pF 3.0V 33 33 2V 0.1 F 49.9 3.0V 2.0V 2.5V 2.5V CMLEVEL 0.1 F 2.5V CAPB CAPT Figure 5e. 2 V Differential Input, Common-Mode Voltage = 2.5 V 10 F VINA VREF AD9226 VINB 2.0V SENSE 0.1 F 10 F 0.1 F 0.1 F 15pF 2.75V 33 33 1V 0.1 F 49.9 2.75V 2.25V 2.5V 2.5V CAPT CAPB 0.1 F 2.5V AVDD 10k 10k Figure 5f. 1 V Differential Input, Common-Mode Voltage = 2.5 V (Recommended for IF Undersampling) The differential input characterization for this data sheet was performed using the configuration shown in Figure 7. Since not all applications have a signal preconditioned for differential operation, there is often a need to perform a single- ended-to-differential conversion. In systems that do not need to be dc-coupled, an RF transformer with a center tap is the best method to generate differential inputs for the AD9226. It pro- vides all the benefits of operating the ADC in the differential mode without contributing additional noise or distortion. An RF transformer also has the added benefit of providing electrical isolation between the signal source and the ADC. An improvement in THD and SFDR performance can be realized by operating the AD9226 in the differential mode. The performance enhance- ment between the differential and single-ended mode is most noteworthy as the input frequency approaches and goes beyond the Nyquist frequency (i.e., fIN > FS /2). The circuit shown in Figure 6a is an ideal method of applying a differential dc drive to the AD9226. It uses an AD8138 to derive a differential signal from a single-ended one. Figure 6b illustrates its performance. Figure 7 presents the schematic of the suggested transformer circuit. The circuit uses a Minicircuits RF transformer, model T1-1T, which has an impedance ratio of four (turns ratio of 2). The schematic assumes that the signal source has a 50 Ω source impedance. The center tap of the transformer provides a con- venient means of level-shifting the input signal to a desired common-mode voltage. In Figure 7 the transformer centertap is connected to a resistor divider at the midsupply voltage. |
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