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AD9050 Datasheet(PDF) 9 Page - Analog Devices |
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AD9050 Datasheet(HTML) 9 Page - Analog Devices |
9 / 12 page ![]() AD9050 –9– REV. B Overdrive of the Analog Input Special care was taken in the design of the analog input section of the AD9050 to prevent damage and corruption of data when the input is overdriven. The nominal input range is +2.788 V to 3.812 V (1.024 V p-p centered at 3.3 V). Out-of-range com- parators detect when the analog input signal is out of this range and shut the T/H off. The digital outputs are locked at their maximum or minimum value (i.e., all “0” or all “1”). This pre- cludes the digital outputs from changing to an invalid value when the analog input is out of range. When the analog input signal returns to the nominal range, the out-of-range comparators switch the T/H back to the active mode and the device recovers in approximately 10 ns. The input is protected to one volt outside the power supply rails. For nominal power (+5 V and ground), the analog input will not be damaged with signals from +6.0 V to –1.0 V. Timing The performance of the AD9050 is very insensitive to the duty cycle of the clock. Pulse width variations of as much as ±10% will cause no degradation in performance. (see Figure 13, SNR vs. Clock Pulse Width). The AD9050 provides latched data outputs, with five pipeline delays. Data outputs are available one propagation delay (tPD) after the rising edge of the encode command (refer to the AD9050 Timing Diagram). The length of the output data lines and loads placed on them should be minimized to reduce tran- sients within the AD9050; these transients can detract from the converter’s dynamic performance. The minimum guaranteed conversion rate of the AD9050 is 3 MSPS. Below a nominal of 1.5 MSPS the internal T/H switches to a track function only. This precludes the T/H from drooping to the rail during the conversion process and mini- mizes saturation issues. At clock rates below 3 MSPS dynamic performance degrades. The AD9050 will operate in burst mode operation, but the user must flush the internal pipeline each time the clock stops. This requires five clock pulses each time the clock is restarted for the first valid data output (refer to Fig- ure 2 Timing Diagram). Power Dissipation The power dissipation specification in the parameter table is measured under the following conditions: encode is 40 MSPS or 60 MSPS, analog input is –0.5 dBFS at 10.3 MHz, the digi- tal outputs are loaded with approximately 7 pF (10 pF maxi- mum) and VDD is 5 V. These conditions intend to reflect actual usage of the device. As shown in Figure 4, the actual power dissipation varies based on these conditions. For instance, reducing the clock rate will reduce power as expected for CMOS-type devices. Also the loading determines the power dissipated in the output stages. From an ac standpoint, the capacitive loading will be the key (refer to Equivalent Output Stage). The analog input frequency and amplitude in conjunction with the clock rate determine the switching rate of the output data bits. Power dissipation increases as more data bits switch at faster rates. For instance, if the input is a dc signal that is out of range, no output bits will switch. This minimizes power in the output stages, but is not realistic from a usage standpoint. The dissipation in the output stages can be minimized by inter- facing the outputs to 3 V logic (refer to USING THE AD9050, 3 V System). The lower output swings minimize consumption. Refer to Figure 4 for performance characteristics. Voltage Reference A stable and accurate +2.5 V voltage reference is built into the AD9050 (Pin 3, VREF Output). In normal operation the internal reference is used by strapping Pins 3 and 4 of the AD9050 to- gether. The internal reference has 500 µA of extra drive current that can be used for other circuits. Some applications may require greater accuracy, improved tem- perature performance, or adjustment of the gain of the AD9050, which cannot be obtained by using the internal reference. For these applications, an external +2.5 V reference can be used to connect to Pin 4 of the AD9050. The VREFIN requires 5 µA of drive current. The input range can be adjusted by varying the reference volt- age applied to the AD9050. No appreciable degradation in per- formance occurs when the reference is adjusted ±5%. The full-scale range of the ADC tracks reference voltage changes linearly. |
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