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AD9040A Arkusz danych(PDF) 9 Page - Analog Devices |
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AD9040A Arkusz danych(HTML) 9 Page - Analog Devices |
9 / 16 page REV. D AD9040A –9– Some applications may require greater accuracy, improved temperature performance, or adjustment of the gain (input range) of the AD9040A, which cannot be obtained by using the internal reference. For these applications, an external 2.5 V reference can be used, as shown in Figure 4. The VREF input requires 5 µA of drive current. REF AMP BAND GAP REFERENCE REFERENCE AD9040A VOUT VREF –VS BPREF REFERENCE 0.1 F 0.1 F Figure 4. Using External Reference In applications using multiple AD9040As, slaving the reference inputs to a single reference output will improve gain tracking among the ADCs, as shown in Figure 5. VOUT VREF AD9040A –VS –VS –VS VREF AD9040A VREF 0.1 F 0.1 F 0.1 F 0.1 F 0.1 F 0.1 F AD9040A BPREF BPREF BPREF Figure 5. Slaving Multiple AD9040As to a Single Internal Reference In the Specifications table, the gain temperature coefficient parameter under dc accuracy applies to the ADC when the inter- nal reference is being used. If an external reference is used, its temperature coefficient must be taken into account to deter- mine overall temperature performance. The input range can be varied by adjusting the reference voltage applied to the AD9040A. By decreasing the reference voltage, the gain can be reduced approximately 10% with no degrada- tion in performance. Increasing the reference voltage increases the gain, but for proper operation, the reference voltage should not exceed 2.6 V. Time-Gain Control ADC Ultrasound and sonar systems require an increase in gain versus time. This allows the system to correct for attenuation of return pulses. Figure 6 shows the AD600/AD602 amplifier and the AD9040A ADC configured as a time-gain control analog-to- digital converter. The control voltage ramps from –625 mV to +625 mV, permitting 40 dB of gain-control range. The voltage used for gain control can be either a linear ramp or the output of a voltage-output DAC, such as the AD7242. –625mV +625mV GAIN CONTROL VOLTAGE AD600/AD602 A1H1 AD9040A Figure 6. Ultrasound/Sonar Time-Gain Control ADC using X-AMP™ Transient Response Figure 7 illustrates the method for evaluating ADC transient performance. Two synthesizers are locked in synchronization but tuned to frequencies that are slightly offset from a 2 to 1 submultiple. One synthesizer clocks a flat pulse network at a frequency of 19.9609375 MHz to provide the analog input signal; the other synthesizer output is shaped to provide a CMOS 40 MHz sam- pling clock. At the output of the AD9040A, output data reflects an interleaved alias of the input pulse. The repetitive sampling allows the measurement of ADC transient response as shown in the TPCs in this data sheet. AD9040A MARCONI 2030 SYNTHESIZER REF MARCONI 2030 SYNTHESIZER REF 19.9609375MHz 40MHz FLAT PULSE NETWORK SINE TO CMOS ANALOG IN ENCODE OUTPUT Figure 7. Transient Response Test |
Podobny numer części - AD9040A_15 |
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Podobny opis - AD9040A_15 |
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