Datasheet AD9731 (Analog Devices) - 10

AD9731
The REFERENCE IN pin can also be driven directly for wider An operational amplifier can also be used to perform the I-to-V bandwidth multiplying operation. The analog signal for this mode conversion of the DAC output. Figure 5 shows an example of a of operation must have a signal swing in the range of –3.3 V to circuit that uses the AD9631, a high speed, current feedback –4.25 V. This can be implemented by capacitively coupling into amplifier. The resistor values in Figure 5 provide a 4.096 V REFERENCE IN a signal with a dc bias of –3.3 V (IOUT ª swing, centered at ground, at the output of the AD9631 amplifier. 22.5 mA) to –4.25 V (IOUT ª 3 mA), as shown in Figure 4, or by dividing REFERENCE IN with a low impedance op amp whose
10k
⍀ signal swing is limited to the stated range.
1/2 10k
⍀ NOTE: When using an external reference, the external refer-
AD708 1/2 I
ence voltage must be applied prior to applying –V
FS
S.
AD708 R1 200
⍀
R2 100
⍀
AD9731 RFB REF CONTROL RFF 400
⍀
OUT AMP IN IFS 25
⍀
APPROX –3.8V IOUT 2048V RL AD9631 V 25
⍀
OUT AD9731 OBSOLETE REFERENCE IN –VS IOUTB –VS 25
⍀ Figure 5. I-to-V Conversion Using a Current Feedback Figure 4. Wideband Multiplying Circuit Amplifier
Analog Output
The switch network provides complementary current outputs
EVALUATION BOARD
IOUT and IOUTB. The design of the AD9731 is based on statisti- The performance characteristics of the AD9731 make it ideally cal current source matching, which provides a 10-bit linearity suited for direct digital synthesis (DDS) and other waveform without trim. Current is steered to either IOUT or IOUTB in pro- synthesis applications. The AD9731 evaluation board provides a portion to the digital input word. The sum of the two currents is platform for analyzing performance under optimum layout con- always equal to the full-scale output current minus 1 LSB. The ditions. The AD9731 also provides a reference for high speed current can be converted to a voltage by resistive loading as circuit board layout techniques. shown in the block diagram. Both IOUT and IOUTB should be equally loaded for best overall performance. The voltage that is developed is the product of the output current and the value of the load resistor. –10– REV. B Document Outline FEATURES APPLICATIONS FUNCTIONAL BLOCK DIAGRAM GENERAL DESCRIPTION SPECIFICATIONS ABSOLUTE MAXIMUM RATINGS EXPLANATION OF TEST LEVELS ORDERING GUIDE PIN FUNCTION DESCRIPTIONS PIN CONFIGURATION Typical Performance Characteristics THEORY AND APPLICATIONS Digital Inputs/Timing Input Clock and Data Timing Relationship References Analog Output EVALUATION BOARD OUTLINE DIMENSIONS Revision History