Ultrahigh Speed Converter AD9768 Analog Devices AD9768SD converte

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Ultrahigh Speed Converter AD9768 Analog Devices AD9768SD converte

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FEATURES Settling Time MSPS Update Rate Output Current ECL-Compatible Multiplying Mode APPLICATIONS Raster Scan Vector Graphic Displays High Speed Waveform Generation Digital VCOs Ultrafast Digital Attenuators GENERAL DESCRIPTION
Ultrahigh Speed Converter AD9768
Analog Devices AD9768SD converter monolithic current-output converter which accept bits ECL-level digital input voltages convert them into analog signals update rates high MSPS. addition standard converter, also utilized two-quadrant multiplying multiplying bandwidths high MHz. inherently glitch design used, complementary current outputs suitable driving transmission lines directly. Nominal full-scale output which corresponds volt drop across load, volt across returned volt. actual output current determined on-chip reference voltage (VREF -1.26 external current setting resistor, RSET. Full-scale output current IOUT with digital inputs calculated with equation:
reference voltage source modified bandgap type nominally -1.26 volts. This reference supply requires external regulation. reduce possibility noise generation and/or instability, (REFERENCE OUT) decoupled using high-quality ceramic chip capacitor. Stabilization internal loop amplifier single capacitor connected from (COMPENSATION) ground. minimum value this capacitor 3900 although 0.01 ceramic chip capacitor recommended. incredible speed characteristics AD9768SD converter make attractive wide range high speed applications. ability unit operate twoquadrant multiplying converter adds another dimension usefulness makes AD9768SD truly versatile device.
AD9768SE CONNECTIONS
IOUT
VRET -VREF RSET
setting resistor RSET output load resistor should both have temperature coefficients. complementary IOUT also provided.
AD9768JD/SD CONNECTIONS
REV.
Information furnished Analog Devices believed accurate reliable. However, responsibility assumed Analog Devices use, infringements patents other rights third parties which result from use. license granted implication otherwise under patent patent rights Analog Devices.
Technology Way, P.O. 9106, Norwood, 02062-9106, U.S.A. Tel: 617/329-4700 Fax: 617/326-8703
AD9768-SPECIFICATIONS (typical under following conditions unless otherwise noted;=nominal digital input levels; nominal power supplies;
Parameter RESOLUTION(FS FULL SCALE) WEIGHT (CURRENT) ACCURACY1 Differential Nonlinearity Integral Nonlinearity Monotonicity Zero Offset (lnitial) TEMPERATURE COEFFICIENTS Zero Offset Reference Voltage (-1.26 DIGITAL DATA INPUTS Logic Compatibility Logic Voltage Levels Coding OUTPUT Current (Unipolar) IOUT Digital Input Digital Input IOUT(@ Digital Input Digital Input Compliance Impedance SPEED PERFORMANCE Settling Time 0.2% FS)2 Slew Rate Update Rate Rise Time Glitch Energy REFERENCE Internal, Monolithic3 External, Variable4 Voltage-Multiplying Mode Current-Multiplying Mode
Unit Bits ppm/°C ppm/°C
AD9768SJD/SD/SE Guaranteed
Parameter CURRENT-MULTIPLYING MODE (See Figure Range Pins Resistance Transfer Function
Unit
AD9768SJD/SD/SE
-0.9 -1.7 Binary (BIN) Unipolar Offset Binary (OBN) Bipolar (max) (Pin (Pin 15%) V/µs MSPS pV-sec (max) (max) (30) -0.7 +3.0 -1.1 +3.0 -1.26 -1.1 (-2) (-7.5
Large Signal Bandwidth (-3dB Point) POWER REQUIREMENTS -5.2 0.25 +5.0 0.25 Power Dissipation Power Supply Sensitivity5 TEMPERATURE RANGES6 Operating AD9768JD AD9768SD/SE Storage THERMAL RESlSTANCE Junction Air, (Free Air) Junction Case, PACKAGE OPTION8 Ceramic (D-18) (E-20A)
Measured Digital Applied Bits 1-8: Input IOUT Input IOUT Measured Digital Applied Bits 1-8: Input IOUT Input IOUT (max) (max) (max) 66(70) 14(15) 410(430) 0.07
°C/W °C/W AD9768JD AD9768SD AD9768SE
+125 +150
VOLTAGE-MULTIPLYING MODE (See Figure Range Center -0.6 Resistance Transfer Function Measured Digital Applied Bits 1-8: -0.1 Input IOUT -1.1 Input IOUT Measured Digital Applied Bits 1-8: -0.1 Input IOUT -1.1 Input IOUT Large Signal Bandwidth Point)
NOTES Relative including linearity (within voltage compliance limits). Worst case settling time; includes Most Significant (MSB) transitions. Applies when operating AD9768 standard D/A. Based ohms; RSET ohms; change either power supply voltage causes 0.07% change analog output. Case temperature. Maximum junction temperature 125°C. Ceramic DIP, Leadless Ceramic Chip Carrier. Specifications subject change without notice.
AD9768SD Schematic
REV.
AD9768
THEORY OPERATION
Refer AD9768SD schematic. transistors pictured bottom diagram, connected paired transistors middle schematic, current sources which always "on". paired transistors differential current switches, designed steer current from current sources either (IO) Digital inputs applied Pins determine which transistors will operating each pair establish what current will flow Pins transistor extreme left schematic base reference paired current switches used assure switches will centered around voltage swing. diodes connected base this transistor temperature compensation devices base reference circuit. There three different current sources AD9768 D/A. eight transistors shown bottom schematic structured identical groups four current sources, each which binarily weighted. group, comprised four right, connected group through 15:1 current divider made resistor networks. geometry AD9768 guarantees binary weighing ratios among 100, 200, resistors each emitter circuit correct. resistor values which shown indicate ratios among resistors, their nominal values. third current source single transistor, pictured lower left portion schematic with collector connected RSET. function help establish base voltage eight current sources; works conjunction with external RSET resistor selected user AD9768, reference amplifier. Current flowing through this transistor referred figures text. When AD9768 operating conventional current-output converter, develops voltage across RSET which inputs on-board reference amplifier shown schematic. other input this amplifier on-chip reference voltage -1.26 volts. output reference amplifier adjusts current-source base reference voltage this, turn, adjusts value single-transistor current source causes develop voltage across RSET which maintains -1.26 volts on-chip reference supply. maintain good stability internal loop reference amplifier, ceramic chip capacitor with nominal value 0.01 should connected COMPENSATION; minimum recommended value this capacitor 3900 temperature coefficient load resistor (RL) affect performance AD9768 converter, with current-output converter. design AD9768 dependence external RSET resistor, however, make sensitive also tempco RSET. user cautioned select RSET resistors which have temperature coefficients. DIGITAL GROUND (Pin ANALOG RETURN (Pin normally connected together; this connection should made close possible device case minimize possible noise problems. AD9768 similar other highREV.
speed, high performance device: optimum requires careful attention design details, including layout circuit which converter used.
CONVENTIONAL AD9768SD
Refer Figure Conventional AD9768SD. output current AD9768 appears (IO) develops voltage across load resistor which based (the current flowing through single-transistor source discussed above) Value
Figure Conventional AD9768SD
function return voltage (VRET), reference voltage (VREF), value RSET; these selected user application. necessary equations calculating precise values each part Figure indicated, voltage drop across added return voltage; resulting voltage total VOUT converter.
VOLTAGE MULTIPLYING MODE
addition ultra-high speed current output converter, AD9768 also used two-quadrant multiplying either voltage mode current mode. Refer Figure Multiplying AD9768 (Voltage Mode). When operating this mode, analog output AD9768 influenced digital inputs external multiplying voltage (VM) applied REFERENCE which takes place internal reference used when operating conventional manner.
Figure Multiplying AD9768 (Voltage Mode)
value flowing through RSET voltage VRET minus multiplying voltage (VM), divided RSET; amount this current part equation which establishes analog output (VOUT) AD9768 chosen user application. when operating conventional fashion, VRET value between volts volts. (for purposes discussion here) some negative voltage varied over range which approximately volt peak-to-peak.
AD9768
load resistor (RL) value ohms, RSET value ohms, VRET center voltage will -0.6 vary from -0.1 -1.1 Typically, frequency these variations upper limit when operating voltage multiplying mode; that frequency point bandwidth internal reference amplifier. combined effects variations changes digital input values shown Figure IOUT Multiplying Voltage. this illustration, ordinate graph expressed terms milliamps IOUT current VOUT, course, will function value chosen user. some voltage chosen user particular application; value this voltage based part size load resistor range have frequency components high MHz. VADJ RADJ provide offset adjustment compensate component assure always unipolar current between values required voltages resistors calculated using equations which part Figure Refer Figure IOUT Multiplying Current.
Figure IOUT Multiplying Current
Figure IOUT Multiplying Voltage
negative value horizontal axis shown starting approximately -0.1 rather than because AD9768 must have some small value voltage applied perform multiplying function. conditions shown figure, output current starts become nonlinear approximately because maximum output drive capabilities device. Different values RSET would alter point where limiting first appears.
CURRENT MULTIPLYING MODE
shown, vary over range value approximately practical lower limit because nonlinearities extremely small current levels. These changes combined with variations digital inputs, producing complex changes output current VOUT. "rounding" current curve graph result IOUT approaching maximum drive capabilities AD9768 needs taken into account assure optimum performance selected application.
OUTLINE DIMENSIONS
Dimensions shown inches (mm).
AD9768 converter operated markedly higher multiplying rates when operated current-multiplying mode, contrasted with voltage multiplying mode. Refer Figure Multiplying AD9768SD (Current Mode).
Ceramic (D-18)
(E-20A)
Figure Multiplying AD9768SD (Current Mode)
this mode, internal reference amplifier inherent frequency limitations replaced current source comprised associated circuits. These circuits supply unipolar current which one-fourth full-scale output current (with digital applied inputs) current flow through load resistor. REV.
PRINTED U.S.A.
C753c-5-12/89

Ultrahigh Speed Converter AD9768 Analog Devices AD9768SD converte

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