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AD768-EB Fiches technique(PDF) 5 Page - Analog Devices |
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AD768-EB Fiches technique(HTML) 5 Page - Analog Devices |
5 / 20 page AD768 REV. B –5– Temperature Drift Temperature drift is specified as the maximum change from the ambient (+25 °C) value to the value at either T MIN or TMAX. For offset and gain drift, the drift is reported in ppm of full-scale range (FSR) per degree C. For reference drift, the drift is re- ported in ppm per degree C. Power Supply Rejection The maximum change in the full-scale output as the supplies are varied from nominal to minimum and maximum specified voltages. Settling Time The time required for the output to reach and remain within a specified error band about its final value, measured from the start of the output transition. Spurious-Free Dynamic Range The difference, in dB, between the rms amplitude of the input signal and the peak spurious signal over the specified bandwidth. Total Harmonic Distortion THD is the ratio of the rms sum of the first six harmonic com- ponents to the rms value of the measured input signal. It is ex- pressed as a percentage or in decibels (dB). Glitch Impulse Asymmetrical switching times in a DAC give rise to undesired output transients which are quantified by a glitch impulse. It is specified as the net area of the glitch in pV-sec. DEFINITIONS OF SPECIFICATIONS Linearity Error (Also Called Integral Nonlinearity or INL) Linearity error is defined as the maximum deviation of the ac- tual analog output from the ideal output, determined by a straight line drawn from zero to full scale. Differential Nonlinearity (or DNL) DNL is the measure of the variation in analog value, normalized to full scale, associated with a 1 LSB change in digital input code. Monotonicity A D/A converter is monotonic if the output either increases or remains constant as the digital input increases. Offset Error The deviation of the output current from the ideal of zero is called offset error. For IOUTA, 0 mA output is expected when the inputs are all 0s. For IOUTB, 0 mA output is expected when all inputs are set to 1s. Gain Error The difference between the actual and ideal output span. The actual span is determined by the output when all inputs are set to 1s minus the output when all inputs are set to 0s. The ideal output current span is 4 × the current applied to the IREFIN pin. Output Compliance Range The range of allowable voltage at the output of a current-output DAC. Operation beyond the maximum compliance limits may cause either output stage saturation or breakdown, resulting in nonlinear performance. 5mA 6 CREFCOMP 1µF RREF 500 Ω REFIN REFOUT NC VDD 3 4 +2.5V REF 25 5 REFCOM 1µF CNR 2 NR VEE 26 15 1µF 1µF +5V –5V DCOM RLAD 1k Ω RLAD 1k Ω IOUTA IOUTB LADCOM 1 28 27 50 Ω RLOAD 50 Ω IOUTA IOUTB SEGMENTED CURRENT SOURCES CURRENT SOURCES AND R-2R LADDER CLOCK 21 22 23 24 19 20 13 14 17 18 7 8 9 10 11 12 LATCHES – LOWER 12 BITS 16 MSB DECODE & LATCHES CLOCK AD768 Figure 1. Functional Block Diagram and Basic Hookup FUNCTIONAL DESCRIPTION The AD768 is a current-output DAC with a nominal full-scale current of 20 mA and a 1 k Ω output impedance. Differential outputs are provided to support single-ended or differential applications. The DAC architecture combines segmented cur- rent sources for the top four bits (MSBs) and a 1 k Ω R-2R lad- der for the lower 12 bits (LSBs). The DAC current sources are implemented with laser-trimmable thin film resistors for excel- lent dc linearity. A proprietary switching technique is utilized to reduce glitch energy and maximize dynamic accuracy. The digital interface offers CMOS compatible edge-triggered input latches that interface readily to CMOS logic and supports clock rates up to 40 MSPS. A temperature compensated 2.5 V bandgap reference is integrated on-chip to drive the AD768 ref- erence input current with the use of a single external resistor. The functional block diagram in Figure 1 is a simple representa- tion of the internal circuitry to aid the understanding of the AD768’s operation. The DAC transfer function is described, and followed by a detailed description of each key portion of the circuit. Typical circuit configurations are shown in the section APPLYING THE AD768. |
Numéro de pièce similaire - AD768-EB |
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Description similaire - AD768-EB |
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