Datenblatt-Suchmaschine für elektronische Bauteile |
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AD648A Datenblatt(PDF) 7 Page - Analog Devices |
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AD648A Datenblatt(HTML) 7 Page - Analog Devices |
7 / 12 page AD648 REV. C –7– SIGN BIT BINARY NUMBER IN DAC REGISTER ANALOG OUTPUT 0 1111 1111 1111 +VIN (4095/4096) 0 0000 0000 0000 0 VOLTS 1 0000 0000 0000 0 VOLTS 1 1111 1111 1111 –VIN (4095/4096) NOTE: SIGN BIT AT "0" CONNECTS THE NONINVERTING INPUT OF A2 TO ANALOG COMMON Figure 25. Sign Magnitude Code Table Figure 23c shows a diode clamp protection scheme for an I-to-V converter using low leakage diodes. Because the diodes are con- nected to the op amp’s summing junction, which is a virtual ground, their leakage contribution is minimal. Figure 23c. I-to-V Converter with Diode Input Protection Exceeding the negative common-mode range on either input terminal causes a phase reversal at the output, forcing the ampli- fier output to the corresponding high or low state. Exceeding the negative common mode on both inputs simultaneously forces the output high. Exceeding the positive common-mode range on a single input doesn’t cause a phase reversal; but if both inputs exceed the limit, the output will be forced high. In all cases, normal amplifier operation is resumed when input voltages are brought back within the common-mode range. D/A CONVERTER BIPOLAR OUTPUT BUFFER The circuit in Figure 24 provides 4 quadrant multiplication with a resolution of 12 bits. The AD648 is used to convert the AD7545 CMOS DAC’s output current to a voltage and provides the necessary level shifting to achieve a bipolar voltage output. The circuit operates with a 12-bit plus sign input code. The transfer function is shown in Figure 25. The AD7592 is a fully protected dual CMOS SPDT switch with data latches. R4 and R5 should match to within 0.01% to main- tain the accuracy of the converter. A mismatch between R4 and R5 introduces a gain error. Overall gain is trimmed by adjusting RIN. The AD648’s low input offset voltage, low drift over tem- perature, and excellent dynamics make it an attractive low power output buffer. The input offset voltage of the AD648 output amplifier results in an output error voltage. This error voltage equals the input offset voltage of the op amp times the noise gain of the amplifier. That is: VOS Output = VOS Input 1 + RFB RO RFB is the feedback resistor for the op amp, which is internal to the DAC. RO is the DAC’s R-2R ladder output resistance. The value of RO is code dependent. This has the effect of changing the offset error voltage at the amplifier’s output. An output am- plifier with a sub millivolt input offset voltage is needed to pre- serve the linearity of the DAC’s transfer function. Figure 24. 12-Bit Plus Sign Magnitude D/A Converter |
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Ähnliche Beschreibung - AD648A |
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