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AD7228KN データシート(PDF) 11 Page - Analog Devices |
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AD7228KN データシート(HTML) 11 Page - Analog Devices |
11 / 16 page AD7228 Data Sheet Rev. D | Page 10 of 15 Table 7. Unipolar Code Table DAC Latch Contents MSB LSB1 Analog Output 1 1 1 1 1 1 1 1 +VREF(255/256) 1 0 0 0 0 0 0 1 +VREF(129/256) 1 0 0 0 0 0 0 0 +VREF 2 256 128 REF V + = 0 1 1 1 1 1 1 1 +VREF(127/256) 0 0 0 0 0 0 0 1 +VREF(1/256) 0 0 0 0 0 0 0 0 0 V 1 1 LSB = (VREF)(2−8) = VREF (1/256). Bipolar Output Operation Each of the DACs on the AD7228 can be individually configured for bipolar output operation. This is possible using one external amplifier and two resistors per channel. Figure 11 shows a circuit used to implement offset binary coding (bipolar operation) with DAC 1 of the AD7228. In this case, ) ( ) ( 1 1 REF REF OUT V R1 R2 V D R1 R2 V × − × × + = With R1 = R2, VOUT = (2D1 − 1) × (VREF) where D1 is a fractional representation of the digital word in Latch 1 of the AD7228 (0 ≤ D1 ≤ 255/256). Table 8. Bipolar Code Table DAC Latch Contents MSB LSB Analog Output 1 1 1 1 1 1 1 1 +VREF(127/128) 1 0 0 0 0 0 0 1 +VREF(1/128) 1 0 0 0 0 0 0 0 0 V 0 1 1 1 1 1 1 1 −VREF(1/128) 0 0 0 0 0 0 0 1 −VREF(127/128) 0 0 0 0 0 0 0 0 −VREF(128/128) = −VREF Mismatch between R1 and R2 causes gain and offset errors; therefore, these resistors must match and track over temperature. The AD7228 can be operated from a single supply or from dual supplies. Table 8 shows the digital code vs. output voltage relationship for the circuit of Figure 11 with R1 = R2. AC Reference Signal In some applications, it may be desirable to have an ac signal applied as the reference input to the AD7228. The AD7228 has multiplying capability within the upper (10 V) and lower (2 V) limits of reference voltage when operated with dual supplies. Therefore, ac signals must be ac-coupled and biased up before being applied to the reference input. Figure 12 shows an ac signal applied to the reference input of the AD7228. For input frequencies up to 50 kHz, the output distortion typically remains less than 0.1%. The typical 3 dB bandwidth for small signal inputs is 800 kHz. 12 9 11 1 GND *ADDITIONAL PINS OMITTED FOR CLARITY. VSS VDD VOUT VOUT1 R1 10kΩ ±0.1% R2 10kΩ ±0.1% +15V –15V VREF AD7228* VREF 10 DAC 1 Figure 11. Bipolar Output Circuit +10V REFERENCE INPUT 15kΩ +15V –5V 10kΩ +2V 12 9 11 1 GND *ADDITIONAL PINS OMITTED FOR CLARITY. VSS VDD VOUT1 VREF +15V AD7228* 10 DAC 1 +4V –4V Figure 12. Applying an AC Signal to the AD7228 |
同様の部品番号 - AD7228KN |
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同様の説明 - AD7228KN |
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