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AD5263BRUZ200-R7 数据表(PDF) 24 Page - Analog Devices |
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AD5263BRUZ200-R7 数据表(HTML) 24 Page - Analog Devices |
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24 / 28 page ![]() AD5263 Data Sheet Rev. F | Page 24 of 28 8-BIT BIPOLAR DAC Figure 60 shows a low cost, 8-bit, bipolar DAC. It offers the same number of adjustable steps, but not the precision as compared to conventional DACs. The linearity and temperature coefficient, especially at low values codes, are skewed by the effects of the digital potentiometer wiper resistance. The output of this circuit is REF O V D V × − = 1 256 2 (4) A B A1 W U1 VIN GND VO 1 VOUT ADR425 +15V TRIM +5VREF –5VREF A2 VI AD5263 OP2177 V– V+ +15V –15V OP2177 V– V+ Figure 60. 8-Bit Bipolar DAC BIPOLAR PROGRAMMABLE GAIN AMPLIFIER For applications requiring bipolar gain, Figure 61 shows one implementation similar to the previous circuit. The digital potentiometer U1 sets the adjustment range. The wiper voltage at W2 can therefore be programmed between VI and –KVI at a given U2 setting. Configuring A2 in the noninverting mode allows linear gain and attenuation. The transfer function is ( ) − + × × + = K K D2 R1 R2 V V I O 1 256 1 (5) where K is the ratio of RWB1/RWA1 set by U1. A1 AD5263 W1 VO A2 A2 B2 VSS VDD U2 –KVI B1 A1 C1 VI R2 R1 AD5263 U1 W2 VDD VSS OP2177 V– V+ OP2177 V– V+ Figure 61. Bipolar Programmable Gain Amplifier Similar to the previous example, in the simpler (and much more usual) case where K = 1, a single channel is used and U1 is replaced by a matched pair of resistors to apply VI and –VI at the ends of the digital potentiometer. The relationship becomes I O V D2 R1 R2 V × − × × + = 1 256 2 1 (6) If R2 is large, a compensation capacitor of a few pF may be needed to avoid any gain peaking. Table 10 shows the result of adjusting D, with A2 configured with unity gain, gain of 2, and gain of 10. The result is a bipolar amplifier with linearly programmable gain and 256-step resolution. Table 10. Result of Bipolar Gain Amplifier D R1 = ∞, R2 = 0 R1 = R2 R2 = 9 × R1 0 –1 –2 –10 64 –0.5 –1 –5 128 0 0 0 192 0.5 1 5 255 0.968 1.937 9.680 PROGRAMMABLE VOLTAGE SOURCE WITH BOOSTED OUTPUT For applications that require high current adjustment, such as a laser diode driver or tunable laser, a boosted voltage source can be considered. See Figure 62. +V W SIGNAL CC RBIAS LD VIN A B VOUT U1 AD5263 U3 2N7002 U2 –V IL AD8601 Figure 62. Programmable Booster Voltage Source In this circuit, the inverting input of the op amp forces the VOUT to be equal to the wiper voltage set by the digital potentiometer. The load current is then delivered by the supply via the N-channel FET, N1. N1 power handling must be adequate to dissipate power equal to (VIN − VOUT) × IL. This circuit can source a maximum of 100 mA with a 5 V supply. For precision applications, a voltage reference such as ADR421 or ADR03 can be applied at the A terminal of the digital potentiometer. |
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