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AD7568BSZ Datasheet(PDF) 8 Page - Analog Devices |
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AD7568BSZ Datasheet(HTML) 8 Page - Analog Devices |
8 / 14 page AD7568 –8– UNIPOLAR BINARY OPERATION (2-Quadrant Multiplication) Figure 15 shows the standard unipolar binary connection dia- gram for one of the DACs in the AD7568. When VIN is an ac signal, the circuit performs 2-quadrant multiplication. Resistors R1 and R2 allow the user to adjust the DAC gain error. Offset can be removed by adjusting the output amplifier offset voltage. A1 should be chosen to suit the application. For example, the AD OP07 or OP177 are ideal for very low bandwidth applica- tions while the AD843 and AD845 offer very fast settling time in wide bandwidth applications. Appropriate multiple versions of these amplifiers can be used with the AD7568 to reduce board space requirements. The code table for Figure 15 is shown in Table III. DAC A A1 I A OUT1 I A OUT2 AD7568 V OUT R A FB V A REF V IN NOTES 1. ONLY ONE DAC IS SHOWN FOR CLARITY. 2. DIGITAL INPUT CONNECTIONS ARE OMITTED. 3. C1 PHASE COMPENSATION (5–15pF) MAY BE REQUIRED WHEN USING HIGH SPEED AMPLIFIER, A1. R2 10 Ω R1 20 Ω SIGNAL GND A1: OP-177 ADOP-07 AD711 AD843 AD845 C1 Figure 15. Unipolar Binary Operation Table III. Unipolar Binary Code Table Digital Input Analog Output MSB………LSB (VOUT As Shown in Figure 15) 1111 1111 1111 –VREF (4095/4096) 1000 0000 0001 –VREF (2049/4096) 1000 0000 0000 –VREF (2048/4096) 0111 1111 1111 –VREF (2047/4096) 0000 0000 0001 –VREF (1/4096) 0000 0000 0000 –VREF (0/4096) = 0 NOTE Nominal LSB size for the circuit of Figure 15 is given by: VREF (1/4096). BIPOLAR OPERATION (4-Quadrant Multiplication) Figure 16 shows the standard connection diagram for bipolar operation of any one of the DACs in the AD7568. The coding is offset binary as shown in Table IV. When VIN is an ac signal, the circuit performs 4-quadrant multiplication. To maintain the gain error specifications, resistors R3, R4 and R5 should be ra- tio matched to 0.01%. DAC A A1 I A OUT1 I A OUT2 AD7568 V OUT R A FB V A REF V IN NOTES 1. ONLY ONE DAC IS SHOWN FOR CLARITY. 2. DIGITAL INPUT CONNECTIONS ARE OMITTED. 3. C1 PHASE COMPENSATION (5–15pF) MAY BE REQUIRED WHEN USING HIGH SPEED AMPLIFIER, A1. R2 10 Ω R1 20 Ω SIGNAL GND C1 A2 R3 10k Ω R5 20k Ω 20k Ω R4 Figure 16. Bipolar Operation (4-Quadrant Multiplication) Table IV. Bipolar (Offset Binary) Code Table Digital Input Analog Output MSB . . . . . LSB (VOUT As Shown in Figure 16) 1111 1111 1111 +VREF (2047/2048) 1000 0000 0001 +VREF (1/2048) 1000 0000 0000 +VREF (0/2048) = 0 0111 1111 1111 –VREF (1/2048) 0000 0000 0001 –VREF (2047/2048) 0000 0000 0000 –VREF (2048/2048) = –VREF NOTE Nominal LSB size for the circuit of Figure 16 is given by: VREF (1/2048). SINGLE SUPPLY CIRCUITS The AD7568 operates from a single +5 V supply, and this makes it ideal for single supply systems. When operating in such a system, it is not possible to use the standard circuits of Figures 15 and 16 since these invert the analog input, VIN. There are two alternatives. One of these continues to operate the DAC as a current-mode device, while the other uses the voltage switch- ing mode. DAC A A1 I A OUT1 I A OUT2 AD7568 V BIAS V OUT R A FB V A REF V IN NOTES 1. ONLY ONE DAC IS SHOWN FOR CLARITY. 2. DIGITAL INPUT CONNECTIONS ARE OMITTED. 3. C1 PHASE COMPENSATION (5–15pF) MAY BE REQUIRED WHEN USING HIGH SPEED AMPLIFIER, A1. Figure 17. Single Supply Current-Mode Operation REV. C |
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