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AD7937AR データシート(PDF) 6 Page - Analog Devices |
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AD7937AR データシート(HTML) 6 Page - Analog Devices |
6 / 8 page AD7937 –6– REV. 0 SEPARATE AGND PINS The DACs in the AD7937 have separate AGND lines taken to pins AGNDA and AGNDB on the package. This increases the applications versatility of the part. Figure 6 is an example of this. DAC A is connected in standard fashion as a programmable attenuator. AGNDA is at ground potential. DAC B is operating with AGND B biased to 5 V by the AD584. This gives an out- put range of 5 V to 10 V. IOUTA AGNDA RFBA A1 VREFA IOUTB AGNDB RFBB VDD DGND DATA INPUT AD7937* DB7 DB0 *CONTROL CIRCUITRY OMITTED FOR CLARITY DAC A 20V p–p A2 DAC B VREFB AD584 5V SIGNAL GROUND VOUTB = 5V TO 10V VOUTA VDD = 5V Figure 6. DACs Used in Different Modes PROGRAMMABLE OSCILLATOR Figure 7 shows a conventional state variable oscillator in which the AD7937 controls the programmable integrators. The frequency of oscillation is given by: f = 1 2 π R6 R5 × 1 C1 ×C2× REQ1× REQ2 where REQ1 and REQ2 are the equivalent resistances of the DACs. The same digital code is loaded into both DACs. If C1 = C2 and R5 = R6, the expression reduces to f = 1 2 π × 1 C 1 REQ1 × R EQ2 Since REQ = 2n × R LAD N , (RLAD = DAC ladder resistance). f = 1 2 π × 1 C (N /2n )2 RLAD1 × R LAD2 = 1 2 π × D C 1 RLAD1 × R LAD2 D = N 2n = 1 2 π × D C × R LAD m where m is the DAC ladder resistance mismatch ratio, typically 1.005. With the values shown in Figure 7, the output frequency varies from 0 Hz to 1.38 kHz. The amplitude of the output signal at the A3 output is 10 V peak-to-peak and is constant over the entire frequency span. IOUTA AGNDA 1/2 AD7937 R6 10k VOUT R4 200k A1 1/2 AD712 10k A2 DAC A VREFA C1 10,000pF IOUTB AGNDB 1/2 AD7937 1/2 AD712 A3 DAC B VREFB C2 10,000pF R5 10k AD711 FREQUENCY SELECT CODE 5.1V NOTE DAC CONTROL INPUTS OMITTED FOR CLARITY Figure 7. Programmable State Variable Oscillator |
同様の部品番号 - AD7937AR |
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同様の説明 - AD7937AR |
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