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(多图) 用没有直流偏压端口的分析器执行PSRR测试

作者:END/David Karpaty?? Analog Devices?? Wilmington?? MA; Edited by Charles H Small and Fran Granville?? 2007年08月03日 ?? 收藏0

  Building the buffer/inverting summer with an AD8034 dual amplifier is a good choice because it has a supply range of 5 to 24V; a signal-frequency response well beyond 1 MHz; and a large capacitive-load-drive capability, allowing you to neglect the capacitance of test cables. Further, the AD8034 can deliver as much as 40 mA of load current.

  To instill confidence that this buffer/inverting-summer configuration works, Figure 2 proves that you can neglect any loss that the AD8034 incurs. The figure demonstrates that the response of the AD8034 buffer/inverting summer of 10 Hz to 10 kHz is approximately flat with a loss of only 0.0025 dB, and the loss from 10 to 100 kHz is approximately 0.024 dB. Figure 3 shows negative-PSRR test results. The Hewlett-Packard HP8753 provides the PSRR-versus-frequency responses beyond 100 kHz. You can measure positive PSRR (figure 4 and figure 5) by connecting Pin 3 to the SR785’s output port. Pin 1, VOUT of the buffer amplifier, connects to the reference port of the SR785. Here, you use the first amp to isolate the output port of the SR785 from the dc bias and provide the sinusoidal output. The second amplifier within the AD8034 sums the dc bias and sinusoid, which you use to feed the DUT’s positive-supply pin. You must remove all bypass capacitors at the DUT’s positive-supply pin. A 1-kΩ resistor from Pin 3 to ground prevents the noninverting input from floating. Feed the negative terminal of the external dc-power supply to Pin 6 through a 1-kΩ resistor. Connecting the DUT’s output to Channel 2A of the SR785 completes the test-circuit configuration.

  For the AD8034, assume that the DUT has a maximum supply voltage of ±15V, that you need to test negative PSRR, and that the DUT supplies ±10V. If you want to accommodate the maximum SR785 output of 5V peak, the first amplifier of the AD8034 needs enough head room to avoid clipping the ±5V signal from the output port of the SR785. In this case, a supply setting for the AD8034 of 6 and –16V is sufficient to prevent any problems. This amount provides enough head room to accommodate the first amp of the AD8034, which handles a ±5V signal centered at ground. The –16V accommodates the dc bias of –10V and the ±5V signal centered at –10V at the output of the second amplifier of the AD8034. Positive PSRR is similar: Just set the AD8034 supplies to 16 and –6V for this example.

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AD8034? 缓冲逆变累加器?


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